- Water Gateshead & Newcastle Councils December 2011
NewcastleGateshead Surface Water Management Plan
Identifying Areas at Risk Final Report Prepared by: Christian Lomax Checked by: Daniel Alstead Principal Consultant Consultant
Approved by: Roy Lobley Associate Director
Rev No Comments Checked by Approved Date by 0 Draft Report DJA VH Aug 2011 1 Draft Final Report DJA RL Sept 2011 2 Final Report DJA RL Dec 2011
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Job No 60198244 Reference SWMP Stage 3 Date Created December 2011
This document has been prepared by AECOM Limited for the sole use of our client (the “Client”) and in accordance with generally accepted consultancy principles, the budget for fees and the terms of reference agreed between AECOM Limited and the Client. Any information provided by third parties and referred to herein has not been checked or verified by AECOM Limited, unless otherwise expressly stated in the document. No third party may rely upon this document without the prior and express written agreement of AECOM Limited. Table of Contents
Abbreviations ...... i
Glossary ...... ii
1 Introduction...... 5 1.1 What is a Surface Water Management Plan? ...... 5 1.2 SWMP Partnership ...... 5 1.3 Scope of the NewcastleGateshead SWMP ...... 8
2 SWMP Analysis ...... 11 2.1 Phase 1: Preparation ...... 11 2.2 Phase 2: Risk Assessment ...... 11 2.3 Phase 3: Options ...... 22 2.4 Phase 4: Implementation and Review ...... 26
3 Key Findings & Action Plan ...... 29 3.1 Surface Water Flood Risk ...... 29 3.2 Managing Surface Water ...... 30 3.3 Action Plan ...... 32 3.4 Going Forward ...... 33
4 Funding for Surface Water Management ...... 38 4.1 Introduction ...... 38 4.2 Local Authorities ...... 38 4.3 Business ...... 39 4.4 Community Self Help ...... 39 4.5 Resistance and Resilience Measures...... 41
5 Summary ...... 44 5.1 Surface Water Principles ...... 44 5.2 Actions ...... 45
List of Appendices
Appendix A – Gateshead Hotspots Priority Matrix ...... 46 Appendix B– Newcastle Hotspots Priority Matrix ...... 48 Appendix C – Gateshead Hotspot Data Sheets ...... 50 Appendix D– Newcastle Hotspot Data Sheets ...... 107
List of Tables
Table 1.1: Roles & Responsibilities ...... 7 Table 2.1: Weighting Applied to Prioritise Hotspots ...... 20 Table 2.2: Top Ten Hotspots for Gateshead ...... 21 Table 2.3: Top Ten Hotspots for Newcastle...... 22 Table 2.4: 18 Hotspots Identified by the Partners ...... 23 Table 3.1: Development sites that provide opportunities to manage the risk of surface water flooding ...... 31 Table 3. 2: Action Plan Categories ...... 32 Table 3.3: Flood Incident Register used by the Councils ...... 33 Table 3.4: Action Plan for the Gateshead and Newcastle ...... 34 List of Figures
Figure 2.1: Records of Surface Water Flooding in Gateshead ...... 13 Figure 2.2: Records of Surface Water Flooding in Newcastle ...... 13 Figure 2.3: Gateshead Surface Water Hotspots ...... 15 Figure 2.4: Newcastle Surface Water Hotspots ...... 16 Figure 2.5: Topographic Catchments ...... 17 Figure 2.6: Sewer Drainage Areas ...... 18 Figure 2.7: Iterative Nature of SWMPs ...... 27
List of Photographs
Photograph 1: Flooding on Eldon Square in 2010 ...... 126 Photograph 2: Flooding on Northumberland Street in 1913 ...... 126 Photograph 3: Historic Flooding along Newgate Street in 2010 ...... 134 Photograph 4: Historic Flooding along Newgate Street in 2010 ...... 134 Photograph 5: Historic Flooding along Quayside in 2010 ...... 134 Photograph 6: Historic Flooding along Quayside in 2010 ...... 134 Photograph 7: Historic Flooding along Diana Street in 2010 ...... 134 Photograph 8: Historic Flooding along Chatsworth Gardens in 1941 ...... 159 Photograph 9: Historic Flooding along Buxton Gardens in 1941 ...... 159 AECOM Surface Water Management Plan i
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Abbreviations
AEP Annual Exceedance Probability
AMP Asset Management Plan
DA Drainage Area
Defra Department Environment, Food and Rural Affairs
ELR Employment Land Review
GH Gateshead Hotspot
GI Green Infrastructure
GIS Geographical Information System
LDF Local Development Framework
MCA Multi Criteria Analysis
NH Newcastle Hotspot
PFRA Preliminary Flood Risk Assessments
SFRA Strategic Flood Risk Assessment
SHLAA Strategic Housing Land Availability Assessment
SLR Strategic Land Review
STW Sewage Treatment Works
SuDS Sustainable Drainage Systems
SWMP Surface Water Management Plan
WCS Water Cycle Study
WFD Water Framework Directive AECOM Surface Water Management Plan ii
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Glossary
Annual Exceedance Probability (AEP) - The probability (%) that a given rainfall total accumulated over a given duration will be exceeded in any one year. I.e. the ‘1 in 100 year event’ has a 1% probability of occurring each year. Areas Susceptible to Surface Water Flooding – National mapping prepared by the Environment Agency in 2008 illustrating the flooding that takes place from the 'surface runoff' generated by rainwater (including snow and other precipitation) which: (a) is on the surface of the ground (whether or not it is moving), and (b) has not yet entered a watercourse, drainage system or public sewer. Average recurrence interval (ARI) ‘1 in 100 year event’- The average or expected value of the periods between exceedances of a given rainfall total accumulated over a given duration. It is implicit in this definition that the periods between exceedances are generally random. Boundary Flow Interception – Capturing or addressing surface water flows before they reach the boundary of a hotspot. Core Strategy – A Development Plan Document setting out the spatial vision and strategic objectives of the planning framework for Gateshead and Newcastle. Department for Environment, Food and Rural Affairs (Defra) – Department that brings together the interests of farmers and the countryside; the environment and the rural economy; the food we eat, the air we breathe and the water we drink. Development Plan Document (DPD) – Local Development Framework document that contain policies and are subject to external examination by an independent Inspector. Employment Land Review (ELR) - provides an evidence base that will be used to inform the preparation of employment land policies and allocations in the Local Development Framework (LDF). The ELR ensures that sites and buildings that are important to the future prosperity of an area are retained in employment use and to enable the release of sites that could sensibly be used for other purposes. Environment Agency (EA) – The Environment Agency was established under the Environment Act 1995, and is a Non- Departmental Public Body of Defra. The Environment Agency is the leading public body for protecting and improving the environment in England and Wales today and for future generations. The organisation is responsible for wide ranging matters, including the management of all forms of flood risk, water resources, water quality, waste regulation, pollution control, inland fisheries, recreation, conservation and navigation of inland waterways. It will also have a new strategic overview for all forms of inland flooding Flood Map for Surface Water – National mapping prepared by the Environment Agency in 2009 to improve the Areas Susceptible to Surface Water Flooding using improved model data. Flood Risk Assessment (FRA) – a FRA is required under PPS25 at the planning application stage for new developments. An FRA will demonstrate how flood risk from all sources to the development itself and flood risk to others will be managed now and in the future (including climate change). Floods and Water Management Act (2010) – Act of Parliament to clarify the legislative framework for managing surface water flood risk in England. Green Infrastructure –is the network of multifunctional green and undeveloped land, urban and rural, which supports the activity, health and well being of local people and wildlife. Growth Point – communities that are pursuing large-scale, sustainable housing growth through a partnership between local organisations and central government. AECOM Surface Water Management Plan iii
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Local Authority or Local Planning Authority (LA or LPA) – the Local Authority or Council that is empowered by law to exercise planning functions. Often the Local Borough or District Council, National Parks and the Broads Authority are also considered to be local planning authorities. County Councils are the authority for waste and minerals matters. Local Development Framework (LDF) – a folder of local development documents that outlines how planning will be managed in the area. Main River – Generally main rivers are larger streams or rivers, but can be smaller watercourses. Main Rivers are determined by Defra in England, and the Environment Agency has legal responsibility for them. Ofwat – The Water Services Regulation Authority (Ofwat) is the body responsible for economic regulation of the privatised water and sewerage industry in England and Wales. Ofwat is primarily responsible for setting limits on the prices charged for water and sewerage services, taking into account proposed capital investment schemes (such as building new wastewater treatment works) and expected operational efficiency gains. Ordinary watercourse - An ordinary watercourse is any other river, stream, ditch, cut, sluice, dyke or non-public sewer which is not a Main River. The Local Authority has powers for such watercourses. Pitt Review - An independent review of the 2007 summer floods by Sir Michael Pitt, which provided recommendations to improve flood risk management in England. Planning Policy Statements (PPS) and Planning Policy Guidance (PPG) – these documents set out the Government’s national policies on different aspect of planning. The policies in these statements apply throughout England and focus on procedural policy and the process of preparing local development documents. Strategic Flood Risk Assessment (SFRA) – an assessment of flood risk from all sources which is used to inform the planning process of flood risk and provides information on future risk over a wide spatial area. It is also used as a planning tool to examine the sustainability of the proposed development allocations. SFRAs form the basis of flood risk management in England and are a requirement of PPS25. Supplementary Planning Documents (SPD) - supplementary planning documents can give further context and detail to local development plan policies. It is not part of the statutory development plan. Therefore, it does not have the same weight when local planning authorities are considering planning applications. Surface Water Flooding - surface water flooding describes flooding from sewers, drains, groundwater, and runoff from land, small water courses and ditches that occurs as a result of heavy rainfall. Surface Water Management Plan (SWMP) - is a plan which outlines the preferred surface water management strategy in a given location. Sustainable Drainage Systems (SuDS) – Sustainable drainage systems (previously referred to as sustainable urban drainage systems): a sequence of source control, management practices and control structures designed to drain surface water in a more sustainable fashion than some conventional techniques (may also be referred to as SuDS or SDS). Water Cycle Study (WCS) – The purpose of a WCS is to strategically plan the most sustainable water infrastructure in a timely manner, across all of the water cycle from water supply and water resources, flood risk and surface water drainage, and wastewater and biodiversity. Water Framework Directive (WFD) – A European Community Directive (2000/60/EC) of the European Parliament and Council designed to integrate the way water bodies are managed across Europe. It requires all inland and coastal waters to reach “good status” by 2015 through a catchment-based system of River Basin Management Plans, incorporating a programme of measures to improve the status of all natural water bodies. Introduction AECOM Surface Water Management Plan 5
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1 Introduction
1.1 What is a Surface Water Management Plan? The Surface Water Management Plan (SWMP) Technical Guidance1 states that a SWMP is:
“a plan which outlines the preferred surface water management strategy in a given location. In this context surface water flooding describes flooding from sewers, drains, groundwater, and runoff from land, small watercourses and ditches that occurs as a result of heavy rainfall.”
In addition the guidance stresses the need for local partners with responsibility for surface water and drainage to work together to understand the causes of surface water flooding and agree the most cost effective way of managing the risk of surface water flooding. It further states the need to make surface water management decisions that are evidence based, risk based, future proofed and are inclusive of stakeholder views and preferences. The SWMP can be used to inform Preliminary Flood Risk Assessments (PFRAs) under the Flood and Water Management Act (2010) and fulfil the requirement for Flood Risk Management Plans under the Flood Risk Regulations (2009). Surface water flooding occurs when severe rainfall events generate runoff which exceeds the capacity of surface water conveyance systems including natural watercourses and man-made drainage systems. Surface water flooding may develop quickly, especially in urban areas and is often difficult to predict. Current predictions of the impacts of climate change suggest more frequent short-duration, high intensity rainfall and more frequent periods of long-duration rainfall. This reinforces the need to manage surface water for the present and future situation. From a planning perspective SWMPs can provide a framework to deal with surface water flooding for new developments, whilst contributing to improving the water quality of our water networks and achieving the requirements of the Water Framework Directive (WFD). There are four phases to a SWMP:
- Phase 1 – Preparation: identifies Partners and Stakeholders who need to be involved in the study and clarifies their roles and responsibilities.
- Phase 2 – Risk Assessment: reviews the risk of surface water flooding.
- Phase 3 – Options: identifies measures by which the surface water flood risks can be mitigated. The mitigation measures, or options, are prioritised and analysed in terms of their suitability and practicality.
- Phase 4 – Implementation & Review: the preferred options are implemented by the Partners. A review of the SWMP should be periodically carried out to identify areas that have benefited from the study and recommend any areas of improvement or identify gaps in the study. 1.2 SWMP Partnership The nature of SWMPs varies from location to location depending on local variables and the type of problem encountered. As a result the organisations who need to be involved with a SWMP will also vary. Four Key Partners have been identified for the NewcastleGateshead SWMP; two Local Authorities (Gateshead Council & Newcastle City Council, referred to as ‘the Councils’), Northumbrian Water and the Environment Agency. Each of the four Partners has an important role to play concerning flood risk. The following sections outline their roles and responsibilities and summarises how the outputs of the SWMP will be of use to each organisation.
1 Defra (March 2010). Surface Water Management Plan Technical Guidance. AECOM Surface Water Management Plan 6
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1.2.1 Gateshead Council & Newcastle City Council
The Councils are responsible for planning and managing development within their local authority area, with due regard to the risk of flooding and have a number of permissive powers under the Land Drainage Act and Public Health Act to undertake drainage works in relation to watercourses. The Councils, in their capacity as a highways authority also have powers with regard to the drainage of highways. Under the Flood and Water Management Act, the Councils have been given the lead in managing a local flood risk management strategy and will become the approving and adopting body for all Sustainable Drainage Systems (SuDS). All drainage systems in new developments and redevelopments that include SuDS schemes will need to be approved by the Councils before construction can commence. Should the SuDS scheme serve more than one property, the Councils would subsequently adopt and maintain the scheme where constructed as approved. It will be important for schemes to be accompanied by maintenance plans to ensure that the effectiveness of schemes does not decrease over time. The Councils are the Lead Partners and have responsibility for the SWMP. Outputs from the SWMP will be used by the Councils to carry out other activities such as emergency planning, control drainage, review Local development Framework (LDF) land allocations, and develop investment programmes, at the same time as satisfying the requirements of the Flood and Water Management Act and contributing to the evidence base supporting the Core Strategy. 1.2.2 Environment Agency
The Environment Agency is an Executive Non-departmental Public Body responsible to the Secretary of State for Environment, Food and Rural Affairs (England) and an Assembly Sponsored Public Body responsible to the National Assembly for Wales. The organisation’s aims are to protect and improve the environment, and to promote sustainable development. The Environment Agency plays a central role in delivering the environmental priorities of central government and the Welsh Assembly Government through their functions and roles. The Environment Agency has a general supervisory duty relating to all flood defence related matters under the Environment Act and the Flood and Water Management Act has given the Environment Agency an overview of all flood and coastal erosion risk management. The extent of the Environment Agency’s operational role greatly depends upon the designation of a watercourse as Main River. The power of the Environment Agency to maintain and improve existing works and construct new works is a permissive one. The Environment Agency is an essential Partner in the SWMP. The outputs from the SWMP will be issued to the Environment Agency to review and assess existing and new emergency plans, communicate with local residents on flood risk issues, and finalise asset management plans (investment, operations and maintenance). 1.2.3 Northumbrian Water
Northumbrian Water is the supplier of water and sewerage services for Gateshead and Newcastle comprising water resources distribution and collection, surface water drainage, wastewater collection and disposal. The water company has the responsibility (amongst others) for ensuring that its drainage network is maintained and improved to cope with surface water flooding. This is not an absolute responsibility, as sewerage undertaker’s funds are not unlimited and investment in sewers must be prioritised. There is broad agreement that this responsibility is limited to flooding arising from the 3.33% Annual Exceedance Probability (AEP) (1 in 30 year return period) event for new developments whereas it is the 5% AEP (1 in 20 year) for existing networks. Northumbrian Water will identify strategies in order to address issues and apply for funding from OFWAT to deliver the schemes. Asset management and investment in water companies occurs in Asset Management Plan (AMP) periods. Each period has an investment programme to improve and maintain current assets and invest in new development areas. Northumbrian Water has AECOM Surface Water Management Plan 7
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recently commenced their next investment period, AMP5: 2010-2015, therefore the outputs from the SWMP will only be able to influence their priorities to a limited extent. However as the company makes progress during the AMP5 period, their asset improvement plan could be reviewed to include the recommendations of the SWMP. It is however more likely that the SWMP will inform work in AMP6. Northumbrian Water is an essential partner in the SWMP. The outputs from the SWMP will be used by Northumbrian Water to undertake their Drainage Area and Sewerage Management Plans, plan their investment and respond to development pressures. Table 1.1 sets out what each Partner is required to contribute to the SWMP and the benefits that will arise. Table 1.1: Roles & Responsibilities Partner Role How they inform the What they get out of the SWMP SWMP
The SWMP acts as a vital evidence base to the Core Strategy, showing surface water flooding has been considered during the strategic planning process. The study provides information and assurances that the Councils growth and regeneration aspirations can be supplied with due Lead partner responsible Provision of information regard for flood risk. for future development, concerning future Local surface water, local flood development; locations, The SWMP will ensure a joined up approach Authority risk management and that phasing and numbers and between land owners, water infrastructure a partnership approach is surface water drainage providers and planners during strategic growth and adopted. data. regeneration planning. The SWMP will help to ensure that the natural water environment is protected and work with the Green Infrastructure Strategy to support the activity, health and well being of local people and wildlife through the provision of green space.
An appreciation and understanding of the local Essential partner authorities growth aspirations, when development responsible for ensuring will come forward, where and the phasing. that its drainage network is Contribute to the The SWMP can inform long term planning, Northumbrian maintained and improved identification and identifying where and when investment is required. Water to cope with surface water assessment of areas at risk flooding for flows up to the of surface water flooding. An opportunity to comment on the proposed 5% AEP (1 in 20 year growth to influence the location and timing of future return period) event. development by supporting proposals or make recommendations for changes.
Encourage sustainable development. Essential partner Provision of information Participate in and prove partnership working. Environment responsible for flood risk, and data concerning the Agency development control and water environment and its Achieve efficiencies of working, support growth water quality. constraints and limitations. and ensure it is sustainable with regard to the environment. AECOM Surface Water Management Plan 8
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1.3 Scope of the NewcastleGateshead SWMP The average annual rainfall for Gateshead and Newcastle is approximately 665mm, which is lower than the average rainfall for the rest of England however; the varied topography of the area along the River Tyne and its tributaries has a major influence on surface water runoff and flow patterns. The impact of development over time has exerted an impact on the runoff patterns, rates and volumes, consequently stressing the drainage infrastructure and its ability to cope with future expansion. Additionally there have been reported cases of surface water flooding across the study area, which further reinforces the need for a SWMP which will provide a holistic approach to addressing the risk of surface water flooding. The primary purpose of the SWMP is to contribute robust evidence to support the Core Strategy and other LDF documents being developed by the Councils. However it is much more than simply a planning document given its capacity to provide all four Partners with information concerning surface water risks across Gateshead and Newcastle, and in recommending solutions to manage the risks. The SWMP is a high level, strategic document which serves as a starting point for the Partners to address surface water flood risk. It should be noted that the SWMP ought to remain a living document, to be up dated as further data and information becomes available. One of the actions to come out of the SWMP is for the Councils to take the lead in continuing the Partnership working to manage surface water across Gateshead and Newcastle. The NewcastleGateshead SWMP comprises five documents; 1. Scoping Report – documents Phase 1 of the SWMP process for the Strategic Development Sites. 2. Strategic Development Sites – documents Phases 2 to 4 for thirteen development sites that the Councils considered to be important to the Core Strategy. 3. Identifying Areas at Risk – documents Phases 2 to 4 for all of Gateshead and Newcastle. 4. Surface Water Management Strategy – provides a summary of the surface water issue facing Gateshead and Newcastle and the measures by which it is being addressed to ensure sustainable development. 5. Engagement Plan – documents the engagement process that was undertaken as part of the SWMP. This report has identified areas at risk of surface water flooding across Gateshead and Newcastle and through the SMWP process has used a number of risk areas to draw out key surface water principles and develop an Action Plan to ensure that surface water is managed sustainably over the coming years. It should be noted that the SWMP is the starting point in addressing the issues pertaining to surface water flood risk and its completion does not undermine the need to review or address future surface water issues.
1.4 Links with Other Studies In addition to the SWMP, the Councils are producing a number of documents as part of their LDF to ensure a sustainable future for Gateshead and Newcastle. Two of these are directly relevant, and integral to the SWMP; the Strategic Flood Risk Assessment (SFRA) and Water Cycle Study (WCS). Separate SFRAs have been completed for Gateshead and Newcastle which outlined Critical Drainage Areas. The SFRAs informed the SWMP and were integrated with other data-sets as part of the Risk Assessment phases of the SWMP. The WCS reviewed the ability of the water environment (including existing infrastructure) to support future development across Gateshead and Newcastle. Large parts of Gateshead and Newcastle are served by combined sewers which carry wastewater AECOM Surface Water Management Plan 9
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from households and industry, and surface water runoff. These combined sewer systems tend to be located in the older, historic parts of the study area, whereas more recent development has implemented separate sewer systems. The combined sewers and the associated Sewage Treatment Works (STW) have been identified as a potential constraint to future development. Northumbrian Water have identified the removal of surface water from these combined sewers as their preferred means of freeing up capacity within the sewers and at the STW to support future growth. It is likely that a combination of retro-fitting existing developments served by combined sewers to separate the waste- and surface water, and the re- development of brownfield land offers the means of providing this capacity. This issue is given further consideration within the Surface Water Management Strategy. Another document relevant to the SWMP is the Green Infrastructure (GI) Strategy which will include a network of multifunctional green space and other relevant land and watercourses, which support the activity, health and well being of local people and wildlife. Future development and growth across Gateshead and Newcastle has the potential to play a role in the expansion and reinforcement of the GI networks. The most obvious means of contributing to GI is through the provision of green spaces on development sites and through SuDS which can create water features, although the identification of deficiencies in existing water infrastructure that require intervention may also present opportunities to contribute towards GI. The Councils have also produced PFRAs which were informed by interim deliverables produced by the SWMP and are key documents informing the preparation of future Local Flood Risk Management Strategies as required by the Flood and Water Management Act. The PFRAs have located areas in which the risk of surface water and groundwater flooding is significant and warrants further examination through the production of maps and management plans. 1.4.1 MetroGreen Flood Management Plan
A flood management plan has been prepared for MetroGreen; a key development site in Gateshead. The plan considers viable flood mitigation options to bring forward significant housing development around the MetroCentre. There are a number of large sites in and around the MetroCentre, where the Gateshead Sustainable Community Strategy recognises the potential for mixed- use development. Gateshead’s Strategic Housing Land Availability Assessment (SHLAA) and Employment Land Review (ELR) recognise the area as a medium to long term aspiration. Both reports recommend widening the range of uses in the area to permit a mix of uses including residential. The MetroGreen area comprises eight distinct land parcels containing 27 individual sites. The MetroGreen flood management plan provides the level of information needed to support the Core Strategy and Area Action Plan and site specific Development Plan Documents. Its main objective was to identify a number of development options, which fit with both the development aspirations of MetroGreen whilst tackling the key constraints in a sustainable manner. This informs Gateshead Council about type, form and location of development in this area, complying with PPS25. SWMP Analysis AECOM Surface Water Management Plan 11
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2 SWMP Analysis
This chapter provides a concise summary of the work that was undertaken to identify areas at risk of surface water flooding across Gateshead and Newcastle. 2.1 Phase 1: Preparation For the Preparation phase the SWMP Partnership was established. Due to the nature of the study the Partners were restricted to the Councils, the Environment Agency and Northumbrian Water. The Partners are outlined in Section 1.2 of this report. 2.2 Phase 2: Risk Assessment The principal purpose of the Risk Assessment was to strategically identify areas considered to be at risk of surface water flooding across Gateshead and Newcastle. As the assessment operates at a broad and strategic level, the SWMP guidance recommends that the analysis should be based on existing information or the use of simple analysis methods to improve existing information and make maximum use of existing data and information. Given the geographical scale of the assessment, the Risk Assessment should be used to flag locations requiring a more detailed appraisal and to help prioritise further studies. 2.2.1 Review Data and Identify Hotspots The first step in the analysis was to identify areas across Gateshead and Newcastle considered to be at risk of surface water flooding. Areas considered to be at risk, termed “hotspots,” were delineated based on the following datasets:
- Flood Map for Surface Water,
- Areas Susceptible to Surface Water Flooding,
- Known Flood Incidents, and
- SFRAs and associated data.
The Flood Map for Surface Water shows areas where surface water would be expected to flow or pond and comprises four flood extents: 1. Flooding from a 3.33% AEP event (1 in 30 year rainfall event) greater than 0.1m deep, 2. Flooding from a 3.33% AEP event greater than 0.3m deep, 3. Flooding from a 0.5% AEP event (1 in 200 year rainfall event) greater than 0.1m deep, and 4. Flooding from a 0.5% AEP event greater than 0.3m deep. The Flood Map for Surface Water is an update to the Areas Susceptible to Surface Water Flooding, however the Environment Agency advised that due to limitations with both datasets, both should be used to inform the project. The Areas Susceptible to Surface Water Flooding may be preferable in flat and rural areas. The Areas Susceptible to Surface Water Flooding data is the representation of the 0.5% AEP event and is sub-divided into three categories; ‘More’, ‘Intermediate’ and ‘Less’ susceptible. The ‘More’ and ‘Intermediate’ Areas Susceptible to Surface Water Flooding were used to identify hotspots in rural and flat areas that might have been missed by the Flood Map for Surface Water. They were also used to ascertain whether there was any correlation with the Flood Map for Surface Water data. Where the correlation was good the hotspot boundaries were refined to reflect any additional flooding from the Areas Susceptible to Surface Water Flooding. The key differences between the datasets are that the Flood Map for Surface Water has included allowances for infiltration to impermeable surfaces and the sewer system and included buildings, whereas the Areas Susceptible to Surface Water Flooding AECOM Surface Water Management Plan 12
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assumed all of the rainfall stayed on the ground surface and had excluded buildings assuming a flat surface for the water to flow over. The other key difference was the storm duration used by each dataset. The Flood Map for Surface Water used a 1.1 hour storm whereas the Areas Susceptible to Surface Water Flooding had the 0.5% AEP event occurring over a six hour period. Known surface water incidents were then assessed to see if there were any clusters of known flooding that were not reflected in the Flood Map for Surface Water or Areas Susceptible to Surface Water Flooding. Where this was the case additional hotspots were created e.g. Bensham. In these instances the hotspot boundary was defined with regard to the sewer drainage area. These hotspots, based purely on known incidents, will require more detailed analysis since the fact that they cluster together does not necessarily mean that they are interrelated. Northumbrian Water provided 100m x 100m grid squares in which sewer flooding has occurred for events up to the 5% AEP (1 in 20 year return period) event; the DG5 register and events greater than the 5% AEP, termed extreme events. The difference between these two data-sets is Northumbrian Water endeavour to resolve DG5 flooding whereas their infrastructure is not designed to cope with extreme flooding therefore they would not normally invest money to address extreme flooding. They also provided Pipe Length References which identify locations where hydraulic incapacities have been identified. The Councils provided data concerning surface water flooding. This information is illustrated in Figures 2.1 and 2.2. The latest draft SFRAs contained additional data concerning known incidents, historic flood outlines, Critical Drainage Areas and watercourse information. This data was used to review if any additional hotspots needed to be defined. The SFRAs note a number of problem areas which do not correlate with the Flood Map for Surface Water or the Areas Susceptible to Surface Water Flooding. However the SFRAs do not always specify site specific areas at risk, instead referring to an area e.g. Birtley therefore, in these instances approximate risk areas have been delineated. Once the data-sets had been reviewed, each hotspot was looked at in more detail to determine whether it should be sub-divided. For example, roads and railways often appear to form a hydraulic break between areas of flooding. The hotspots were subsequently labelled with the prefix ‘GH’ or ‘NH’ for ‘Gateshead Hotspot’ and ‘Newcastle Hotspot’ respectively, followed by a sequential number. 62 hotspots have been delineated for Gateshead and 37 for Newcastle (Figures 2.3 and 2.4 and Appendices A and B). Hotspots have also been delineated beyond the authority boundaries based on the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding. The hotspots have been labelled with a prefix of GHWA and NHWA for Gateshead Hotspot Wider Area and Newcastle Hotspot Wider Area respectively. There are 20 wider area hotspots for Gateshead and 11 wider area hotspots for Newcastle. Once hotspots had been identified, the local drainage areas were reviewed. This is so that the Options phase of the SWMP has an appreciation of the area potentially influencing and being influenced by the hotspots. The key drainage area is the above ground, topographic catchment that influences overland flows. This is particularly relevant given that the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding were based on overland flows. These topographic catchments were provided with the SFRA for Newcastle but had to be defined for Gateshead. This was done using the same method as the Newcastle SFRA, namely the Flood Estimation Handbook CD-ROM. The topographic catchments and hotspots are illustrated in Figure 2.5. However, known flood incidents are often a result of overwhelmed sewer systems, which regularly do not follow the surface topography but cross catchment boundaries. Therefore it is important to have an appreciation of the areas drained by sewer systems. This data-set accompanied each SFRA but does not cover all of the authority areas. Figure 2.6 shows the sewer drainage areas and hotspots for Gateshead and Newcastle. AECOM Surface Water Management Plan 13
Capabilities on project: Water Figure 2.1: Records of Surface Water Flooding in Gateshead
Figure 2.2: Records of Surface Water Flooding in Newcastle AECOM Surface Water Management Plan 14
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Capabilities on project: Water Figure 2.3: Gateshead Surface Water Hotspots AECOM Surface Water Management Plan 16
Capabilities on project: Water Figure 2.4: Newcastle Surface Water Hotspots AECOM Surface Water Management Plan 17
Capabilities on project: Water Figure 2.5: Topographic Catchments AECOM Surface Water Management Plan 18
Capabilities on project: Water Figure 2.6: Sewer Drainage Areas AECOM Surface Water Management Plan 19
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2.2.1.1 Gateshead Hotspots The approach set out above worked well when identifying and delineating hotspots in Gateshead. There is a good correlation between the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding. There are several surface water incidents in and around Bensham however, which have a very poor correlation with the Flood Map for Surface Water or Areas Susceptible to Surface Water Flooding. Given that Bensham is a potential development area further modelling of the sewer systems may prove beneficial. Hotspots have been delineated beyond the Gateshead authority boundary. These do not influence any of the surface water risk areas within Gateshead and have not been considered further but could be of use to the Council in the future for example for comparison purposes with neighbouring authorities. 2.2.1.2 Newcastle Hotspots There is a mixed correlation between the Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding across Newcastle. The correlation is good in the urbanised areas; however it is poor in the rural hinterland to the north of the city. The rural areas show a greater degree of flooding from the Areas Susceptible to Surface Water Flooding, compared to the Flood Map for Surface Water, as might be expected given comments received from the Environment Agency concerning the limitations of the data-sets. Clusters of known flood incidents have been grouped together to form several hotspots. However, there is a very poor correlation with the Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding. There are several datasets illustrating known incidents across Newcastle, each with differing levels of information associated with it; ranging from no information to detailed information. Where there is no information concerning the incidents, the hotspots delineated should be treated with caution since; the flood maps in these areas show limited flooding, the cause of the incident is unknown and there is the potential for duplicate entries. Improved reporting and investigations of flood incidents as required by the Flood and Water Management Act will help improve this aspect. The creation of a single dataset containing all surface water incidents detailing the cause, nature and mechanism of flooding would prove beneficial for Newcastle City Council. It has not been possible to investigate the poor correlation as part of the SWMP however an improved incident dataset and more detailed surface water modelling, may improve the correlation between the known incidents and flood maps. The majority of known incidents are dispersed and therefore cannot be grouped into a hotspot. One example is in the west of Newcastle, in Lemington and Westerhope. This area shows a number of known incidents but limited flooding from the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding. Further modelling could be beneficial to ascertain the mechanisms and causes for the flooding in this area and to determine whether the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding are correct. A smaller example is Byker which sits atop a hillside with a number of known incidents. Again the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding show little flooding and do not correlate with the known incident dataset and may also benefit from further modelling. Hotspots have been delineated beyond the Newcastle authority boundary. Those that do not influence any of the surface water risk areas within Newcastle will not be considered further but could be of use to the Council in the future for example for comparison purposes with neighbouring authorities. 2.2.2 Hotspot Prioritisation Whilst a great number of hotspots have been defined across Gateshead and Newcastle, the risk associated with them may be relatively low i.e. it may be an area of open parkland where no roads or properties would be affected. As such, it is appropriate to prioritise the hotspots with regard to the perceived risk associated with them. The prioritisation process should prove beneficial for the Partners to target funds in the areas of greatest risk. The prioritisation process has taken account of the following factors: AECOM Surface Water Management Plan 20
Capabilities on project: Water
- The number of known flood incidents within each hotspot, - The number of properties potentially at risk according to the Flood Map for Surface Water and Areas Susceptible to Surface Water2, - Critical Infrastructure at risk according to the Flood Map for Surface Water and Areas Susceptible to Surface Water, and - Development Sites (SLR, SHLAA and ELR) within hotspots. 2.2.2.1 Weightings Once each of the four factors had been calculated for each of the hotspots the factor was given a weighting in terms of its perceived importance (Table 2.1). The weightings were developed specifically for the study although were informed by experience of other SWMPs. Table 2.1: Weighting Applied to Prioritise Hotspots Factor Weighting Number of known flood incidents 10 Number of properties affected 0.1 Critical Infrastructure: Roads, Rail & Essential Infrastructure 5 Highly Vulnerable Infrastructure 3 More Vulnerable Infrastructure 2 Development Sites 5
The number of known incidents has been given the highest weighting (10) in light of these being flood incidents that have occurred. Therefore there is a flood risk that has happened previously and could happen again. The incidents have been pinpointed in terms of location and in some instances their causal mechanisms documented. In contrast the flood extents of the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding are based on hypothetical scenarios that may never materialise. The number of properties affected has been given a weighting of 0.1. This may appear low, however given the large numbers of properties that fall within the flood outlines of the Flood Map for Surface Water and Areas Susceptible to Surface Water giving it a higher weighting threatens to make all the other factors irrelevant. The number at properties at risk is based on the Flood Map for Surface Water 200 year greater than 0.1m deep and the Areas Susceptible to Surface Water Flooding Intermediate Susceptibility. These extents show the worst-case scenario for potential surface water flooding. Critical infrastructure has been sub-divided into three sub-categories; i) roads, rail and essential infrastructure, ii) highly vulnerable infrastructure and iii) more vulnerable infrastructure with weightings of 5, 3 and 2 respectively. Roads and rail were given a higher weighting in light of the crucial role they play in daily life and enabling the emergency services to operate. Examples of essential infrastructure include train stations and electricity stations/substations, highly vulnerable infrastructure includes police stations and ambulance stations and more vulnerable infrastructure includes schools, hospitals and STWs. Items of infrastructure have been counted and the count multiplied by the relevant weighting. Development sites have been included in the prioritisation process at the request of the Councils. Sites have been taken from the Strategic Land Review (SLR), SHLAA and ELR. These datasets are all given the same weighting. Where datasets exactly overlap or there is a duplicate entry, the development site in question is counted once. If the datasets overlap but are not the same shape and size they are counted individually.
2 Environment Agency guidance states that the Flood Map for Surface Water and Areas Susceptible to Surface Water should not be used to identify individual properties at risk. The assessment has used the number of properties as a guide to how many properties could be at risk, where larger numbers indicate a greater risk. AECOM Surface Water Management Plan 21
Capabilities on project: Water
The development sites represent ‘potential’ sites that may get developed and therefore there is the ‘potential’ for an increase in the number of properties at risk but also the opportunity to contribute to the management of flood risk in the wider area. The development sites in the hotspot area may not be at risk of surface water flooding but have been counted as they are in the vicinity of a risk area and could provide an opportunity to manage the risk. For each hotspot, the count for each of the four factors has been multiplied by its associated weighting and these weighted totals combined to give an overall score; the higher the score the greater the priority. The prioritisation process and particularly the weightings applied to each of the factors is extremely subjective, therefore a variety of different weightings were considered as part of the assessment to evaluate the impact. The outcome was that irrespective of the weightings applied the same hotspots repeatedly appeared at the top of the prioritised list, albeit it in slightly different orders for Newcastle. The prioritised list for Gateshead exhibited a greater degree of variation depending on the weightings applied. 2.2.2.2 Prioritised Hotspots – Gateshead Table 2.2 presents the top ten prioritised hotspots for Gateshead along with an approximate geographic location. Appendix A presents all of the hotspots for Gateshead and their priority matrix. Table 2.2: Top Ten Hotspots for Gateshead Ranking Hotspot Location 1 GH40 Team Valley 2 GH06 Ryton 3 GH04 Clara Vale 4 GH14 Blaydon =5 GH43 North Bensham =5 GH49 Heworth 7 GH30 Birtley 8 GH55 Blackhall Mill 9 GH27 Lamesley 10 GH42 Dunston
The River Team Integrated Modelling Study is currently being undertaken by Gateshead Council and the Environment Agency to investigate flood risk from urban drainage network and floodplain and linkages between then (i.e. the River Team, ordinary watercourses, surface water and sewer flooding). 2.2.2.3 Prioritised Hotspots – Newcastle Table 2.3 presents the top ten prioritised hotspots for Newcastle. Appendix B presents all of the hotspots for Newcastle and their priority matrix. AECOM Surface Water Management Plan 22
Capabilities on project: Water
Table 2.3: Top Ten Hotspots for Newcastle Ranking Hotspot Location 1 NH11 Gosforth 2 NH09 Brunton 3 NH14 Jesmond 4 NH16 City Centre - West 5 NH15 City Centre – Central and East 6 NH17 University & High Heaton 7 NH23 Walker 8 NH32 Denton Burn 9 NH19 Walkergate 10 NH31 Newburn
2.2.3 Observations As part of the Risk Assessment phase it has been possible to make a number of observations concerning the risk of surface water flooding across Gateshead and Newcastle; - 99 hotspots have been defined within the Gateshead and Newcastle authority areas. - The hotspots have been prioritised in terms of the risk and Tables 2.2 and 2.3 present the top ten for Gateshead and Newcastle respectively. It is recommended that if any of the Partners identify funding to undertake works to manage the risk of surface water flooding, these tables and Appendices A and B should be used to help identify the areas at greatest risk. - Known flood incidents do not always corroborate predictions concerning surface water flooding, particularly in Newcastle. - Many known flood incidents are a result of blockages in drainage systems. Maintenance of drainage systems; both natural and man-made, is critical to managing / limiting the impact of surface water flooding. In the current economic climate, maintenance budgets are likely to come under threat, if cuts are unavoidable it is essential that maintenance is targeted at appropriate times of the year, for example autumn when leaves fall off trees and often block road gullies. - Newcastle City Council should assimilate and endeavour to improve the quality of their flood incident database. - The Councils should develop their flood incident databases to be able to record additional information concerning flood incidents as and when they arise. 2.3 Phase 3: Options The Options phase has assessed 18 of the 99 hotspots that were identified by the Risk Assessment. The Partners identified nine hotspots in Gateshead and nine in Newcastle for consideration (Table 2.4). These 18 hotspots were selected based upon a number of factors including; the prioritisation process, the location of hotspots with regard to the Strategic Development Sites considered as part of the SWMP and the location of hotspots with regard to other development sites. AECOM Surface Water Management Plan 23
Capabilities on project: Water
Table 2.4: 18 Hotspots Identified by the Partners Gateshead Newcastle GH04 – Clara Vale NH09 – Brunton GH06 – Ryton NH11 – Gosforth GH14 - Blaydon NH15 – City Centre – Central and East GH15 - Blaydon NH16 – City Centre - West GH21 – Derwent Haugh NH19 – Walkergate GH26 – South of Lobley Hill NH23 – Walker North GH28 – Birtley NH24 – Walker Central GH42 – Dunston NH35 – Westerhope GH52 – Old Fold NH36 – Cowgate
As part of the Options work a data sheet has been prepared for each of the hotspots in Table 2.4, which sets out; - Whether or not Northumbrian Water is undertaking any works in the area and the data received from the Tyneside Sustainable Sewerage Study, - Any information that has been received from the Councils concerning historic flood incidents, - What is considered to be at risk within the hotspot, and - Potential measures that could be implemented to manage the risk. Each data sheet is accompanied by a figure illustrating locations where the measures could potentially be implemented and can be found in Appendices C and D for Gateshead and Newcastle respectively. 2.3.1 Northumbrian Water Data Capital Works Northumbrian Water provides each of the Councils with a list of capital works that they are undertaking. Northumbrian Water liaises with the Councils on a quarterly basis concerning updates to the list. Any relevant details have been reproduced for each hotspot. Tyneside Sustainable Sewerage Study The section highlights whether or not the Drainage Area within which the hotspot falls is a priority for Northumbrian Water. Northumbrian Water provided an extract from their Tyneside Sustainable Sewerage Study and details of their drainage areas covering Gateshead and Newcastle. 2.3.2 Council Records of Flooding This section of the data sheet sets out what information is held by the Council concerning flooding within the hotspot. GIS data has been provided by each of the Councils illustrating locations subject to flooding and in some instances details of the flooding. This information has been supplemented through a meeting with Council representatives at which each of the hotspots was discussed concerning the known risks and any additional data held by the Councils was subsequently provided. 2.3.3 Surface Water Flood Risk Based upon the Environment Agency’s Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding, this section sets out what is at risk of surface water flooding, highlighting areas where flooding may be deep and any critical infrastructure at risk. The areas highlighted as being at risk have been the target for the optioneering process. AECOM Surface Water Management Plan 24
Capabilities on project: Water
2.3.4 Managing the Risk The final section of the data sheet sets out the flood mitigation measures that have been reviewed concerning their feasibility for the hotspot in question and which are considered to be preferable. The tables setting out the screening process are subsequently followed by a narrative which describes locations where the measures could be implemented. These are illustrated on the figure accompanying the data sheet. List of Measures The approach to the Options phase identified a long list of mitigation measures. The long list is subsequently whittled down to a short list in each of the data sheets. In line with the approach to the Strategic Development Sites; those measures considered to be technically feasible are retained in the short list of measures, those that are not technically feasible are excluded. Identify Preferred Measures Preferred measures are subsequently identified. The appraisal is similar to that for the Strategic Development Sites; based on a Multi-Criteria Assessment (MCA) to determine which measures are preferable for each hotspot being considered. The following factors were considered by the MCA: - Technical – is measure technically possible to implement? - Economic – How does the cost of implementing the measure compare with the monetary benefits associated with it? - Social – how will the measure impact on the community? (this excludes factors such as flood risk being reduced but rather considers the loss of access to parks or roads if they acted as a store for flood water). - Environmental – will the measure provide wider environmental benefits? - Carbon Cost – is the measure and its implementation associated with a large carbon footprint? - Climate Change – can the measure be easily adapted to accommodate the impacts of climate change? - Sustainability – is it considered to be a sustainable approach? For example, a measure involving large quantities of concrete may not be considered to be particularly sustainable. Each factor has been scored with the following relative indicators (as set out in the guidance): - -2 – severely negative outcome - -1 – moderately negative outcome - 0 – neutral outcome - +1 – moderately positive outcome, or - +2 – strongly positive outcome The scoring for each factor has been based on engineering judgement. Each factor has had the same weighting applied as was the case for the Strategic Development Sites and the scores summed for each measure. The higher scoring measures are considered to be preferable. A number of measures from the short list are able to provide a solution for the hotspots. AECOM Surface Water Management Plan 25
Capabilities on project: Water
2.3.5 Taking Action - Gateshead In light of the work that has been undertaken for the 18 hotspots it is considered worthwhile providing the Partners with an indication of where they should take action, if funding were available. Across Gateshead many of the extreme flood outlines are corroborated by records indicating that flooding has occurred. Equally most flood records date from 2000, 2006 and 2008 suggesting that during extreme rainfall events several areas could all be affected. As such it makes it difficult to prioritise one hotspot over the others since several are predicted to be affected during extreme events by hydraulic modelling and have been observed to flood. One hotspot (of the nine reviewed) has a greater concentration of known flood events, has a Northumbrian Water capital scheme underway and is going to be re-developed in the near future. This is hotspot GH42, Dunston, where the Ravensworth Road area has experienced five flood incidents since 2000, four of which have been in the last four years. Northumbrian Water have a capital scheme to improve the sewer networks which is designed to tie in with redevelopment of the Tower Court area which itself offers opportunities to manage surface water runoff from the site and wider area. The flood risk along Ravensworth Road is associated with its proximity to the River Team. At this location the River Team is tidally influenced therefore during high tides and flood flows water levels in the river will prevent the sewer system discharging. As a result the sewers surcharge and flood out onto the roads. The sewers will always be subject to surcharging during high water levels in the river. Northumbrian Water expects a 1 in 20 year standard for existing drainage, whereas the guide for new development will be for a 1 in 30 year standard. Northumbrian Water would however seek the provision of a 1 in 40 year standard as the norm except where local conditions would prevent this. In this circumstance the best standard possible would need to be provided. Therefore as part of the re-development, there is the opportunity for Gateshead Council and other Partners to provide a mitigation measure to address more extreme events that the sewers are not designed to cope with. If funding were available an overland flow path could be created to allow excess runoff to flow into the River Team. Due to the nature of the local topography, surface water currently collects at the northern end of Ravensworth Road, therefore a formal overland channel could be created to allow this water to drain north east, across Clockmill Road and into the River Team. The photo to the right is taken from the River Team, looking south west across Clockmill Road, towards Ravensworth Road. As part of the design it would be important to avoid a low point being created along the bank of the River Team which would permit extreme tidal levels to escape from the channel and affect Ravensworth Road. Such a scheme could be costly and take a considerable period of time to implement. Two potential “quick wins” could be achieved in hotspots GH28; Birtley and GH52; Old Fold. A site visit to the ELR site at Birtley, off Durham Road, found that the western extent of the site has naturally developed into a wetland area supporting a variety of flora and fauna which favour wet conditions (see photo right). Gateshead Council could exclude this area from development and utilise it as multifunctional green space into which excess runoff could be channelled and biodiversity benefits achieved. An area of green space also exists at Old Fold between Green Lane Gardens and the A184 which has been subject to flooding in the past. Utilising this AECOM Surface Water Management Plan 26
Capabilities on project: Water
green space to hold water in either a storage area or swale could provide benefits to the A184 which is a critical transport route and the surrounding properties. Gateshead Council may be able to implement this through links to the Neighbourhood Plan for Brandling. 2.3.6 Taking Action - Newcastle In the case of Newcastle, no one hotspot stands out from the others (of the nine reviewed) since they cover quite different spatial scales and known flood records do not always corroborate the Flood Map for Surface Water or Areas Susceptible to Surface Water Flooding. The Ouseburn, an Environment Agency Main River, is a significant issue for Newcastle in that it presents a flood risk in its own right but it also impedes natural and man-made systems that drain into it causing surface water flooding in surrounding areas. Newcastle City Council has received funding via the Local Levy to review the potential of the Ouseburn’s tributaries to store water thereby delaying the speed with which water gets into the Ouseburn and the risk it poses. Newbiggin Burn and Devils Burn/Craghall Dene are two tributaries of the Ouseburn that flow through hotspots NH09 and NH11 respectively, therefore it may be possible to identify opportunities to manage the flood risk from the Ouseburn and the surface water risk within the hotspots. Structures crossing the Burns/Denes ought to be recorded in an Asset Register and desk studies undertaken, building on the work presented in Appendix D to evaluate the potential that the Burns possess. Quick wins that Newcastle City Council could implement could relate to hotspots NH23 and NH24 in Walker. Waverdale Avenue (NH23) is a key transport route which was affected by flooding in 2010 (photo right) and is predicted to be affected by deep flooding in the 3.33% and 0.5% AEP events. Multifunctional green space is located either site of the low spot on Waverdale Avenue where water would collect therefore it may be a relatively straight forward operation to drop the kerbing on either side of the road to allow excess surface water to flow overland into the green space. A school is being built off Waverdale Avenue therefore management of surface water could also provide benefits for the school assuming it is too late for measures to be incorporated into the school development. In hotspot NH24 Walker Park is multifunctional green space that should be used to mange surface water. Newcastle City Council could work with the developers of SHLAA sites in the area to use the park to store surface water during extreme events. 2.3.7 Next Steps As part of the Options phase a variety of flood mitigation measures were identified and appraised to evaluate their potential to manage the risk of surface water flooding in each of the 18 hotspots. This produced broad, high-level measures by which the risk of surface water flooding could be managed. The details of the Options phase are only intended to indicate the elements of a possible solution that could be implemented to manage surface water and provide a starting point for further investigations should the Partners wish to take action to address the risk of surface water flooding. 2.4 Phase 4: Implementation and Review The final phase of the SWMP is the collation of the information from the first three phases and the production of an Action Plan for managing surface water. Chapter 3 of this document sets out the Key Findings of the study and has developed an Action Plan for the Partners to implement as they seek to manage the risk of surface water flooding across Gateshead and Newcastle. The 18 hotspots assessed as part of the Options phase have been used as case studies from which to draw out broad actions that are applicable to the whole of Gateshead and Newcastle. AECOM Surface Water Management Plan 27
Capabilities on project: Water
It will subsequently be up to the Partners to implement the Action Plan to manage and mitigate the risk of surface water flooding across Gateshead and Newcastle subject to funding restrictions. As lead Partner, it will be the Councils responsibility to monitor and review the implementation of the Action Plan. The SWMP is a living document and it is recommended that the Partnership continues to work together after the completion of the SWMP to discuss the implementation of the proposed actions. The SWMP should be reviewed and updated on a regular basis, but there are circumstances which might trigger a review or an update sooner. These may include the occurrence of a flood incident or additional data becoming available, which may alter the understanding of risk within the study area. A generic SWMP flow chart is illustrated in Figure 2.5. It should be noted that given the changing nature of SWMPs, the process is an iterative one, which should be monitored on a continual basis. For example, it may be that one of the 18 hotspots which have been considered at a strategic level in this document is given further consideration at some point in the future, in which case an intermediate or detailed SWMP may be undertaken for that specific area. Figure 2.7: Iterative Nature of SWMPs
Strategic Assessment Partnership/Steering Group
Implemetation and Preparation Risk Assessment Option Appraisal Monitoring Plan Implementation and Monitoring
Intermediate Assessment
Re-appraise Risk Revise Implemetation and Re-appraise options Assessment Monitoring Plan
Detailed Assessment Risk Assessment Re-appraise Revise Implemetation and (with modelling) options Monitoring Plan Key Findings & Action Plan AECOM Surface Water Management Plan 29
Capabilities on project: Water
3 Key Findings & Action Plan
In light of the Risk Assessment and Optioneering work that has been undertaken for Gateshead and Newcastle, it is possible to identify a number of key findings for further consideration by the Partners. 3.1 Surface Water Flood Risk
Z Surface water flood risk exists in many parts of Gateshead and Newcastle. Areas at risk have been identified and prioritised in terms of the risk (Appendices A and B).
Z Team Valley Trading Estate (GH40) is at the greatest risk of surface water flooding in Gateshead.
Z The interaction of natural, and man-made, surface water drainage systems with the Ouseburn poses the greatest risk in Newcastle. Key areas affected include Brunton (NH09) and Gosforth (NH11).
Z Known flood incidents do not always corroborate predictions concerning surface water flooding, particularly in Newcastle. Newcastle City Council should assimilate and endeavour to improve the quality of their flood incident database which may improve the correlation with future revisions of the Flood Map for Surface Water.
Z Many known flood incidents are a result of blockages. Maintenance of drainage systems; both natural and man-made, is critical to managing / limiting the impact of surface water flooding. In the current economic climate, maintenance budgets are likely to come under threat, if cuts are unavoidable it is essential that maintenance is targeted at appropriate times of the year, for example autumn when leaves fall off trees and often block road gullies.
Z The Councils should develop their flood incident databases to be able to record additional information concerning flood incidents as and when they arise. AECOM Surface Water Management Plan 30
Capabilities on project: Water
3.2 Managing Surface Water
Z In order to realise the Councils’ growth aspirations it is essential that surface water is removed from all of the combined sewer systems draining to Howdon STW including those that serve Gateshead and Newcastle.
Z Development presents the best opportunities to remove surface water from the combined sewer systems and manage the risk of surface water flooding.
Z Re-development that separates surface water from the combined sewer system will increase the ability of the system to accept foul flows from new development.
Z Managing surface water on site will limit the risk of sewers surcharging and causing flooding and avoid passing the risk of flooding elsewhere.
Z The Councils should require developers to; not only address runoff from their site but the potential benefits that can be achieved for the wider area, and to utilise multifunctional green space to manage surface water runoff.
Z Several development sites that provide opportunities to manage the risk of surface water flooding have been identified (Table 3.1)
Z If development sites in areas at risk of surface water flooding are unlikely to come forward in the planning process, the Partners ought to consider using the sites to provide formal surface water management. For example, through the creation of wetlands water quality benefits and green infrastructure opportunities could also be realised.
Z There are many areas where development does not offer opportunities to manage the risk of surface water flooding. In such circumstances the Partners will need to take action themselves, through the SWMP process, to manage the risk. This would usually be in the form of retro-fit schemes.
Z The Partners can also encourage and support individuals / communities to take action to protect themselves from surface water flooding (see Section 4.1).
Z The Councils should consider the potential for surface water management when undertaking highways schemes such as re-grading roads, to manage and identify strategic overland flow routes through urbanised areas.
Z The Councils consult Northumbrian Water concerning the appropriateness of development within 100m of the DG5 sewer flooding records. AECOM Surface Water Management Plan 31
Capabilities on project: Water
Table 3.1 presents those development sites that have been identified as part of the Options phase that offer opportunities to manage the risk of surface water flooding in and around the 18 hotspots that have been assessed. Table 3.1: Development sites that provide opportunities to manage the risk of surface water flooding Reference SHLAA / ELR / SLR Hotspot Newcastle / Gateshead G118 SHLAA GH04 Gateshead G494 ELR GH14 Gateshead G494 ELR GH15 Gateshead G108 ELR GH21 Gateshead G288 SHLAA GH21 Gateshead G144 SHLAA GH21 Gateshead G145 SHLAA GH21 Gateshead 62 SLR GH26 Gateshead G269 ELR GH28 Gateshead G66 SHLAA GH42 Gateshead G82 SHLAA GH52 Gateshead G1 SHLAA GH52 Gateshead 2641 SHLAA NH09 Newcastle 2642 SHLAA NH09 Newcastle 4928 SLR NH09 Newcastle 4820 SLR NH09 Newcastle 4951 SLR NH09 Newcastle 4930 SLR NH09 Newcastle 4827 SLR NH09 Newcastle 4708 SHLAA NH11 Newcastle 4287 SHLAA NH11 Newcastle 4402 SHLAA NH11 Newcastle 4853 SHLAA NH11 Newcastle 1461 ELR NH15 Newcastle 1313 SHLAA NH15 Newcastle 1313 ELR NH16 Newcastle 1328 ELR NH16 Newcastle 4725 SHLAA NH16 Newcastle 4654 SHLAA NH19 Newcastle 1009 SHLAA NH19 Newcastle 4014 SHLAA NH19 Newcastle 4571 SHLAA NH19 Newcastle 1100 SHLAA NH23 Newcastle 4137 ELR NH23 Newcastle 4732 SHLAA NH24 Newcastle 4252 SHLAA NH24 Newcastle 1129 SHLAA NH24 Newcastle 4249 SHLAA NH24 Newcastle 4250 SHLAA NH24 Newcastle 3004 SHLAA NH35 Newcastle 4940 SLR NH35 Newcastle 4207 SHLAA NH36 Newcastle 4088 SHLAA NH36 Newcastle 4602 SHLAA NH36 Newcastle 4429 SHLAA NH36 Newcastle AECOM Surface Water Management Plan 32
Capabilities on project: Water
3.3 Action Plan An Action Plan has been developed as part of Phase 4 of the SWMP (Table 3.4). The Action Plan provides a list of actions by which the Partners (the Councils, Environment Agency and Northumbrian Water) can manage and mitigate surface water flooding. The actions within the plan have been divided into sub categories (Table 3.2) to allow for easier implementation. Table 3. 2: Action Plan Categories Action Type Definition Flood and Water Management Act Actions that must be undertaken in order to comply with the Flood and Water Actions Management Act. Partnership Actions Actions requiring the Partners to work together. Policy Actions Actions to incorporate into future spatial planning and/or development controls. Highways Actions Actions in relation to roads and highways. Surface Water Risk Actions Actions to manage the risk of surface water flooding. Howdon STW Actions Actions to ensure that Howdon STW does not constrain development.
3.3.1 Flood & Water Management Act Requirements
The Flood and Water Management Act gives new powers to help manage local flood risk in a more strategic way whilst also placing a duty on key Partners to co-operate. The Action Plan (Table 3.4) lists the actions required, including the timescales and who is responsible for implementation, to comply with the Flood and Water Management Act and the specific tasks necessary to meet them. The following describes two requirements of the Flood & Water Management Act that have been incorporated into the Action Plan. Data Asset Register
The Flood and Water Management Act states that all Lead Local Flood Authorities must establish and maintain:
- a register of structures or features which, in the opinion of the authority, are likely to have a significant effect on flood risk in its area, and
- a record of information about each of those structures or features, including information about ownership and state of repair. An Asset Register is being prepared using appropriate guidance from DEFRA and the experiences of other LLFA’s. Investigate Flood Incidents
The Flood and Water Management Act also states that Lead Local Flood Authorities will investigate flooding incidents in its area (where appropriate or necessary) to identify which authorities have relevant flood risk management functions and what they have done or intend to do. The Lead Local Flood Authority will then be required to publish the results of any investigation, and notify any relevant authorities. In order to do so, the Councils will initially need to be made aware of any reported flood incidents. Flooding could be reported to the Councils by members of the public, private organisations, the Environment Agency or Northumbrian Water. As such it would be appropriate for the Councils to maintain a register of flood incidents. It would also be practical for this to be integrated with the Asset Register so that assets responsible for flooding could be linked to the events. In many instances, the flooding will not fall under the jurisdiction of the Environment Agency or Northumbrian Water therefore it will fall to the Councils to investigate the matter. In such circumstances a quick response will be essential to ensure that details of the flood extent are accurately recorded (through site photographs and survey if appropriate) and eye witness accounts are documented before the passage of time has the effect of over- or under-exaggerating the events. Table 3.3 sets out the Flood Incident Register that the Councils have started using. AECOM Surface Water Management Plan 33
Capabilities on project: Water
Table 3.3: Flood Incident Register used by the Councils
In addition to details of the flooding itself it is extremely valuable to have information concerning the causative mechanisms of flooding. Rain data can easily be obtained from the Environment Agency, or potentially Northumbrian Water, and details of the rainfall causing the flooding analysed. It is a quick procedure to use the Flood Estimation Handbook CD-ROM to estimate the rarity, or probability, of a rainfall event, which can subsequently be used to evaluate whether or not the local drainage systems could be expected to accommodate the event without flooding occurring. The proximity of a rain gauge to the flood event may influence the reliability of the rarity calculated. All Partners will need to be involved in these arrangements, so as to ensure that the flooding information is both comprehensive and suitable for supporting the identification of priority in any flood risk management schemes to be implemented. 3.4 Going Forward
The Action Plan should remain as a ‘living’ document. It should be noted that once the outcome of investment decisions is known, and once Partners have tried to secure funding to implement their elements of the plan, there may be a requirement to revise the Action Plan. It is therefore important that Partners continue to work together after the SWMP has been completed. AECOM Surface Water Management Plan 34
Capabilities on project: Water
Table 3.4: Action Plan for the Gateshead and Newcastle Partners (lead in bold) Timetable for Ref Type of Action Action Implementation
Flood & Water Newcastle City Council to improve GIS data concerning known surface water 1 Newcastle City Council 0-6 months Management Act incidents.
Flood & Water Undertake appropriate investigations into flood incidents and formalise the 2 Councils 0-6 months Management Act recording and reporting of them.
Councils Continue to investigate causes of flooding and the standards of service in Flood & Water 3 relation to problems, followed by appropriate remedial works where funding is Northumbrian Water Ongoing Management Act available. Environment Agency
Flood & Water Develop Asset Data Register. Including the identification of third party assets 4 Councils December 2012 Management Act deemed to affect flooding.
In accordance with Flood & Water 5 Establish SuDS Approval Body. Councils DEFRA / Environment Management Act Agency timescales
Councils 6 Partnership Partners to continue to work together so as to better manage surface water risks. Northumbrian Water Ongoing Environment Agency
Councils Partners to ensure that natural and man-made drainage systems are adequately 7 Partnership maintained within financial constraints so that the risk of flooding is appropriately Northumbrian Water Ongoing managed. Environment Agency
Councils to consult with Northumbrian Water concerning development within Councils 8 Partnership Ongoing 100m of known sewer flooding locations. Northumbrian Water
Councils Surface water to be removed from combined sewer systems. SuDS to be Pre-development 9 Policy implemented by developers to manage surface water rather than disposing of it Northumbrian Water to the combined sewer system. Ongoing Environment Agency
Councils Pre-development 10 Policy Surface water runoff should be managed at source avoiding disposal to a public sewer where possible. Source control measures such as green roofs, Northumbrian Water 0-12 months AECOM Surface Water Management Plan 35
Capabilities on project: Water Partners (lead in bold) Timetable for Ref Type of Action Action Implementation
permeable paving, storage and rainwater harvesting to be required. Environment Agency
Councils Development should implement pollution control as appropriate to help improve Pre-development 11 Policy Northumbrian Water water quality and work towards achieving WFD requirements. 0-12 months Environment Agency
Councils Runoff rates should not exceed Greenfield wherever possible. Any re- Pre-development 12 Policy development should reduce runoff by a minimum of 50% of existing brownfield Northumbrian Water runoff*. 0-12 months Environment Agency
Councils Runoff up to and including the 1% AEP event (1 in 100 year event) should be Pre-development 13 Policy Northumbrian Water managed on site where possible. 0-12 months Environment Agency
Councils Developers should be required to set part of their site aside for surface water Pre-development 14 Policy Northumbrian Water management and to supplement green infrastructure networks. 0-12 months Environment Agency
All new car parks to comprise permeable paving (including resurfacing of 15 Policy Councils Ongoing existing car parks and domestic parking areas).
Developers to utilise existing multifunctional space to manage excess surface 16 Policy Councils Ongoing water runoff.
Highway maintenance schemes to consider the potential of road re-regarding and provision of street architecture such as kerbing to provide surface water 17 Highways Councils Ongoing management such as storing water in the road or channelling it overland to areas of multifunctional space or formal storage areas.
Highway authorities to review the need for highway drainage to go to a public 18 Highways sewer before agreeing to adopt new roads. Appropriate SuDS systems should Councils Ongoing be used as a priority over discharging to the combined sewer system.
Councils Partners to consider further studies to review surface water flood risk in areas Surface Water 19 identified as being at the greatest risk in and around Strategic Development Northumbrian Water 0-2 years Risk Actions Sites. Environment Agency
20 Surface Water Partners to consider further studies to review surface water flood risk in the Councils 0-2 years AECOM Surface Water Management Plan 36
Capabilities on project: Water Partners (lead in bold) Timetable for Ref Type of Action Action Implementation
Risk Actions prioritised hotpots. Northumbrian Water Environment Agency
Complete Sustainable Sewerage Study and Implement Tools and Techniques 21 Howdon STW Northumbrian Water 0-5 years developed to remove surface water from the combined sewer system.
Monitor house building across Howdon STW catchment area in combination with 22 Howdon STW Councils Ongoing North and South Tyneside and Northumberland Councils.
23 Howdon STW Monitor performance of Howdon STW. Environment Agency Ongoing
24 Howdon STW Develop surface water reduction policies. Councils 0-12 months
Councils Review success of actions to reduce volume of surface water reaching Howdon 25 Howdon STW Northumbrian Water 2017 STW. Environment Agency
Councils Partners to establish a Working Group to continue after the SWMP to review and 26 Howdon STW monitor the situation at Howdon STW and inform and update the Infrastructure Northumbrian Water October 2011 Delivery Plan for the Core Strategy. Environment Agency
27 Howdon STW Complete Asset Management Plan for Howdon STW. Northumbrian Water 0-2 years
*The target of 50% reduction in runoff, was discussed by the Partners and is considered to be an achievable target. Funding for Surface Water Management AECOM Surface Water Management Plan 38
Capabilities on project: Water
4 Funding for Surface Water Management
4.1 Introduction The Environment Agency has calculated that one million people in England and Wales are vulnerable to surface water flooding with a further 2.8 million properties susceptible to surface water flooding alone. Average flood damage costs are currently in the region of £1 billion per year, but these costs could rise to as much as £27 billion by 2080. At a time when the Government is calling for budget reductions, national government is unlikely to be a primary source of funding for measures by which the risk of surface water flooding can be managed. Given the national spending constraints, and due to the large and growing flood management problem, it is likely that local sources of funding will become increasingly important. The Pitt Review said that those that will benefit from flood defence might wish to contribute to costs: “The Review does not believe that it is unreasonable, therefore, for funding to come from sources other than Government, such as a local authorities, business, environmental organisations or local community groups”. The following section provides a discussion of potential means by which measures identified in the SWMP could be funded. 4.2 Local Authorities
Currently, Local Authorities receive an allocation from central government through the Revenue Support Grant, but this is not ring-fenced and does not have to be spent on flood risk. Alternatively, local authorities can use their own funds to tackle flood risk, choosing to follow the example of Gloucestershire County Council in raising additional council tax specifically to manage flood risk. Sources of local funding could include:
- Local authority spending (either from the revenue support grant or through a council tax levy);
- Voluntary contributions from local businesses or individuals; and,
- Community funding (such as though Business Improvement Districts or the Private Streetworks code)
Local Authorities can apply for a grant for capital investment from the Environment Agency to create new or improved flood risk and coastal erosion management infrastructure. The Flood and Coastal Resilience Partnership Funding3 is a new approach whereby Government funding is allocated to projects based on the number of households protected and other benefits which can be achieved. The scheme aims to encourage greater partnership working between the authorities, sectors, communities and others that have an interest in tackling flood and coastal erosion over the long term. The amount of funding provided by the Government, to be spent by March 2015 is at least £2.1 billion. The programme of schemes which will go ahead is prepared by the Environment Agency, which will be approved by the Regional Flood and Coastal Committees in each part of the country, and includes Local Authority representatives. This allows greater local influence on which schemes proceed each year. The priority of projects is risk based and relates to the amount of damages which will be avoided. Funding may also be raised by Local Authorities by means of Local Levy, or by different groups and sectors which have the ability to pay. The Local Levy is a way by which the Regional Flood and Coastal Committee can raise money to help pay for additional flood and coastal erosion risk management. It is voted and paid for by the County and Local Authority. The Environment Agency is working with Gateshead Council, Newcastle City Council, Northumbrian Water and local communities to reduce the risk of flooding to homes and businesses. The scheme has so far included raising the height of two bridges across the Ouseburn, reviewing the drainage system in Gateshead and Newcastle and working with residents to keep local streams free from rubbish and blockages.
3 http://archive.defra.gov.uk/environment/flooding/funding/documents/flood-coastal-resilience-intro-guide.pdf AECOM Surface Water Management Plan 39
Capabilities on project: Water
Revenue and non-grant eligible expenditure by Local Authorities is supported by formula grant from Communities and Local Government, but it is not ring fenced for flood and coastal risk management. Individual authorities can decide how much to spend, subject to limits on overall budgets and the need for investment on other priorities. Additional income can also be secured through the planning system and from contributions secured from major beneficiaries. Local Authorities and communities already have a range of options available to them to help pay for local schemes that do not meet national priorities but nevertheless deliver significant benefits to local communities. Such local funding mechanisms could range from the use of existing Local Authority prudential borrowing and wellbeing powers, the business improvement district model or even increases in council tax precepts, where these are affordable and in the best interest of local communities. Other, new and alternative, funding sources are available from a range of organisations. These include:
- Section 106 agreements, local tariffs, supplementary planning documents and any future community infrastructure levy, subject to its introduction
- Local business rates including ’business rate supplements‘ and council taxes including specific precepts and ‘special expenses’, plus fees and charges, where appropriate and affordable
- Local activities that can achieve flooding and coastal erosion benefits as a secondary outcome to their primary purpose of securing community benefit and facilitating economic growth and sustainability. These activities would include those associated with the local environment, land management, highways management, community infrastructure management, recreation, tourism, wealth creation and regeneration plans
- Funding could be sourced from the Highways Capital and Maintenance Programme by working in close coordination with highways authorities during works during maintenance works and new installations. 4.3 Business In Hereford; the supermarket chain Asda contributed £2m as part of the planning conditions for a supermarket in the town, in addition to constructing 440m of flood defences. The total cost of the scheme was £7.5m and it provides protection to 196 properties including 25 listed buildings. The Leeds City Flood Alleviation project will increase the level of protection to Leeds city centre but makes a relatively low contribution to reducing flood risk for households. However, the proposed project is likely to enable significant economic and financial benefits for the local and regional business, commercial and development/regeneration sectors. The Environment Agency considers that these benefits are sufficient to justify a contribution of at least £50m towards the £178m scheme’s total cost. Discussions, consultations and negotiations are on-going between the Environment Agency and the City Council on how this value of contribution can be realised to secure the proposed benefits to the city. 4.4 Community Self Help The Big Society forms a part of the legislative programme of the Conservative-Liberal Democrat Coalition Agreement. The aim of the Big Society is to create a climate that empowers local people and communities, building a Big Society that will take power away from politicians and give it to the people. The following sections present examples of where local communities have pulled together to address the risk of flooding. 4.4.1 The Hanneys Flood Group
The villages of East and West Hanney, Oxfordshire were affected by flooding during 2007. Many residents felt that despite the unusual weather actions could have been taken to reduce the consequences of such flood events. The Hanneys Flood Group was set up to improve the ability of the community to accommodate similar events in the future. The Hanneys Flood Group consists of volunteers working for the benefit of the community and has members from the East Hanney and West Hanney Parish Council and Oxfordshire County Council and works closely with the Environment Agency, Oxfordshire Highways, Local AECOM Surface Water Management Plan 40
Capabilities on project: Water
Landowners, Vale of White Horse District Council Emergency Response Officer and the Vale of White Horse District Council Land Drainage Engineer. Volunteers cleared weeds from a local brook, increasing the brook’s capacity, and also constructed a flood defence bank and footpath. The Environment Agency provided soil, the hire of two mini-excavators and two dump trucks. The Local Authority paid for materials used to help stabilise the new bank. 4.4.2 Bucklebury Flood Alleviation Scheme
A community-led partnership formed by Bucklebury residents, the Environment Agency and West Berkshire Council is the driving force behind a flood alleviation scheme for the village of Bucklebury, Berkshire. The villagers set up a Community Interest Company (CIC) after the floods of 2007, and took an active part in looking into how future flooding could be prevented. Funded by the Regional Flood Defence Committee with contributions from the villagers and West Berkshire Council, the scheme will protect 25 homes and the village hall from future flooding. The overall cost of the scheme is £600,000; of which £65,000 had been raised from residents alone, while grants from West Berkshire Council, Bucklebury Parish Council and the Thames Regional Flood Defence Committee would make up a further £550,000 towards the alleviation works. The flood alleviation scheme includes building flood bunds, digging a bypass channel and developing a new ford to divert flood flows around the village. It also includes works to ensure the flood risk is not increased downstream in Stanford Dingley. The CIC approached the Environment Agency and West Berkshire Council to discuss various strategies, and just over three years later, a new flood alleviation scheme was proposed for the village. 4.4.3 Appleby
This scheme (and another in Sandside, South Lakeland) was jointly conceived and administrated by the Environment Agency and Eden District Council (South Lakeland District Council for Sandside). It formed part of the national Defra £500,000 Pilot Flood Resilience project where local authorities and the Environment Agency were encouraged to work together in different ways to promote a resilience scheme. £90,000 and £80,000 of grant money was received by Eden and South Lakeland Councils respectively, directly from Defra. This arrangement meant that the Councils could use their grant distribution powers to fund individual property protection schemes. The average amount of grant issued to the 46 properties that took part was approximately £1,300. The property owners were expected to fund any work in excess of the grant available for their particular property. Approximately 26 of the properties that took part in the Appleby scheme benefited from their defences in the November 2009 flooding. They would have flooded if their resilience scheme funded defences had not been in place. 4.4.4 Bawdsey
In 1997 a major storm caused the already vulnerable coastline at East Lane, Bawdsey in Suffolk to erode severely. This retreating coastline posed an immediate threat to three coastal properties, including a Grade I listed Martello Tower. Due to insufficient priority, Suffolk Coastal District Council struggled to justify grant aid to fund a complete scheme at East Lane. This led to a series of emergency works along the District Council and Environment Agency frontages to limit the damage caused primarily from winter storms. In 2007 a group of local landowners and residents formed East Lane Trust, a “not-for-profit” charitable organisation to raise £2.2m to implement a coastal protection and flood defence scheme for the 250m section of coast. The money was raised by selling plots of land in nearby villages. In 2007, the government granted special permission to allow 26 homes to be built on the plots which were not in the Local Plan as being available for residential development. The money raised was given to the District Council to commission a sustainable coast protection scheme which was completed in summer 2009. It is thought to be the first privately funded coastal protection scheme since the enactment of the Coast Protection Act in 1949. The scheme highlights that, through effective co-operation between local communities and the responsible authorities, common goals can be achieved. AECOM Surface Water Management Plan 41
Capabilities on project: Water
4.4.5 The Big Society
The Big Society was the flagship policy idea of the 2010 UK Conservative Party general election manifesto and now forms a part of the legislative programme of the Conservative-Liberal Democrat Coalition Agreement. The aim of the Big Society is to create a climate that empowers local people and communities, building a big society that will take power away from politicians and give it to the people. With regards to planning, building and the environment4 it is the Governments belief that wherever possible, planning decisions should be made at the local level whereby councils have the freedom to make their own planning decisions in the best interest of the local area. The desired effect of the change in power will be to place the council and community at the heart of the planning process which will promote incentives to ensure communities benefit from new homes, matched with new jobs and investment through sustainable development. This overhaul of the current planning policy will allow councils and communities to have more control and flexibility over the planning decision to ensure a faster leaner planning process. 4.5 Resistance and Resilience Measures
Property owners can mitigate the risk of flooding by means of resistance, resilience and maintenance measures. It should be noted that the use of such measures are dependent on a site by site basis in terms of their suitability and the measures should not increase the risk of flooding to the surrounding area. 4.5.1 Resistance Measures
Flood resistance aims to prevent entry of water or minimise the amount of water that may enter a building where there is flooding outside. In considering these measures it will be necessary to consider the ability of the external fabric of the building to withstand water pressure as well as impacts from debris transported by flood water. It is also necessary to consider each property on an individual basis since the combination of both surface and fluvial flooding may often go hand in hand. The use of resistance measure requires the occupant to be present before a flooding event, which may not be suitable where surface water flooding is the sole flooding mechanism, but is suitable when combined with fluvial flooding and there is adequate warning available. - Non-return valves can be fitted to drains and water inlets/outlet pipes to prevent waste water from flowing into the property. This is a relatively easy method which can be used to retrofit existing properties to provide effective flood resistance. - Sandbags can be used to build temporary defenses to help prevent flood water entering a building. This is a low cost and effective solution for flood depths up to 300mm. A place to store sandbags is required along with the need for suitable warning (Environment Agency Floodline5). Commercial properties may also need to train staff in the effective deployment of sandbags. - Flood boards can be fitted to external doorways and windows to help keep flood water out. A place to store flood boards is required along with the need for suitable warning. Commercial properties may need to train staff in their effective deployment. This is a relatively effective method which can be used to retrofit existing properties to provide effective resistance. The fitting of flood boards would incur a higher cost in comparison to the use of sandbags. - Temporary and demountable flood defences around a property can help prevent flood water from entering a building, as well as protecting against water pressure and debris transported by flood water. These methods can theoretically be deployed by a single person; however this would require training as well as adequate warning. This would be a high cost solution in comparison to those above.
4 http://www.communities.gov.uk/planningandbuilding/about/ 5 http://www.environment-agency.gov.uk/homeandleisure/floods/38289.aspx AECOM Surface Water Management Plan 42
Capabilities on project: Water
4.5.2 Resilience Measures
Flood resilience aims to reduce the consequences of flooding in the event that flood water enters the building. Flood resilience measures help to facilitate recovery from the effects of flooding sooner than would otherwise be the case. Methods that could be applied to both commercial and residential properties include: - Locate electrical controls, cables and appliances at a higher level than normal. This would be appropriate for any new build, during renovation of existing developments or repair following a flood event. - Use water resistant plasterboard or horizontal plasterboard, this can be retrofitted into existing buildings as well as new development along with the use of waterproof bricks. - Locate ventilation higher than normal level, this can be retrofitted into existing buildings as well as used in new development. - Landscape external areas to divert flood water away from the building but importantly allows flood water to drain away following a flood event. This method of resilience can be retrofitted into existing development, and should be incorporated into the design of new development. 4.5.3 Maintenance
Properties with surface water outfalls into a local watercourse should regularly inspect the outfall to ensure that they are not blocked/flap valves are operating, and that the watercourse is free from debris, which may otherwise compromise the discharge of surface water from a development. Regular inspection of drains and gullies on the roadside can help identify blockages or problems with the drainage system and should be reported to the Local Authority for maintenance. Regular inspection and maintenance of resistant and resilience measures incorporated into a building is essential to ensure their effectiveness when deployed. Furthermore information and advice on flood resilience and resistance and products can be found at: - Environment Agency website : Preparing Your Property for Flooding [http://www.environment- agency.gov.uk/homeandleisure/floods/31644.aspx] - National Flood Forum website [http://www.floodforum.org.uk/] - Communities and Local Government website: Improving the Flood Performance of New Buildings: Flood Resilient Construction [http://www.communities.gov.uk/publications/planningandbuilding/improvingflood] Summary AECOM Surface Water Management Plan 44
Capabilities on project: Water
5 Summary
The NewcastleGateshead SWMP is a high level, strategic document which serves as a starting point for the Partners to address the risk of surface water flooding across Gateshead and Newcastle and contribute robust evidence base to support the LDF, including the Core Strategy. The SWMP has been produced as a series of documents, this one has identified areas at risk of surface water flooding across Gateshead and Newcastle. The work undertaken has reviewed existing data to identify areas at risk of surface water flooding which have been called “hotspots”. The hotspots were subsequently prioritised to determine which hotspots were associated with the greatest risk and 18 of them reviewed to evaluate potential means by which the risk of surface water flooding could be managed. These 18 hotspots have then been used as case studies from which to draw out surface water issues relevant to Gateshead and Newcastle. 5.1 Surface Water Principles In light of the work undertaken as part of the SWMP, the following surface water principles have been developed for Gateshead and Newcastle.
Z Surface water should be removed from the combined sewer system to free up headroom (spare capacity) at Howdon STW.
Z Surface water runoff to be managed at source (avoid disposal to public sewer systems wherever possible).
Z Runoff rates should not exceed Greenfield wherever possible.
Z Any redevelopment of brownfield land should reduce runoff by a minimum of 50%.
Z Runoff up to and including the 1% AEP event (1 in 100 year) should be managed on site where possible.
Z Measures of source control should be required for development sites.
Z Developers should be required to set part of their site aside for surface water management, to contribute to flood risk management in the wider area and supplement green infrastructure networks.
Z Developers should be required to maximise permeable surfaces.
Z The Councils to consider the potential for surface water management when undertaking highways schemes such as re-grading roads, to manage excess surface water runoff in the road or channel it away from high risk areas.
Z Developers should be required to utilise open green spaces as a means of managing surface water.
Z Encourage innovation in managing surface water (e.g. green roofs and permeable paving to be retro- fitted wherever possible, with sites using surface water as a resource rather than disposing of it).
Z Home owners should be encouraged to reduce impermeable surfaces and implement resilience and resistance measures. AECOM Surface Water Management Plan 45
Capabilities on project: Water
5.2 Actions An Action Plan has been developed and it is recommended that Partners agree to the Action Plan and the Councils discuss it with Members to manage surface water flooding, inform emergency planning, control drainage, review LDF land allocations, and develop investment programmes. At the same time it will contribute to the evidence base and satisfy requirements of the Flood and Water Management Act. The SWMP is a ‘living’ document and it is vital the Partners continue to work together after the completion of the SWMP. The Partners should review the SWMP on a regular basis, but there are circumstances that might trigger a review and/or an update sooner. These may include the occurrence of a flood incident or additional data becoming available, which may alter the understanding of risk within the study area or the outcome of investment decisions by Partners, which may require a revision to the Action Plan. Appendix A – Gateshead Hotspots Priority Matrix )%IGV`Z,`Q]V` 1V -`1 1H:CZJ``: `%H %`V .JQ1JZJH1RVJ 1V0VCQ]IVJ Z%1 V .V` V1$. 1J$ Q ]Q V1$. 1J$ V1$. 1J$ VJ 1:CJ``: `%H %`V V1$. 1J$ V1$. 1J$ %HQ`V &:J@ 3%-Q%J &:1C3%-Q%J &Q:R3%-Q%J 3%-Q%J 3%4Q :C-Q%J 1$.C7%CJV`:GCVJ``: `%H %`V 8 Q`V%CJV`:GCVJ``: `%H %`V 8 8 8 8 8 H.QQC^]:` 1:C_ 8 8 8 8 8 8 8 8 8 8 8 8 VCVH `1H1 7 %G : 1QJ 8 8 8 8 8 8 : 1QJ 8 8 8 8 H.QQC 8 8 H.QQC^]:` 1:C_ 8 8 8 8 8 8 H.QQC^]:` 1:C_ 8 8 VCVH `1H1 7 %G : 1QJ 8 8 8 8 8 8 8 8 ]QC1HV : 1QJ 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 H.QQC^]:` 1:C_ 8 8 8 8 8 8 8 `:1C1:7 : 1QJ 8 `:1C1:7 : 1QJ 8 8 8 8 8 8 8 8 8 8 H.QQC^]:` 1:C_ 8 8 8 8 8 8 8 8 :IG%C:JHV : 1QJ 8 8 8 Appendix B– Newcastle Hotspots Priority Matrix )%IGV`Z,`Q]V` 1V -`1 1H:CZJ``: `%H %`V .JQ1JZJH1RVJ 1V0VCQ]IVJ Z%1 V .V` V1$. 1J$ Q ]Q V1$. 1J$&Q:R3% V1$. 1J$ VJ 1:CJ``: `%H %`V V1$. 1J$3%4Q :C V1$. 1J$ %HQ`V &:J@ 3%-Q%J &:1C3%-Q%J 3%-Q%J -Q%J 1$.C7%CJV`:GCVJ``: `%H %`V -Q%J 8 Q`V%CJV`:GCVJ``: `%H %`V " 8 " " 8 " " " 8 " 8 " 8 " 8 " 8 " 8 : 1QJ 5 H.QQC " " " 8 " 8 %J10V` 1 75 : 1QJ51J`1`I:`7 " 8 : 1QJ " " 8 " 8 .Q ]1 :C " 8 " 8 " 8 " 8 " 8 " " 8 H.QQC " 8 " 8 " 8 " " 8 " 8 " " 8 " 8 H.QQC " 8 " 8 Appendix C – Gateshead Hotspot Data Sheets AECOM Surface Water Management Plan 51
Capabilities on project: Water
Hotspot Ref: GH04 Hotspot Location: Clara Vale
Hotspot Description Hotspot GH04 is in the north west of Gateshead and lies in close proximity to the River Tyne. The hotspot covers the village of Crawcrook to the south and is predominantly rural to the north covering Clara Vale. It comprises one housing site to the west of Kepier Chare, a railway line to the north and the B6317 (Main Street) running through the hotspot. Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works in the area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk. Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic Housing Land resulting from planned growth and identify Availability Drainage Areas with the greatest increase in Assessments (up to demand resulting from new development. 2020) and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify Drainage Areas with the greatest number of interactions.
Table 2 shows that GH04 lies within the Crawcrook Drainage Area and is overall ranked 54th out of the 58 Drainage Areas considered in Tyneside as part of the Tyneside Sustainable Sewerage Study. Table 2: Drainage Area Sewerage Rankings* Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) Local DA Location Growth Authority Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon)
Gateshead 05-D02 Crawcrook 46 43 36 45 170 54 MBC
* Based on data provided 19th November 2010
The capacity map analysis has deemed Crawcrook Drainage Area a low priority, with a ranking of 46 and therefore is AECOM Surface Water Management Plan 52
Capabilities on project: Water
predicted not to have network capacity issues. The bucket model analysis categorises Crawcrook Drainage Area as a low priority area with a ranking of 43 and is therefore predicted to be able to cope with volumes of a 20 year rainfall event. The growth data analysis for Crawcrook Drainage Area has been ranked at 36th which infers that other areas of Tyneside have a greater increase in demand resulting from new development and is therefore a low priority. The influence of rivers analysis for Crawcrook Drainage Area has a ranking of 45 and therefore is predicted to have a low number of interactions compared to other Drainage Areas and deemed a low priority. Gateshead Council Records of Flooding Two known incidents have been recorded on the 6-7/11/2000 and the 6- 7/09/2008 along South View, in Clara Vale and have been attributed to surface runoff from the fields immediately to the south. The risk of flooding has been categorised as ‘Low’. On both occasions South View flooded, Gateshead Council has pumped the surface water out to alleviate the flooding. South View does not have any highway drainage in light of it not having been adopted and consequently the water cannot drain into road gullies since they do not exist. As a result of climate change, it is likely that runoff from the adjacent fields will become more frequent and possibly more severe. Consequently the frequency and severity of flooding could also increase unless measures are taken to manage the surface water flows. A feasibility study6 has been undertaken which documents that South View has a history of, and is prone to regular surface water flooding, following moderate to heavy rainfall, which runs off the lane, fields and recreation area opposite. South View Four flood relief options were investigated as part of the feasibility study: - Option A - Lay a conventional highway drainage system with gullies in the un-adopted lane and a length of oversized pipe-work to act as on-line storage. The drain will be connected to the existing drainage system in Stannerford Road. - Option B - As per Option A, but with additional on-line storage and a more direct connection to the existing drainage system. - Option C – Provide a length of kerb line along the east end of the lane on the north side, to prevent surface water running down into the gardens and a kerb drainage system along the remainder to collect the surface water and act as a check to prevent water from spilling into the gardens, garages and houses. Upsized pipe-work will be provided to attenuate the flow as in Options A and B. - Option D - As Option C, but with additional storage capacity being provided by larger diameter pipework and a swale located in the adjacent play area, which is a natural low point, to provide additional storage volume. The preferred option was C which required approximately £60,000 to implement. Gateshead Council is also aware of surface water issues along Stannerford Road, notably standing water to the east of the football ground. The cause of the issue has been inadequate drainage in the combined sewer resulting in flooding to nearby properties. There have been no recorded surface water flood incidents in Crawcrook. Surface Water Flood Risk Whilst there have been no recorded problems in Crawcrook, the Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding suggest that there is a surface water risk. The modelled extents show a flow path running from Bracken Way and Cloverhill Drive, through Crawcrook and down Stannerford Road to the railway line. Approximately 580 properties fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. The source of surface water in this area is primarily runoff from the impermeable surfaces throughout Crawcook and the open fields between Crawcook and Clara Vale. The main flow path seems to follow topographic low points along Stannerford Road which links Crawcrook to Clara Vale. One school and the B6317 (Main Street) are critical infrastructure potentially at risk from surface water flooding. Areas where the depth of flooding is greater than 0.3m include; the railway line, properties to the east of the football club on Stannerford Road, and along the flow path that runs through Crawcrook affecting Garden House Estate, Chester Gardens, Allen Terrace, Kepier Chare and Cloverhill Drive.
6 South View, Clara Vale Feasibility Study, March 2010, Dodd Associates AECOM Surface Water Management Plan 53
Capabilities on project: Water
There is one housing site in Crawcook that if developed could present opportunities to manage the flood risk. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 54
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility?
Possibility for housing site. Retro-fitting of Green Roofs Yes existing buildings has limited potential. Too close to the River Tyne, high water table Soakaways/Infiltration likely. Would require geotechnical No investigation Possibility for housing site. Opportunities for storage exist near Moss Crescent, south of Attenuation/Storage the playing fields along Stannerford Yes Crescent, fields to the south of South View and to the south of the railway line. Often used alongside roads, potential Source opportunities exist along Stannerford Road, Swales/Filter Drain Yes Chester Gardens and around Kepier Chare. Further investigation required. Possible for housing site. Limited potential Permeable Paving for retro-fitting at Crawcrook. Further Yes investigation required. Boundary Flow Interception N/A No Possibility for housing site. Retro-fitting of Rainwater Harvesting Yes existing buildings has limited potential. Sewer capacity a known problem along Increase Sewer Capacity Stannerford Road. Open areas suggest Yes additional storage could be provided. Combined sewer system along North Separation of foul/surface water Crawcrook and Clara Vale which may have Yes systems opportunities to be separated including the housing site. Maintenance of drainage assets is critical to Improve maintenance regime Yes reduce the surface water risk. Opportunities for storage along Lambton Close, Kepier Chase, Main Street, Garden Flow/Storage on Roadway Yes House Estate, Stannerford Road, North View
Pathway Pathway and South View. Flows could be directed to the River Tyne or Manage overland flows Yes storage areas if they were implemented. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Limited sewer network. Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Gateshead or even nationally). Possibility as part of future development, housing site within hotspot. However, Planning policies/development planning policies and development control Yes control should be taken forward at a Council wide level for action, as opposed to at individual Receptor Receptor hotspot level. Possibility for housing site. Retro-fitting also Improve Resilience and Resistance possible and could be targeted at high risk Yes properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 55
Capabilities on project: Water
Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 1 1 1 1 1 85 Yes
Soakaways/Infiltration NA NA
Attenuation/Storage 2 1 1 2 1 1 1 135 Yes
Swales/Filter Drain 1 0 0 2 1 2 1 70 Maybe Source Source Permeable Paving 2 1 0 0 -1 1 1 80 Yes
Boundary Flow Interception NA NA
Rainwater Harvesting 2 0 1 1 1 2 1 90 Yes
Increase Sewer Capacity 1 -2 0 0 -1 1 -1 -55 No Separation of foul\surface 1 0 0 1 -2 1 1 35 water systems Maybe Improve maintenance regime 2 2 1 1 0 0 1 145 Yes Flow/Storage on Roadway 2 1 0 1 1 1 1 105 Yes
Manage overland flows 1 1 1 1 -1 1 1 90 Yes Pathway Improve channel capacity NA NA
Open up culverts NA NA Improve Floodplain Storage NA NA Remove Obstructions -1 1 1 1 0 1 1 55 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / development control 1 1 1 0 0 1 1 80 Yes
Receptor Receptor Improve Resilience and resistance 1 2 -1 0 -1 1 1 80 Yes
Development Site Gateshead Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development site presents opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where combined sewers exist, development ought to remove surface water from the combined system. Alternatively Gateshead Council may wish to consider not developing the site but promoting it as a green space into which excess flood waters could flow during extreme events that would otherwise affect the properties and B6317 in the immediate vicinity. Crawcrook Elsewhere within Crawcrook water could be contained within roads, through the provision of kerbing and re-grading roads, until the sewer system has capacity to drain the excess water. Incorporated into future capital renewal surfacing works, this would involve roadway re-grading and profiling of the carriageway profile. Retro-fitting of permeable pavements may also AECOM Surface Water Management Plan 56
Capabilities on project: Water
provide some benefit. The open land situated around Moss Crescent and to the south of Bracken Way could be used to provide upstream storage to limit water running off the fields and affecting properties. This could be in the form of a wetland to promote biodiversity or simply lower the level of the area to retain its current function. There is the potential for utilising the sand and gravel pits as a means of managing surface water. If the pits are likely to be exhausted in the near future they could be re-instated as wetlands given their proximity to green infrastructure (River Tyne) and formal overland flow paths created to channel excess flows from Crawcrook into the dis-used pits. Otherwise in the developed area of Crawcrook there are limited opportunities to implement measures other than retro-fit options such as local storage in roads or improved resilience and resistance of individual properties. Stannerford Road Standing water affects the properties to the east of the playing fields along Stannerford Road. The cause of the issue is inadequate drainage during extreme rainfall events resulting in flooding of nearby properties. Therefore maintenance is a vital aspect of managing this risk. The green space to surrounding Stannerford Road could be landscaped so as to be able to provide a swale or overland flow path and storage area during extreme events to limit water affecting properties and downstream risk areas. Local storage along Stannerford Road offers the opportunity to manage and direct the overland flows to a nearby storage area. This would alleviate the surface water risk downstream in Clara Vale. South View, Clara Vale South View is a known problem area with two recorded surface water incidents. The fields to the south and east of South View become saturated and subsequent rain runs off flooding gardens and garages. South View is a private road which does not have any highway drainage and consequently the water has nowhere to go. One option would be to carry out the works suggested in the feasibility study to conduct drainage improvements in the area at an estimated cost of £60,000. Alternatively the fields to the south and east of South View could be used to create a storage area. This could be in the form of a pond or wetland to promote biodiversity in an area that has been classified as strategic green infrastructure. Either side of Clara Vale are Clara Vale Pond, a Local Wildlife Site, and Clara Vale Pit Yard, a Local Nature Reserve. It has been suggested that diverting runoff towards the Pond, possibly using a series of swales, would help secure the water supply to the area. The presence of the railway line is likely to prevent runoff being routed further north where there are several pit ponds which can dry up having an effect upon the amphibian population. Diverting runoff towards the Pit Yard would require greater intervention in the local drainage routes. Otherwise there are opportunities to implement options such as local storage in roads or improved resilience and resistance of individual properties. The railway line runs to the north of Clara Vale and is predicted to be at risk of surface water flooding. Initially a review would be required to determine if the railway is actually at risk, lengths of the line are raised on embankments therefore it may be above the level of the water, and it has not previously been affected during the incidents when South View was flooded. If the railway is at risk of flooding, storage could be created upstream, possible as part of works for South View to prevent runoff reaching the railway. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific. AECOM Surface Water Management Plan 57
Capabilities on project: Water
Recommendations GH04.1 – Gateshead Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. GH04.2 – If the SHLAA site near Kepier Chare does not get developed, the site should be promoted as multifunctional green space into which excess runoff could flow during extreme rainfall events. GH04.3 – As part of highways maintenance programme, explore potential for storing water in roads particularly; Lambton Close, Kepier Chase, Main Street, Cloverhill Driver, South View and Garden House Estate. GH04.4 – Investigate the potential of sand and gravel pits to manage surface water. They could be re-instated as wetlands contributing to biodiversity and strategic green infrastructure. AECOM Surface Water Management Plan 58
Capabilities on project: Water AECOM Surface Water Management Plan 59
Capabilities on project: Water
Hotspot Ref: GH06 Hotspot Location: Ryton
Hotspot Description GH06 is situated in Ryton and contains a railway line and sewage treatment works to the north and the B6317, B6315 and A695. No development sites exist within the hotspot but capital works are being undertaken along Grange Drive. The hotspot is predominantly urban and lies in close proximity to the River Tyne. A green infrastructure opportunity has been identified to the north of Peth Lane. Northumbrian Water Capital Works Table 1 shows NWL are undertaking capital works along Grange Drive in Ryton. A Feasibility Study is currently underway to determine any opportunities or constraints for the potential works and the associated cost if the works were implemented. No further information is available. Table 1: Capital Works being undertaken Scheme Cause Feasibility Notes Grange Drive, Completed In progress Ryton
Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 2 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 2: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is to connectivity. provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, connectivity The purpose of NWL Buckets Model analysis is to and surface types. provide a general understanding of the ability of a DA to cope with rainfall events and identify DAs with the greatest hydraulic risk. Local Authorities Growth data in the form of The purpose of Local Authorities Growth Data analysis is Local Development to provide a general understanding of future demands of Framework Core the public sewerage system resulting from planned Strategies, Strategic Housing Land Availability growth and identify DAs with the greatest increase in Assessments (up to 2020) demand resulting from new development. and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a general watercourses and flood understanding of the interaction between high risk fluvial risk mapping flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
Table 3 shows that GH06 lies within the Ryton West Drainage Area and is overall ranked 55th out of the 58 Drainage Areas considered in Tyneside as part of the Tyneside Sustainable Sewerage Study. AECOM Surface Water Management Plan 60
Capabilities on project: Water
Table 3: Drainage Area Sewerage Rankings* Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) DA Location Local Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Ryton 05-D03 Gateshead MBC 52 44 40 37 173 55 West * Based on data provided 19th November 2010
The capacity map analysis has deemed Ryton West Drainage Area a low priority, with a ranking of 52 and therefore is predicted not to have network capacity issues. The bucket model analysis categorises Ryton West Drainage Area as a low priority area with a ranking of 44 and is therefore predicted to be able to cope with volumes of a 20 year rainfall event. The growth data analysis for Ryton West Drainage Area has been ranked at 40th which infers that other areas of Tyneside have a greater increase in demand resulting from new development and is therefore a low priority. The influence of rivers has a ranking of 37 and therefore is predicted to have a low number of interactions compared to other Drainage Areas and is a low priority. Gateshead Council Records of Flooding Three flood incidents have been recorded in GH06, two along Burnaby Drive on the 6-7/11/2000 and 6-7/09/2008. A separate incident occurred along Woodside Lane (B6315) on the 6-7/09/2008. The cause for the surface water flooding in both areas can be attributed to extreme rainfall exceeding the capacity of the sewer system. The risk of flooding in Woodside Lane is unknown but the risk has been categorised as ‘High’ along Burnaby Drive. There have been instances of standing water in and around the cricket ground which was the result of inadequate capacity in the sewer system. The cricket ground is a topographic low spot and Northumbrian Water has installed large storage tanks underneath the cricket ground to provide additional capacity in the sewer system. Surface Water Flood Risk The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding correlate well with the known incidents with a deep area of flooding located around the cricket ground and Woodside Close. The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding show a flow path, containing deep pockets of flooding, that runs from the cricket ground in an easterly direction through Greenfields, Woodside Close and along Woodside Lane. The flow path then splits into two directions, one flow path along Whitewell Lane and the other flow path to near Hexham Old Road. Approximately 510 properties fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. The source of surface water in this area is primarily from the impermeable surfaces throughout the urbanised area and runoff from the fields to the south of Ryton. There is a watercourse near Holburn Lane which is shown to have a minimal surface water risk. The watercourse receives flows from the surface water sewer network, which may have been an open watercourse at one time and has since been built over. There are three separate topographic low points at risk from ‘deep’ surface water flooding, located along Grange Drive, Greenfields and Meadow Close/Holburn Way. The Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding also show backing up behind the A695. The A695, B6315, B6317 are critical infrastructure which would benefit from surface water measures to mitigate the risk. There are no known development sites within GH06 which could have been used to manage the risk. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 4. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 61
Capabilities on project: Water
Table 4: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? No development sites. Limited potential for Green Roofs Limited retro-fitting existing buildings. Too close to the River Tyne, which will lead Soakaways/Infiltration No to a high water table. Opportunities for storage south of the cricket Attenuation/Storage ground, Grange Drive, Meadow Yes Close/Holburn Way and the A695. Often used alongside roads, potential Source Source Swales/Filter Drain opportunities south of the cricket ground and Yes along Meadow Close/Holburn Way. Retro-fitting a possibility but limited Permeable Paving Limited opportunities. No major external flow paths that influence Boundary Flow Interception No hotspot Rainwater Harvesting Limited potential to retro-fit existing buildings. Limited
Increase Sewer Capacity Space available to add storage. Yes
Separation of foul/surface water Limited, no development proposed. Limited systems Drainage exists and maintenance is critical to Improve maintenance regime reduce the surface water risk. Yes Opportunities along Greenfields, Woodside Flow/Storage on Roadway Yes Pathway Close, Woodside Lane and Whitewell Lane. Flow should be directed to the River Tyne or Manage overland flows Yes potential storage areas. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove obstructions/blockages in the sewer Remove Obstructions Yes network possible but of minimal benefit. Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Gateshead or even nationally). No development sites within hotspot. However, planning policies and development Planning policies/development control should be taken forward at a Council Yes control wide level for action, as opposed to at
Receptor Receptor individual hotspot level. No development sites. Retro-fitting also Improve Resilience and resistance possibility and could be targeted at high risk Yes properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 5. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 62
Capabilities on project: Water
Table 5: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs -1 -1 -1 2 1 2 1 -20 No
Soakaways/Infiltration NA NA
Attenuation/Storage 2 1 1 2 1 1 1 135 Yes
Swales/Filter Drain 1 0 0 2 1 2 1 70 Maybe Source Source Permeable Paving -1 -1 -1 0 -1 1 1 -65 No
Boundary Flow Interception NA NA
Rainwater Harvesting -1 -1 1 1 1 2 1 -5 No
Increase Sewer Capacity -2 -2 -2 0 -1 1 -1 -145 No Separation of foul/surface -2 -2 1 1 -2 1 -1 water systems -90 No Improve maintenance 2 2 1 1 0 0 1 145 Yes regime Flow/Storage on Roadway 2 1 1 1 1 1 1 120 Yes
Manage overland flows 2 2 1 1 -1 1 1 145 Yes
Pathway Improve channel capacity NA NA
Open up culverts NA NA Improve Floodplain Storage NA NA Remove Obstructions -1 1 1 1 0 1 1 55 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / development control 1 1 0 1 0 1 1 80 Yes
Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Main Flow Path - cricket ground to the B6315 incorporating the additional flow paths from Whitewell Lane and Hexham Old Road The deepest areas at risk along the flow path are located at the cricket ground, Greenfields, Woodside Close, Woodside Lane and the buildings to the east of Hexham Old Road. One option would be to utilise the cricket pitch as a storage area in times of extreme events, however this would impact its social function as a recreation area. An alternative is to manage surface runoff to the south of the cricket ground before it gets to Ryton in the region of the dismantled railway. The railway embankment appears to provide a restriction to flow therefore it may be straight forward to formalise this. There is the opportunity to provide storage in the road along Greenfields, Woodside Close and Woodside Lane. Incorporated into future capital renewal surfacing works, this would involve roadway re-grading and profiling of the carriageway profile to store water in the road. Improved resilience and resistance of individual properties also presents a means of managing the risk of flooding. AECOM Surface Water Management Plan 63
Capabilities on project: Water
Ryton Willows is a Site of Special Scientific Importance located to the north of the railway line away from the urban area of Ryton. It was identified that the creation of further ponds in this area would be beneficial. Re-grading Whitewell Lane as part of resurfacing works to guide overland flows down towards this area may help to facilitate the creation of additional ponds to support the SSSI. Grange Drive Grange Drive is located in a topographic low point and is at risk from deep surface water flooding caused by heavy rain running off the fields to the south. A storage area immediately to the south could be used to alleviate the flood risk at Grange Drive. This could be in the form of a pond or wetland to promote biodiversity. There is an opportunity to provide storage in the roads which could be used to convey water to the storage area or hold the water in situ. Source control measures are unlikely to be cost effective as they will need to be retro-fitted. A695 The A695 is critical infrastructure at risk of surface water flooding. The source of the risk is runoff from the fields to the south. There is an opportunity to use the surrounding rural land to the south as a storage area in the form of a wetland or pond to alleviate the risk and promote biodiversity in the area. This option could involve providing storage alongside the A695 or landscaping the land to the south of the motorway so as to divert and manage the overland runoff away from the A695. Meadow Close/Holburn Way Similar to Grange Drive, Meadow Close and Holburn Way are situated in a topographic low point with the roads and impermeable surfaces conveying the surface water. There may be an opportunity to use the roads to help manage the overland flow so that it enters the undesignated watercourse to the west. Swales and filter drains or storage in roads could be used to manage the risk. Where possible, owners in these areas should be encouraged to reduce impermeable surfaces and implement resilience measures. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations GH06.1 – As part of highways maintenance programme, explore potential for storing water in roads particularly; Greenfields, Woodside Close, Woodside Lane, Meadow Close and Holburn Way. GH06.2 – Assess suitability of using open green space as storage areas during extreme events. Potential locations include land near Moss Crescent, Bracken Way, Stannerford Road and South View. AECOM Surface Water Management Plan 64
Capabilities on project: Water AECOM Surface Water Management Plan 65
Capabilities on project: Water
Hotspot Ref: GH14 Hotspot Location: Blaydon
Hotspot Description GH14 is situated in the industrial area of Blaydon to the south of Blaydon Haughs. The hotspot is intersected by the A1, Blaydon Highway/Chainbridge Road (A695), the B6317 and a railway line and station which have all been identified as critical infrastructure. No development sites exist within the boundary although the hotspot shares its western boundary with Blaydon Town Centre Strategic Site and its south-west boundary with hotspot GH15. GH14 falls within a strategic green infrastructure opportunity area and an area of strategic green infrastructure. The Strategic Flood Risk Assessment has identified functional floodplain on Blaydon Dene which is to the west of Blaydon Town Centre Strategic Site and that development in the area ought to endeavour to restore the watercourses. Northumbrian Water Capital Works NWL are not undertaking any capital works in the area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is to connectivity. provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, connectivity The purpose of NWL Buckets Model analysis is to and surface types. provide a general understanding of the ability of a DA to cope with rainfall events and identify DAs with the greatest hydraulic risk. Local Authorities Growth data in the form of The purpose of Local Authorities Growth Data analysis is Local Development to provide a general understanding of future demands of Framework Core the public sewerage system resulting from planned Strategies, Strategic Housing Land Availability growth and identify DAs with the greatest increase in Assessments (up to 2020) demand resulting from new development. and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a general watercourses and flood understanding of the interaction between high risk fluvial risk mapping flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
Table 2 shows that GH14 falls within the Blaydon Haughs and Blaydon East Drainage Areas. Overall, Blaydon Haugh Drainage Area is ranked 17th and Blaydon East is ranked 52nd out of 58 considered in Tyneside as part of the Tyneside Sustainable Sewerage Study. It should be noted that the relative rankings for Blaydon Haugh Drainage Area is 1st for the ‘Bucket Model‘ which infers that the drainage area is unable to cope with volumes of a 20 year rainfall event. Blaydon Haugh Drainage Area is also ranked 8th for the ‘Influence of Rivers’ which infers that there are a high number of interactions between high risk fluvial flooding locations and discharges from the public sewerage system when compared to other drainage areas in Tyneside. AECOM Surface Water Management Plan 66
Capabilities on project: Water
Table 2: Drainage Area Sewerage Rankings* Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) Local DA Location Growth Authority Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon)
Blaydon Gateshead 05-D08 48 1 40 8 97 17 Haughs MBC
Blaydon Gateshead 05-D07 43 29 40 49 161 52 East MBC
* Based on data provided 19th November 2010
Gateshead Council Records of Flooding Based on the information provided by Gateshead Council, three recorded flood incidents have been recorded on the 29/03/1979, 6-7/11/2000 and the 6-7/09/2008, located close to the River Tyne along Derwentwater Road. The cause is attributed to fluvial flooding of the River Tyne. The risk of flooding has been categorised as ‘Low’. The land to the south west of the hotspot at Shibdon Dene is very steep, sloping towards the hotspot, which then flattens out to the east of Shibdon Road (B6317). GH14 covers the flat plateau of land which is made up of impermeable surfaces that will exacerbate the surface water risk, e.g. car parks for the shopping centres and industrial units. Furthermore there is a dense network of combined sewers, which have the potential to back up due to the loss in gradient due to the local topography. Surface Water Flood Risk The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding correlate well with each other and the known areas at risk. Areas of deep flooding (>0.3m) are located to the north of Shibdon Dene affecting commercial units, the A695, B6317 and the railway line which can be attributed to the steep topography conveying surface water to the flat area to the east of Shibdon Road (B6317). The risk is exacerbated by the presence of impermeable surfaces. The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding show extensive flooding between the railway and the A695. The A695 and the railway act as a barrier to intercept flow which would otherwise feed into the River Tyne. As a result the surface water cannot easily escape resulting in flooding of industrial units and the A1. Whilst the Areas Susceptible to Surface Water Flooding show the A1 to be at risk of flooding it is actually elevated some distance above the ground at this location and would not be affected. Approximately 96 properties fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. The railway line, A695 and B6315 are critical infrastructure which would benefit from surface water measures to mitigate the surface water risk. An undesignated watercourse exists to the south-west of GH14 in Shibdon Dene that becomes culverted upon entry into the hotspot. There is a risk of backing up behind the culvert in times of extreme flows caused through blockages or potentially inadequate capacity. Due to the topographical nature of Shibdon Dene the flows would flow into the hotspot flooding Shibdon Business Park. A flow path exists down Blaydon Bank. The Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding suggest the overland flows get onto Tyne Street, contributing to the surface water risk to the /industrial units and the critical infrastructure on the western side of the hotspot. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 67
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? No development sites. Limited potential for retro-fitting existing buildings at Shibdon Limited Green Roofs Business Park, Blaydon Industrial Estate and the works to the north of the railway. Too close to the River Tyne and Derwent, Soakaways/Infiltration high water table likely requires geotechnical No investigation. Opportunities for storage to the south of Shibdon Green, parkland to the east of Yes Attenuation/Storage Evelyn Terrace and parkland to the east of Shibdon Business Park.
Source Source Often used alongside roads, and there are potential opportunities for installation along Swales/Filter Drain the A695, B6317, Blaydon Bank, rural Yes pathway running through Shibdon Dene and Chainbridge Road. Retro-fitting a possibility at Shibdon Business Permeable Paving Park, Blaydon Industrial Estate and the Yes works north of the railway. External flows from the west along Tyne Yes Boundary Flow Interception Road and from Shibdon Dene No development sites. Retro-fitting of Yes Rainwater Harvesting existing buildings is an option. Sewer capacity not a known problem in the Limited Increase Sewer Capacity area. Limited information available. Combined sewer system to the west of Separation of foul/surface water Blaydon Industrial Park along Tyne Street Limited systems which has the opportunity to be separated. Limited opportunities elsewhere. Drainage exists and maintenance is critical to Yes Improve maintenance regime reduce the surface water risk.
Opportunities for storage along A695, B6317, Flow/Storage on Roadway Blaydon Bank, rural pathway running through Yes Pathway Shibdon Dene and Chainbridge Road. Flow should be directed to the River Tyne or Yes Manage overland flows potential storage areas. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove obstructions/blockages in the sewer Remove Obstructions network and culverted sections of the Limited undesignated watercourses Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Gateshead or even nationally). No development sites within hotspot. However, planning policies and development Planning policies/development control should be taken forward at a Council Limited control wide level for action, as opposed to at
Receptor Receptor individual hotspot level. No development sites. Retro-fitting also Improve Resilience and resistance possibility and could be targeted at high risk Yes properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 68
Capabilities on project: Water
Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 1 0 1 1 -1 2 1 60 Maybe
Soakaways/Infiltration NA
Attenuation/Storage 1 1 1 2 0 1 1 110 Yes
Swales/Filter Drain 1 1 0 1 0 1 1 80 Yes Source Source Permeable Paving 2 1 0 0 -1 1 1 80 Yes
Boundary Flow Interception 2 1 1 0 -1 1 1 95 Yes
Rainwater Harvesting 1 0 1 1 1 2 1 70 Maybe
Increase Sewer Capacity -2 -2 -1 0 -2 -1 -2 -150 No Separation of foul/surface 2 0 1 1 -1 1 1 75 Maybe water systems Improve maintenance 1 1 0 0 0 0 1 60 Maybe regime Flow/Storage on Roadway 2 1 -1 0 1 1 1 75 Maybe
Manage overland flows 2 2 0 0 -1 1 1 115 Yes
Pathway Improve channel capacity NA
Open up culverts NA Improve Floodplain NA Storage Remove Obstructions 1 1 0 0 0 0 1 60 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / 2 2 0 0 0 1 1 120 Yes development control
Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Blaydon Town Centre Strategic Site The Blaydon Town Centre Strategic Site is addressed in the Strategic Development Sites report that has been produced as part of the NewcastleGateshead SWMP. The options recommended for the Strategic Development Site are: - Investigate the opportunity for a large storage area along the River Tyne for the times when this site is tide locked and surface water cannot drain. - Investigate the storage and pipe size for discharge of surface water to the River Tyne. - Assess the potential for a defined flow path through the site into the sewers and connected to the River Tyne - Assess the benefit of developing in the south-east of the site - Investigate potential to store water within roadways and car parks located near sewer networks - Encourage source control measures such as green roofs, swales, permeable paving, rainwater harvesting and attenuation basins. AECOM Surface Water Management Plan 69
Capabilities on project: Water
- Implement resilience and resistance measures. Development of the Strategic Site presents the opportunity to undertake capital works on the sewer network and provide additional storage. The lack of development in the neighbouring hotspot GH14 means that any works associated with the sewer network would have to be retro-fitted which would make them very expensive and unlikely to be cost beneficial. If development of the Strategic Site is able to provide storage along the Tyne or a flow path to allow surface water to get into the sewers and ultimately into the River Tyne, the proposals should endeavour to address the risk associated with the Blaydon Highway (A695) which is immediately to the north. Blaydon Industrial Park, A695 and B6317 Blaydon Industrial Park lies south of the A695, north of the B6317 (Shibdon Road) and to the east of the Blaydon Town Strategic Site. Blaydon Industrial Park, the A695 and B6317, would benefit from the provision of a storage area prescribed for the Strategic Site. The storage area can be sited upstream of Shibdon Dene in the amenity grassland north of Widdington Road. The storage area can be used to mitigate the surface water running down the steep slopes, through Shibdon Dene to the hotspot. The land may require lowering in order to act as a storage area and would impact its current social function. Alternatively the storage could be provided within the Strategic Site. The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding show three flow paths running from amenity grassland towards the hotspot that will need to be managed. The flow path to the east follows a rural pathway that can use swales and filter drains to store the water in times of extreme rainfall. There is an opportunity for additional storage in parkland to the east of Evelyn Terrace. The remaining two flow paths run through Shibdon Dene. One solution would be to use Blaydon Bank as an overland flow path to channel runoff to a storage area or the River Tyne. Additional storage is available in the football pitches to the west of Chesmond Drive which may need lowering in order to act as a storage area and retain its current social function. There is the opportunity to alleviate the surface water risk by placing a culvert under the active railway line and A695 along with an overland flow path such as a swale to allow the surface water to discharge into the River Tyne. Alternatively the flat roofs at Blaydon may present opportunities to retro-fit green roofs. Permeable pavements may also provide some benefit if retro-fitted. The Environment Agency is concerned that the sewer network may back up during extreme events and spill out on to Blaydon Industrial Park and nearby properties. No known drainage incidents have occurred which infers the sewer network can cope with increased capacity from a storm event. As a result the risk has been deemed low and options such as increasing sewer capacity and separating foul and surface flows are not economically viable. If drainage incidents occur in the future, it may be necessary to revise this area with the possibility of separating the foul and surface systems in order to reduce the risk. Works between the A695 and the railway line The area is constrained by the A695 and the railway line. As the area is a constrained and a topographic low the most practical option is to manage the surface water in situ. Source control measures such as the retro-fitting of green roofs, rainwater harvesting or permeable paving will provide some benefit to controlling the surface water risk. There are limited opportunities to implement measures other than retro-fit options such as local storage in roads or improved resilience and resistance of individual properties. Incorporated into future capital renewal surfacing works, this would involve roadway re- grading and profiling of the carriageway profile to provide overland flow paths out of the area, into a storage area such as the parkland to the east of Shibdon Business Park or into the River Tyne. Retro-fitting of permeable pavements may provide some benefit. There is an ELR site to the south of the site in neighbouring hotspot GH15 which could be used to reduce the surface water risk. For example the ELR could be used as a storage area, however there needs to be a flow route under the railway that separates the two hotspots to manage the surface water. Please refer to GH15 for more information on the site and the potential options. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific. AECOM Surface Water Management Plan 70
Capabilities on project: Water
Recommendations GH14.1 – As part of highways maintenance programme, explore potential for storing water in roads. GH14.2 – Gateshead Council to encourage developer of Strategic Site to explore potential to provide wider benefits. AECOM Surface Water Management Plan 71
Capabilities on project: Water AECOM Surface Water Management Plan 72
Capabilities on project: Water
Hotspot Ref: GH15 Hotspot Location: Blaydon
Hotspot Description Hotspot GH15 is situated in the industrial area of Blaydon bounded to the north by the railway line and the A1 to the west. An industrial estate is present in the north-west of the hotspot and has been identified for future development (ELR site). The eastern portion of the hotspot is open land which has an undesignated watercourse flowing through it. GH15 lies within a area of strategic green infrastructure and a green infrastructure opportunity area. The hotspot shares its northern boundary with hotspot GH14. Northumbrian Water Capital Works NWL are not undertaking any capital works in the area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is to connectivity. provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, connectivity The purpose of NWL Buckets Model analysis is to and surface types. provide a general understanding of the ability of a DA to cope with rainfall events and identify DAs with the greatest hydraulic risk. Local Authorities Growth data in the form of The purpose of Local Authorities Growth Data analysis is Local Development to provide a general understanding of future demands of Framework Core the public sewerage system resulting from planned Strategies, Strategic Housing Land Availability growth and identify DAs with the greatest increase in Assessments (up to 2020) demand resulting from new development. and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a general watercourses and flood understanding of the interaction between high risk fluvial risk mapping flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
Table 2 shows that GH15 falls within the Blaydon Haughs Drainage Area. Overall, Blaydon Haugh Drainage Area is ranked 17th out of 58 considered in Tyneside as part of the Tyneside Sustainable Sewerage Study. It should be noted that the relative rankings for Blaydon Haugh Drainage Area is 1st for the ‘Bucket Model‘ which infers that the drainage area is unable to cope with volumes of a 20 year rainfall event. Blaydon Haugh Drainage Area is also ranked 8th for the ‘Influence of Rivers’ which infers that there are a high number of interactions between high risk fluvial flooding locations and discharges from the public sewerage system when compared to other drainage areas in Tyneside. The capacity map analysis has deemed Blaydon Haughs Drainage Area a low priority, with a ranking of 48 and therefore is predicted not to have network capacity issues. The growth data analysis for Blaydon Haughs Drainage Area has been ranked at 40th which infers that other areas of Tyneside have a greater increase in demand resulting from new development and is therefore a low priority. AECOM Surface Water Management Plan 73
Capabilities on project: Water
Table 2: Drainage Area Sewerage Rankings* Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) Local DA Location Growth Authority Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon)
Blaydon Gateshead 05-D08 48 1 40 8 97 17 Haughs MBC
* Based on data provided 19th November 2010
Gateshead Council Records of Flooding There are no known incidents of surface water flooding in GH15. Surface Water Flood Risk The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding show limited flooding in the hotspot. There is an undesignated watercourse that runs through Shibdon Pond Nature Reserve, under the A1 and into hotspot GH15, before eventually discharging into the River Tyne. The main area of surface water risk is the rural land alongside the undesignated watercourse. The risk is a mix of surface water flowing off the fields to the south-east and the undesignated watercourse. There may be capacity issues associated with the undesignated watercourse and the culvert at the eastern end of the hotspot, which could be exacerbated by obstructions or blockages. Shibdon Pond also exhibits areas of surface water flooding which may pass into GH15 via the undesignated watercourse. Alternatively the culvert underneath the A1 could act as a throttle holding water back in the Pond rather than affecting GH15. Any options that are put forward will need to have consideration for GH20 as well as GH15. Shibdon Pond is a Site of Special Scientific Interest, a Local Wildlife Site and a Local Nature Reserve. Approximately five properties fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 74
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility during future development, ELR Green Roofs site within hotspot and potential to retrofit flat Yes roofs that exist. Too close to the Rivers Tyne & Derwent, Soakaways/Infiltration high groundwater likely requires geotechnical No investigation. Possibility during future development, ELR site within hotspot. Opportunities for storage Yes Attenuation/Storage either side of the undesignated watercourse and within in Shibdon Pond Nature Reserve. Source Source Often used alongside roads and there are Yes Swales/Filter Drain potential opportunities. Possible during future development, ELR site Yes Permeable Paving within hotspot. Flow paths from Shibdon Pond could be Yes Boundary Flow Interception influencing the hotspot. Possibility for, ELR site. Retro-fitting of Yes Rainwater Harvesting existing buildings an option. Sewer capacity is not a known problem in the Limited Increase Sewer Capacity hotspot. Limited sewer coverage in this area. Separation of foul/surface water No combined sewers in the area. No systems Poor drainage exists along the undesignated Improve maintenance regime watercourse. Maintenance could reduce the Yes
surface water risk.
Pathway Flow/Storage on Roadway Flooding is not affecting roads. No Flow should be directed to the River Tyne or potential storage areas either side of the Yes Manage overland flows undesignated watercourse and upstream at Shibdon Pond Nature Reserve Potentially inadequate channel capacity of Yes Improve channel capacity the undesignated watercourse Potentially inadequate capacity at the A1 Yes Open up culverts culvert entrance and outfall to the hotspot Opportunities for floodplain storage along either side of the undesignated watercourse Yes Improve floodplain storage and upstream at Shibdon Pond Nature Reserve. Remove obstructions/blockages in the sewer Remove Obstructions network, culvert and the undesignated Yes watercourse Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Gateshead or even nationally). Possibility during future development, and ELR site within hotspot. However, planning Planning policies/development policies and development control should be Yes control taken forward at a Council wide level for Receptor Receptor action, as opposed to at individual hotspot level. Possibility during future development, and Yes Improve Resilience and resistance ELR site within hotspot.
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 75
Capabilities on project: Water
Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 1 1 1 0 0 1 110 Yes
Soakaways/Infiltration NA NA
Attenuation/Storage 2 0 1 2 1 1 2 105 Yes
Swales/Filter Drain 2 1 1 1 1 1 1 120 Yes Source Source Permeable Paving 2 1 0 0 -1 1 1 80 Yes
Boundary Flow Interception NA NA
Rainwater Harvesting 2 1 1 0 0 1 1 100 Yes
Increase Sewer Capacity 2 -2 0 0 -2 0 -2 20 No Separation of foul/surface NA NA water systems Improve maintenance 2 0 0 0 0 0 1 45 Maybe regime Flow/Storage on Roadway NA NA
Manage overland flows 1 -1 0 1 -1 0 1 0 No
Pathway Improve channel capacity 2 -2 0 -2 -2 2 1 -55 No
Open up culverts -1 -2 -1 2 -2 2 2 -65 No Improve Floodplain 2 -1 0 2 1 2 2 60 Maybe Storage Remove Obstructions 2 0 0 1 0 0 0 55 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / 2 1 0 0 0 0 1 80 Yes development control
Receptor Receptor Improve Resilience and 2 0 -1 0 -1 1 1 30 Maybe resistance
Development Site Gateshead Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The ELR development site presents opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Undesignated Watercourse The undesignated watercourse that flows through the hotspot presents the greatest risk of surface water flooding however given that very little is at risk undertaking works is economically unviable. Additionally part of Shibdon Meadow is located within GH15, which is classified as a Local Wildlife Site, therefore any mitigation measures such as maintenance of the watercourse could negatively impact upon the surrounding ecological environment. The watercourse that flows through GH15 originates from Shibdon Pond, a Site of Special Scientific Interest (SSSI), a Site of Nature Conservation Importance (SNCI) and a Local Nature Reserve. This pond is linked to Shibdon Meadow via a large culvert and has been highlighted as pivotal to the water level management of Shibdon Pond, as well as providing a safe AECOM Surface Water Management Plan 76
Capabilities on project: Water passage for wildlife to the River Tyne, including otters. The water levels of Shibdon Pond are managed through the use of weirs and sluices for the benefit of wildlife by maintaining a suitable living environment during the changing seasons. The raising of pond water levels offers increased protection to nesting birds from land predators, but also provides a habitat for priority species such as otters, water voles and great crested newts. Part of the watercourse’s floodplain has been designated as functional floodplain by the SFRA. There may be opportunities for the development to utilise the floodplain as a means of storing excess surface water although it could not reducing the existing storage area. Development in the functional floodplain is restricted; PPS25 states that only water compatible uses and essential infrastructure which passes the Exception Test should be permitted in this zone. Receptor Mitigation Measures Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations GH15.1 – Gateshead Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments
. AECOM Surface Water Management Plan 77
Capabilities on project: Water AECOM Surface Water Management Plan 78
Capabilities on project: Water
Hotspot Ref: GH21 Hotspot Location: Derwent Haugh
Hotspot Description GH21 is situated to the east of Blaydon, on the right bank of the River Derwent at the confluence with the River Tyne. The A1 runs through the hotspot, with the retail park in Derwent Haugh to the north, and residential, commercial and industrial areas in North Whickham and Swalwell to the south of the A1. Two development sites exist within the hotspot; one commercial and one residential. GH21 shares its western boundary with the Metro Site 3 Strategic Site. The hotspot has been identified as a green infrastructure opportunity area. Northumbrian Water Capital Works NWL are not undertaking any capital works in the area. Tyneside Sustainable Sewerage Study Assessment The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is to connectivity. provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, connectivity The purpose of NWL Buckets Model analysis is to and surface types. provide a general understanding of the ability of a DA to cope with rainfall events and identify DAs with the greatest hydraulic risk. Local Authorities Growth data in the form of The purpose of Local Authorities Growth Data analysis is Local Development to provide a general understanding of future demands of Framework Core the public sewerage system resulting from planned Strategies, Strategic Housing Land Availability growth and identify DAs with the greatest increase in Assessments (up to 2020) demand resulting from new development. and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a general watercourses and flood understanding of the interaction between high risk fluvial risk mapping flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
Table 2 above shows that GH21 lies within the Whickham North Drainage Area (DA) and is ranked 32nd overall out of the 58 Drainage Areas considered in Tyneside as part of the Tyneside Sustainable Sewerage Study. As such it is a relatively low priority area. Table 2: Drainage Area Sewerage Rankings* Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) Local DA Location Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon)
Whickham Gateshead 05-D10 21 20 34 43 118 32 North MBC
* Based on data provided 19th November 2010 AECOM Surface Water Management Plan 79
Capabilities on project: Water
The capacity map analysis has deemed Whickham North DA a moderate priority, with a ranking of 21 and therefore is predicted to have possible network capacity issues; however there are 20 sites with a higher priority status. The bucket model analysis categorises Whickham North DA as a moderate priority area with a ranking of 20, therefore there is uncertainty regarding the ability for the DA to cope with volumes of a 20 year rainfall event, however there are 19 sites with a higher priority status. The growth data analysis has been ranked at 34th which infers that other areas of Tyneside have a greater increase in demand resulting from new development and is therefore a low priority. The influence of rivers analysis has a ranking of 43 and therefore is predicted to have a low number of interactions compared to other DA areas and deemed a low priority. Gateshead Council Records of Flooding There are no known recorded surface water incidents in GH21, however Gateshead Council are aware that Blaydon Rugby Club has a history of flooding from the River Derwent. The rugby club and adjoining land has been classified as functional floodplain (Flood Zone 3b) in the Gateshead SFRA. The local topography is very steep to the south in Swalwell which then flattens off north of the A1 where the Metro Retail Park is sited. The retail park contains a large area of car parking (impermeable surfaces) that will exacerbate the surface water risk. Furthermore there are combined sewers which run in a southerly direction from Swalwell towards the A1 which have the potential to back up due to the loss in gradient. The Environment Agency believes this is a potential risk area given the low lying nature of the area and its location at the confluence of the Rivers Tyne and Derwent. High water levels in these rivers could impede the ability of any sewers to discharge. The Tyne and Derwent are both tidally influenced at this location therefore tide-locking of the surface water sewers could be a source of surface water flooding given the low land elevations. Further investigation would be required to determine if the sewers were affected by tide-locking. Surface Water Flood Risk The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding correlate well with each other and show the deepest flooding (>0.3m) in Swalwell along The Covers, The Pavilion, Industrial Estate to the south of Square Bridge, Sands Industrial Estate to the north of Sands Road that contains B&Q, the Works west of Mill Farm which includes Northumbria Cars and along Marcon Way. The surface water risk looks to cross the A1 to the north with extensive yet shallow flooding of the Metro Retail Park, in particular the car parks and impermeable areas that surround IKEA, DFS and Pets at Home. The A1 is elevated at this location and water would flow through the two underpasses beneath the A1 rather than over it. There is the possibility of a fluvial influence from the River Derwent that could be contributing to the risk south of the A1. The sewer network has a mixture of combined and separate systems, with the surface water sewers discharging into the River Derwent. However, the River Derwent is tidally influenced, therefore the surface water may not be able to discharge during high tide causing surcharging and flooding. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 80
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing and employment sites Green Roofs within hotspot. Retro-fitting of existing Yes buildings an option. Too close to the River Tyne and the River Soakaways/Infiltration Derwent, high water table would require No geotechnical investigation. Possibility on housing and employment sites within hotspot. Opportunities for storage Yes Attenuation/Storage south of Hexham Road, east of Mill Farm and south of Square Bridge Industrial Estate.
Source Source Often used alongside roads, however further Yes Swales/Filter Drain investigation would be required. Possible for housing and employment sites within hotspot. Retro-fitting a possibility for Yes Permeable Paving large areas of hard standing on industrial and retail estates. Flows should be directed towards the River Boundary Flow Interception Derwent or into storage areas that would Yes need to be created. Possibility for housing and employment site Rainwater Harvesting within hotspot. Retro-fitting of existing Yes buildings an option. Redevelopment of the employment site and Increase Sewer Capacity Strategic Site present potential to expand the Yes sewer network in the urban area. Combined sewer system in region of Separation of foul/surface water employment site which has the opportunity to Yes systems be separated. Drainage exists and maintenance is critical to Yes Improve maintenance regime reduce the surface water risk.
Opportunities for storage to the south of Flow/Storage on Roadway Hexham Road, east of Mill Farm and south Yes Pathway of Square Bridge Industrial Estate. Flow should be directed to the River Derwent Yes Manage overland flows or potential storage areas. Opportunity to increase the River Derwent's Limited Improve channel capacity channel capacity is limited. Open up culverts No culverts exist in this hotspot No Opportunity to improve floodplain storage Yes Improve floodplain storage south of Hexham Road Remove obstructions/blockages in the sewer Yes Remove Obstructions network. Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Gateshead or even nationally). Possibility during future development, housing and employment site within hotspot. Planning policies/development However, planning policies and development Yes control control should be taken forward at a Council wide level for action, as opposed to at individual hotspot level. Receptor Receptor Possibility during future development, housing and employment site within hotspot. Improve Resilience and resistance Retro-fitting also possibility and could be Yes targeted at high risk properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. AECOM Surface Water Management Plan 81
Capabilities on project: Water
Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 1 1 2 1 2 1 140 Yes
Soakaways/Infiltration NA NA
Attenuation/Storage 2 1 1 2 1 1 1 135 Yes
Swales/Filter Drain 1 0 0 2 1 2 1 70 Maybe Source Source Permeable Paving 2 1 0 0 -1 1 1 80 Yes
Boundary Flow Interception 1 1 1 0 -1 1 1 75 Maybe
Rainwater Harvesting 1 1 1 1 1 2 1 105 Yes
Increase Sewer Capacity 1 1 1 0 -1 0 -1 60 Maybe Separation of foul/surface 2 0 1 1 -2 1 1 70 Maybe water systems Improve maintenance 2 0 0 0 1 0 1 50 Maybe regime Flow/Storage on Roadway 2 1 0 1 1 1 1 105 Yes
Manage overland flows 1 1 1 1 -1 1 1 90 Yes
Pathway Improve channel capacity -1 -2 -1 -1 -1 1 -1 -125 No
Open up culverts NA NA Improve Floodplain 2 1 0 2 1 1 2 125 Yes Storage Remove Obstructions 1 0 1 0 0 0 1 40 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / 2 1 0 0 0 0 1 80 Yes development control
Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Site Gateshead Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The two development sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where combined sewers exist, development ought to remove surface water from the combined system. The Sites and the Strategic Development Site adjacent may also present opportunities to increase the sewer capacity in the area, although this would require detailed investigation. There may be restrictions on the public sewer capacity, any additional capacity would need to be accommodated by the developer. The Covers and The Pavilion The residential properties at risk appear to have both fluvial and surface water issues. The River Derwent is tidally AECOM Surface Water Management Plan 82
Capabilities on project: Water
influenced; therefore the surface water may not be able to discharge during high tides, or flood flows leading to surcharging and flooding. One option is to provide storage in the fields to the south of Hexham Road, an area designated as functional floodplain. This would act as both a floodplain and surface water storage area. The area may need to be lowered in order for it to be act as a storage area, could disrupt its current social function and would need to ensure that it did not reduce the current floodplain volume. A formal overland flow path would need to be created and managed to allow surface water to drain across Hexham Road into this area. Alternatively the risk can be managed by providing a formal overland flow path that discharges straight into the River Derwent. This could be implemented through re-grading roads or through swales and filter drains along The Covers and The Pavilion, and a means of discharging into the river. Otherwise in this developed area there are limited opportunities to implement measures other than improved resilience and resistance of individual properties. Industrial Estate to the south of Square Bridge The car parks and outer grounds look to be at risk from surface water. There is the opportunity for source control measures such as permeable paving, attenuation storage, green roofs and rainwater harvesting to be adopted in the housing sites that are situated to the south of the industrial estate. In comparison, the industrial estate itself may benefit from permeable paving and has flat roofs in which green roofs could be retro-fitted, but these measures would prove more expensive. The industrial estate is in close proximity to the recreational land to the west which could be used as a storage area to hold runoff back before it reaches the industrial estate. The area could be lowered to maintain its existing function or be used as a wetland to provide biodiversity benefits. Alternatively there is room for storage to the south of the industrial estate alongside the housing sites. Swalwell Bank looks to be conveying flows in this direction which could be managed by providing storage alongside the road and down Woodhouse Lane to a potential storage area to the south. Sands Industrial Estate Retro-fitting of green roofs and permeable paving may provide some benefit. Additionally there is the opportunity for floodplain storage in the parkland between the industrial estate and the River Derwent. If the risk is purely surface water, the risk can be managed in situ by providing a formal overland flow path that can discharge the surface water into the River Derwent. Metro Retail Park North of the A1, surface water ponds around IKEA, DFS and Pets at Home due to the extensive impermeable surfaces. Retro-fitting source control measures such as permeable paving, green roofs and swales/filter drains could reduce the impermeable surfaces and mange the surface water in situ. Metro Site 3 Strategic Site borders this area whereby the surface water ponds due to limited formal drainage. The Strategic Development Sites report produced as part of the NewcastleGateshead SWMP put forward the following measures to manage surface water: - Assess River Derwent flood levels, capacity and tidal influence, particularly tidal locking for future developments. - Investigate the opportunity for swales or filter drains at the Works to direct flows from the east into the River Derwent. - Assess the opportunity to collect flows on the site boundary from the adjacent IKEA car parking and roof area and direct into new drainage lines. - Investigate the opportunity for a storage area for new developments, notably around IKEA. This would require external surface water flows towards the River Derwent and directing surface water away from the existing combined sewers and building accesses. - Assess implementing an improved maintenance regime. - Implement resilience and resistance measures. The second bullet point recommends swales to transport runoff from the retail park across the Strategic Site and into the River Derwent. This is a result of runoff from the retail park posing a risk to the Strategic Site. Re-grading the local roads may offer opportunities to link Metro Site 3 with the Metro Retail Park and mange surface water through formal overall flow paths, such as swales, to drain excess runoff into the River Derwent. AECOM Surface Water Management Plan 83
Capabilities on project: Water
Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations GH21.1 – Gateshead Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments, where possible surface water should be removed from the combined sewer network. GH21.2 – As part of highways maintenance programme, explore potential for storing water in roads and directing it into storage areas or the River Derwent. AECOM Surface Water Management Plan 84
Capabilities on project: Water AECOM Surface Water Management Plan 85
Capabilities on project: Water
Hotspot Ref: GH26 Hotspot Location: South of Lobley Hill
Hotspot Description This rural hotspot lies on the Black Burn, a tributary of the River Team. Coxclose Dene and The Trench are ordinary watercourses that feed into Black Burn. The hotspot lies south of Lobley Hill residential estate and west of Team Valley between two roads, Gateshead Road to the west and Coach Road to the east. The watercourse itself has been buried and open space comprises the majority of the hotspot. The western tip of the hotspot has been identified as a green infrastructure opportunity area. Northumbrian Water Capital Works NWL are not undertaking any capital works in the area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area GH26 falls outside the drainage areas that have been supplied. Gateshead Council Records of Flooding No recorded surface water incidents are within this hotspot. An incident is recorded immediately downstream of GH26 within GH40. The Black Burn has been culverted and is now buried deep underneath a landfill. Another watercourse (possibly along Alwinton Gardens) has also been buried. Alwinton Gardens is a low spot and the flood incident there was water in a garage. The college to the north has significantly increased the area of impermeable surfaces which has increased runoff and led to surface water problems. Gateshead Council has undertaken work in combination with Northumbrian Water to divert water away from the area. At Coach Road the Black Burn comes out of culvert before going under the Western Bypass in another culvert. The known flood incident, located to the east of the hotspot, was a result of debris blocking the culvert under the bypass. As a consequence water flowed through the subway located next to the watercourse. Gateshead Council has recently changed the grill on the culvert so it is sloped rather than flat to alleviate the risk. Approximately 5 properties fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. The River Team Integrated Modelling Study which should provide greater insight into the interaction of ordinary watercourses and surface water flooding on the Team Valley. Surface Water Flood Risk The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding correlate well with each other, however the risk appears to be from the buried watercourse; Black Burn. There are no known incidents, development sites or sewer networks within the hotspot. Undesignated watercourses (drains) exist to the west of the site that feed into Black Burn and have the potential to exacerbate the risk in GH26. The A692 looks to convey surface water from Watergate Lodge to Beggar Wood where it ponds, potentially combining with Black Burn. Similarly Consett Road conveys water towards Black Burn at Beggar Wood. Deep flooding (>0.3m) is also located along the path to the north of Black Burn and to the east of Coach Road. Coach Road and the A1 partially act as a barrier to flow. Any surface water in this location will combine with Black Burn and exacerbate the risk at the culvert entrance to Team Valley. Whilst the A1 is shown to be at risk of flooding by the Areas Susceptible to Surface Water Flooding data it is raised up on an embankment at this loction and would not be inundated. Team Valley is a high surface water risk area where works are already being undertaken to manage the surface water risk. This hotspot potentially contributes to the risk in Team Valley. Options to manage the surface water risk take this into account so as to benefit the wider area. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 1. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 1. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 86
Capabilities on project: Water
Table 1: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Potential for SLR site. Minimal properties located within the hotspot, retro-fitting a Yes Green Roofs possibility at the properties to the south of Rowanwood Gardens. Hotspot on Black Burn. High groundwater No Soakaways/Infiltration likely requires geo-technical investigation. Potential for SLR site. Opportunities for Attenuation/Storage storage throughout the hotspot and to the Yes south of the hotspot. Potential for swales and filter drains along Source Source Swales/Filter Drain the pathway running to the north of Black Yes Burn. Potential for SLR site. Minimal properties located within the hotspot, retro-fitting a Yes Permeable Paving possibility at the properties to the south of Rowanwood Gardens. Flows should be managed between the A1 Yes Boundary Flow Interception and Coach Road. Potential for SLR site. Minimal properties located within the hotspot, retro-fitting a Yes Rainwater Harvesting possibility at the properties to the south of Rowanwood Gardens. Increase Sewer Capacity No sewer network within the hotspot. No Separation of foul/surface water No sewer network within the hotspot. No systems Drainage exists and maintenance is critical to Yes Improve maintenance regime reduce the risk in the area. Opportunities for storage along the A692, Flow/Storage on Roadway Yes Pathway Consett Road, Coach Road and the A1. Flows should be managed along Black Burn, along the A692, Consett Road, Coach Road, Yes Manage overland flows A1 and the pathway to the north of Black Burn. Black Burn could be increased in capacity to Yes Improve channel capacity alleviate the risk in Team Valley. Daylighting of Black Burn would allow more capacity and other measures such as Yes Open up culverts floodplain storage to be used. Could reduce the risk in Team Valley. Opportunities for floodplain storage Improve floodplain storage throughout the hotspot and to the south of Yes the hotspot. Remove obstructions/blockages at the Remove Obstructions culvert entrances, along Black Brook and the Yes undesignated watercourses. Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Gateshead or even nationally). Planning policies and development control Planning policies/development should be taken forward at a Council wide Yes control level for action, as opposed to at individual hotspot level. Receptor Receptor No development sites. Retro-fitting also Improve Resilience and resistance possibility and could be targeted at high risk Yes properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 2. Measures scoring over 75 have been highlighted as being appropriate for further consideration. AECOM Surface Water Management Plan 87
Capabilities on project: Water
Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 2: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 1 1 1 1 1 85 Yes
Soakaways/Infiltration NA NA
Attenuation/Storage 1 0 1 2 1 1 1 80 Yes
Swales/Filter Drain 2 0 1 1 1 2 1 90 Yes Source Source Permeable Paving 2 1 1 0 0 1 1 100 Yes
Boundary Flow Interception 1 0 1 1 -1 1 1 55 Maybe
Rainwater Harvesting 2 1 1 1 1 1 1 120 Yes
Increase Sewer Capacity NA NA Separation of foul/surface NA NA water systems Improve maintenance 1 1 0 0 0 0 0 55 Maybe regime Flow/Storage on Roadway 1 0 1 1 1 1 1 65 Maybe
Manage overland flows 1 0 1 1 -1 0 1 50 Maybe
Pathway Improve channel capacity 1 -2 0 -1 -1 1 -1 -70 No
Open up culverts -1 -1 1 2 -1 2 2 5 No Improve Floodplain 0 0 0 2 0 2 2 50 Maybe Storage Remove Obstructions 0 0 0 0 0 0 0 0 No
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / 1 1 1 0 0 1 1 80 Yes development control
Receptor Receptor Improve Resilience and 0 0 0 0 -1 1 0 0 No resistance
SLR Site To the north west of the hotspot, a SLR site is situated on the Whickham Hill Plantation. Due to the nature of the local topography it may be possible for surface water from Whickham Hill to reach the hotspot during extreme events. The true extent of this Whickham Hill acting as a source of water to the hot spot could be ascertained through hydraulic modelling. To ensure that any impact is managed it is recommended that the development of the SLR site implements source control measures to manage surface water runoff on site and does not connect into the combined sewer that exists in the vicinity. It will be necessary to provide sewer networks as part of the development however it is recommended that surface water should be managed on site rather than disposed of into the public sewer system. Road Infrastructure Critical infrastructure at risk of surface water flooding includes Coach Road and the A1. The source of the risk is from fluvial AECOM Surface Water Management Plan 88
Capabilities on project: Water flows entering from the west and flowing to Team Valley. One option would be to formally incorporate flood storage capacity into existing ponds outside of GH26 and the sports fields within GH26 in times of extreme events. However this would modify the existing social function from its existing usage into a more multifunctional area. An alternative is to provide and manage a formal and broader overland flow path to attenuate flows entering the Team Valley area. This could be achieved by providing a shallow drainage path through the existing fields. This would aim to reduce the flood risk in the location of the known incident in GH40. The benefit of this approach is that it would reduce flood risk within the heavily urbanised GH40 where limited space is available for flood storage. It would also present an opportunity for promoting biodiversity in the area and introducing other aesthetic benefits such as landscaping. This should be reviewed as a fluvial flood risk exercise to determine the benefits provided to downstream areas. Besides the culverted watercourse, there is no drainage infrastructure within GH26. The level of Gateshead Road and Coach Road should be investigated to ensure that the design water surface level at any flood storage measure is below the road. For the few properties within GH26, flood risk could be managed by ensuring they are above flood storage levels. This work should also check if improving resilience and resistance at individual properties is necessary.
Recommendations If the Partners were to undertake works to manage the risk of surface water flooding in hotspot GH26 the following Actions should be considered; GH26.1 – Gateshead Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. GH26.2 – Investigate benefit to GH40 (Team Valley Trading Estate) of providing storage within GH26. The River Team integrated Modelling Study should provide a greater insight into the issue. AECOM Surface Water Management Plan 89
Capabilities on project: Water AECOM Surface Water Management Plan 90
Capabilities on project: Water
Hotspot Ref: GH28 Hotspot Location: Birtley
Site Description The Birtley hotspot lies on the boundary between Gateshead and County Durham. Durham Road bounds the hotspot to the east and the east coast railway line to the west. Flowing north through GH28 is Rowletch Burn, an ordinary watercourse. The area is comprised of industrial warehouses, factories and depots on the right hand bank of Rowletch Burn which the land slopes gently towards. The industry comprises lots of impermeable surfaces in the form of roofs and car parks although they are interspersed by areas of waste land and playing fields which offer opportunities to manage surface water as does the ELR site in the area. Northumbrian Water Capital Works NWL are not undertaking any capital works in the area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The hotspot is located within Drainage Area 04-D11. The sewer data provided does not cover this drainage area. Gateshead Council Records of Flooding There are no known surface water incidents in the hotspot. Surface Water Flood Risk The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding correlate well with one another. There are 91 properties, one railway, one road and one police station which fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding show that there are a number of areas with a risk of ‘deep’ flooding within GH28. These areas of ‘deep’ flooding are associated with the depots, works and industrial estates located between the railway line and Durham Road (A1627). The source of surface water in this area is primarily from the impermeable surfaces throughout the urbanised area. There are flow pathways of shallow water entering the area from the east. The flow pathways from the east are sourced from Harras Bank and Station Lane. This source of surface water is primarily generated from the impermeable surfaces throughout the urbanised area. There are a number of areas at risk of flooding associated with the land to the west of the railway line. A number of flow pathways from the west develop from rural runoff into land drains (associated with Ouston Springs Farm), which then follow the local topography towards Rowletch Burn (ordinary watercourse). Rowletch Burn flows north along the east of the railway to the south of GH28 and there is a topographical low spot allowing deep pooling to the west of the railway line as the drains join Rowletch Burn. There are deep pools of surface water to the west of GH28, located to the west of the railway where there are local topographic lows. These pools are associated with Rowletch Burn where there is shallow surface runoff from Westline Industrial Estate and Station Lane. This source of surface water is primarily generated from the impermeable surfaces throughout the urbanised area. There is an additional deep pool of water to the north of the GH28 area associated with an artificial water body between the sewage treatment works and Keyline Builders Merchants. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 1. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 1. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 91
Capabilities on project: Water
Table 1: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? One ELR development site. Retro-fitting of Green Roofs Yes existing buildings is an option. Contaminated land and a high water table Soakaways/Infiltration are possible and will require geotechnical No investigation to determine feasibility. Opportunities for storage possible to the west Attenuation/Storage Yes of Rowletch Burn. Often used alongside roads, there are few
Source Source Swales/Filter Drain Yes potential opportunities for installation. A possibility in the ELR site and retro-fitting Permeable Paving Yes large hardstand/carpark areas. The external flow paths from the west could Boundary Flow Interception be intercepted and diverted away from flood Yes vulnerable areas in the hotspot. Retro-fitting of existing buildings has limited Rainwater Harvesting Yes potential, the ELR site has more potential. Sewer capacity not a known problem in the Increase Sewer Capacity Yes area. Limited information available. Sewer issues have not been recorded in the area, however more information required on Separation of foul/surface water the existing incidents as the main trunk of the Yes systems combined sewer runs under the main flow path and may be contributing to the risk. Drainage exists and maintenance is critical to Improve maintenance regime reduce the surface water risk. Yes Opportunities for storage in Station Lane but Flow/Storage on Roadway Yes Pathway open areas may be more suitable. The flow pathway crossing from the west to the area south of the ELR site could be diverted north along the western side of the Manage overland flows Yes railway to be formalised with storage areas investigated to minimise flood flows near flood vulnerable infrastructure. Possible but this may worsen flood risk in downstream areas of the Team Valley. Improve channel capacity Further investigation of impacts would be Limited required. Flood storage would reduce downstream impact. Open up culverts Road and rail infrastructure prevent this No The Green Infrastructure area west of the Improve floodplain storage Limited railway could become floodplain. Remove obstructions/blockages in the sewer Remove Obstructions Yes network possible but of minimal benefit Possible, but would need to be implemented Improved weather/flood warning as part of wider scheme (i.e. all of Limited Gateshead or even nationally). One ELR development sites within hotspot. However, planning policies and development Planning policies/development control should be taken forward at a Council Yes control wide level for action, as opposed to at
Receptor Receptor individual hotspot level. One ELR development site. Retro-fitting also Improve Resilience and resistance possibility and could be targeted at high risk Yes properties (i.e. deep flooding). AECOM Surface Water Management Plan 92
Capabilities on project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 2. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 2: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 1 1 1 -1 1 1 110 Yes
Soakaways/Infiltration NA NA Attenuation/Storage 2 1 1 2 1 1 1 135 Yes
Swales/Filter Drain 2 1 1 1 0 1 1 115 Yes Source Source Permeable Paving 2 1 0 0 0 1 1 85 Yes
Boundary Flow Interception 1 1 0 0 0 0 0 55 Maybe
Rainwater Harvesting 2 1 1 0 1 1 1 105 Yes
Increase Sewer Capacity 1 -1 -1 0 -2 -1 -2 -55 No Separation of foul/surface 1 0 1 1 -2 1 1 50 water systems Maybe Improve maintenance 2 1 0 0 2 -1 0 80 Yes regime Flow/Storage on Roadway 2 1 1 1 1 1 1 120 Yes
Manage overland flows 2 2 1 1 -1 1 1 145 Yes
Pathway Improve channel capacity 1 -1 1 1 60 Maybe
Open up culverts NA NA Improve Floodplain 1 -1 2 2 100 Storage Yes Remove Obstructions -1 1 1 1 0 1 1 55 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / 1 1 0 1 0 1 1 80 development control Yes
Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance AECOM Surface Water Management Plan 93
Capabilities on project: Water
ELR and Works Area The large amount of impermeable area (roofs and hardstand) generates considerable runoff on the eastern area of the railway line. The existing sports field and open area is at risk of flooding. Development of the ELR site in the existing open area would further increase the amount of impermeable surfaces and worsen the existing flood risk. One option would be to utilise the site in times of extreme events. However this would prevent development. The ELR site is currently derelict and at its western extent has naturally developed into a wetland habitat (see photo right) which will be providing biodiversity benefits on the edge of strategic green infrastructure and be acting as a store for excess surface water runoff. It would be possible to formalise this area as a wetland and actively seeking to expand the green area to cover the whole site thereby providing benefits to the wider area. Incorporated into future capital renewal surfacing works, roads and hardstanding could be re-profiled to provide overland flow paths away from vulnerable assets to the storage area. If developed the ELR site should seek to utilise the existing wetland area to manage surface water for the benefit of as wide an areas as possible. Gateshead Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development site presents opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where combined sewers exist, development ought to remove surface water from the combined system. The playing fields in the area could be landscaped so that they act as a natural low point that would collect excess surface water thereby alleviating the risk to the surrounding buildings. Retro-fitting of green roofs, rainwater harvesting and permeable paving may also be possible. There may be restrictions on the public sewer capacity, any additional capacity would need to be accommodated by the developer. Rowletch Burn Rowletch Burn flows in a northerly direction through the hotspot before joining the River Team. The flood maps suggest that a culvert underneath the railway line could be a restriction to flow and cause water to back up affecting the low lying land on the right hand bank; ELR site and sports ground. It may be possible to alleviate this through improving the condition of the watercourse. This could be increasing the channel capacity, upstream floodplain storage or removing any obstructions. There is an opportunity to use the available open space on the western side of the railway line as a flow path and flood storage area. This would alleviate the risk and promote biodiversity alongside the railway line in the green infrastructure area. Alternatively further upstream, the Birtley Union Brickworks Local Wildlife Site may offer opportunities for additional floodplain storage. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations GH28.1 – Gateshead Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. Modelling of Rowletch Burn would prove beneficial to understanding the wider flood risk from the watercourse and which measure might be feasible to manage the risk. GH28.2 – If the ELR site does not get developed, Gateshead Council should look into the possibility of formalising it as a green space with capability to store excess surface water runoff from the surround area building on the wet habitat that has already developed. AECOM Surface Water Management Plan 94
Capabilities on project: Water AECOM Surface Water Management Plan 95
Capabilities on project: Water
Hotspot Ref: GH42 Hotspot Location: Dunston
Site Description The Dunston hotspot is centred upon Ravensworth Road which is on the left hand bank of the River Team, just upstream of its confluence with the River Tyne. Consequently water levels in the River Team are influenced by the tide. The area is densely urbanised with residential and commercial properties meaning there is little open space. The area is a mix of development dating from after the war, the early 1960s and some redevelopment having occurred 10-15 years ago. Large scale re-development is expected to take place in the future with housing sites in the area. Northumbrian Water Capital Works NWL are to undertake capital works along Ravensworth Road in Dunston. During heavy rainfall the combined sewers in the Ravensworth Road area surcharge, resulting in flood water escaping from the sewer system, causing highway, external and internal property flooding. The proposed solution will reduce the risk of internal property flooding by transferring flows to points where there is available capacity within the existing sewer network. In the northern area of Ravensworth Road approximately 275m of new sewer pipes will be constructed in the road to the rear of Victoria Bungalows, and into Ravensworth Road increasing in size from 450 to 750mm diameter pipes. For the southern area of Ravensworth Road approximately 300m of new sewers will be constructed transferring flows from Ravensworth Road and Festival Way into Ellison Road increasing in size from 300 to 1200mm diameter. Works on site are programmed to commence after the demolition of Derwent Tower Estate, in mid August 2012 for completion in January 2013. The new sewers in the northern and southern parts of Ravensworth Road will carry combined surface water and foul flows and ultimately drain to Howdon STW via the Tyneside Interceptor Sewer. The connection points to the Interceptor Sewer are close to existing Combine Sewer Overflow points; under flood conditions the sewer system will “overflow” into the River Team. NWL are designing the works to provide protection against flooding up to the 1 in 40 year rainfall event. There will continue to be a residual risk of flooding from rainfall events that exceed the 1 in 40 year event. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. DA to cope with rainfall events and identify DAs with the greatest hydraulic risk.
Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic Housing Land resulting from planned growth and identify DAs Availability with the greatest increase in demand resulting Assessments (up to from new development. 2020) and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
The hotspot is located within the Dunston, Teams Drainage Area, and the analysis results for this Drainage Area are detailed in Table 2. As Table 2 shows, the overall priority of the Dunston, Teams Drainage Area is 18 out of 58 Drainage Areas. AECOM Surface Water Management Plan 96
Capabilities on project: Water
Table 2: Dunstan Drainage Area Analysis Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) Local DA Location Growth Authority Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon)
Dunstan, Gateshead 05-D13 35 28 12 23 98 18 Teams MBC
* Based on data provided 19th November 2010
Gateshead Council Records of Flooding There are five recorded flood incidents, four along Ravensworth Road (6-7/11/2000, 17/07/2007, 6-7/09/2008 and 31/03/2010) and one at Tower Court (6-7/11/2000). The 2007 surface water incident was caused by excessive rainfall. The other incidents along Ravensworth Road can be attributed to inadequate sewer system and the carriageway conveying flows. The cause for the surface water incident at Tower Court can also be attributed inadequate capacity in the sewer system as well as the footway conveying flows. This area is also at risk from tidal flooding. The risk of flooding is ‘High’ at Tower Court and ‘Medium’ at Ravensworth Road. There is an interaction between the sewer system and the River Team/Tyne. The area is next to the River Team and just upstream of the confluence with the River Tyne. When water levels are high in the Team, either because the Team is in flood or there is a high tide in the Tyne the sewers are unable to discharge. A number of sewers come together in this area and meet the interceptor sewer which overflows into the Team. When the overflow can’t discharge because of high river levels the system surcharges and floods. The sewer network within the site has both combined and separate sewers. Surface Water Flood Risk The Flood Map for Surface Water and the Areas Susceptible to Surface Water Flooding correlate well with the reported incidences located within the GH42 hotspot and show two areas of deep flooding to the north and south of the hotspot. The source of surface water flooding is most likely a combination of both; (i) the impermeable surfaces throughout the urbanised area, and (ii) tidal locking of drainage in GH42 due to the River Team. It appears that there may be a flow pathway originating near Church Street and Seymour Street to the west, entering an area of low lying land where Clockmill Road has disrupted the flow path to the River Team. The source of surface water in this area is likely to be from the impermeable surfaces throughout the urbanised area. The area of deep water to the south of the area is pooled within the Co-Ops car park off Ravensworth Road, and the Post Office access road located off Ellison Road. The source of surface water in this area is primarily from the impermeable surfaces throughout the urbanised area. 102 properties fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 97
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Potential for housing development site and Green Roofs Yes retro-fitting existing buildings. Close to the River Tyne, high water table Soakaways/Infiltration No likely requires geotechnical investigation Attenuation/Storage Opportunities for storage could be possible. Yes Often used alongside roads, and there are Swales/Filter Drain potential opportunities for Ravensworth Yes Road. Source Retro-fitting a possibility along the main flow Permeable Paving Yes path. Further investigation required. No major external flow paths that influence Boundary Flow Interception No hotspot. Retro-fitting of existing buildings a limited Rainwater Harvesting Yes option. Northumbrian Water undertaking works in Increase Sewer Capacity Yes the area. Sewer issues have been recorded in the Separation of foul/surface water area, as part of future development surface Yes systems water can be removed from the combined sewers. Drainage exists and maintenance is critical to Improve maintenance regime reduce the surface water risk. Yes Opportunities for storage at the north of the Flow/Storage on Roadway Yes site in Wellington Road and Festival Way.
Pathway Flowpaths are limited and along existing Manage overland flows Yes roads. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove obstructions/blockages in the sewer Remove Obstructions Yes network possible but of minimal benefit Possible, but would need to be implemented Improved weather/flood warning as part of wider scheme (i.e. all of Limited Gateshead or even nationally). Housing development site within hotspot and so planning policies and development control Planning policies/development should be taken forward at a Council wide Yes control level for action, as opposed to at individual hotspot level. Receptor Receptor Housing development sites should incorporate Resilience Measures. Retro- Improve Resilience and resistance fitting also possibility and could be targeted Yes at high risk properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 98
Capabilities on project: Water
Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 1 1 1 0 1 1 115 Yes
Soakaways/Infiltration NA NA
Attenuation/Storage 2 1 1 2 1 1 1 135 Yes
Swales/Filter Drain 1 0 0 2 1 2 1 70 Maybe Source Source Permeable Paving 2 1 0 0 -1 1 1 80 Yes
Boundary Flow Interception NA NA
Rainwater Harvesting 2 1 1 0 1 1 1 105 Yes
Increase Sewer Capacity 2 1 1 0 1 0 0 95 Yes Separation of foul/surface 1 1 1 0 1 0 2 85 water systems Yes Improve maintenance 2 0 0 0 1 0 1 50 Yes regime Flow/Storage on Roadway 2 1 1 1 1 1 1 120 Yes
Manage overland flows 2 2 1 1 -1 1 1 145 Yes
Pathway Improve channel capacity NA NA
Open up culverts NA NA Improve Floodplain NA Storage NA Remove Obstructions -1 1 1 1 0 1 1 55 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / 1 1 0 1 0 1 1 80 development control Yes
Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Site Gateshead Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where combined sewers exist, development ought to remove surface water from the combined system. Ravensworth Road Tide locking of the sewer system is the key problem for hotspot GH42 that is not going to go away. The north end of Ravensworth Road is the low point and at risk from deep surface water flooding caused by heavy rain. Where possible the excess surface water should be stored within the roadway. Flood storage and an overland flow path into the River Team should be investigated although Clockmill Road would make a connection difficult and the flow path could also provide a low spot where high tides could ingress. Incorporated into future capital renewal surfacing works, this would involve roadway re-grading and profiling of the road AECOM Surface Water Management Plan 99
Capabilities on project: Water profile to provide overland flow paths away from vulnerable areas. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations GH42.1 – Gateshead Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. GH42.3 – As part of highways maintenance programme, explore potential for storing water in roads. AECOM Surface Water Management Plan 100
Capabilities on project: Water AECOM Surface Water Management Plan 101
Capabilities on project: Water
Hotspot Ref: GH52 Hotspot Location: Old Fold
Hotspot Description The Old Fold hotspot is located in the north east of Gateshead and covers a relatively small area either side of the A184 (Abbotsford Road), a major highway route. The areas at risk of surface water flooding are residential housing to the south of the A184 and the road itself. An area of strategic green infrastructure and a green infrastructure opportunity area are located to the north of the A184. The housing estates and A184 are interspersed by open areas which may present opportunities to manage surface water flooding. There are also a number of housing sites and the Brandling Neighbourhood Plan Area in close proximity to the areas at risk which offer opportunities to manage surface water, particularly those located upstream of the risk areas. Northumbrian Water Capital Works NWL are not undertaking any capital works in the area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. DA to cope with rainfall events and identify DAs with the greatest hydraulic risk. Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic Housing Land resulting from planned growth and identify DAs Availability with the greatest increase in demand resulting Assessments (up to from new development. 2020) and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
The hotspot is located within the Friars Goose Drainage Area, and the analysis results for this Drainage Area are detailed in Table 2. As Table 2 shows, the overall priority of the Friars Goose Drainage Area is 34 out of 58 Drainage Areas. AECOM Surface Water Management Plan 102
Capabilities on project: Water
Table 2: Friars Goose Drainage Area Analysis* Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) Local DA Location Growth Authority Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon)
Gateshead 05-D21 Friars Goose 53 32 18 16 119 34 MBC
* Based on data provided 19th November 2010 Gateshead Council Records of Flooding Two known incidents dated 6-7/11/2000 and 6-7/09/2008 are located along Felling Bypass (A184) in Old Fold. The cause is attributed to extreme rainfall exceeding the capacity of the sewer system combined with the carriageway conveying surface water. The risk of flooding has been categorised as ‘medium’. This area has been covered by the Tyneside Sewerage Study (although it covers a much larger area) and they are now doing a second stage study. Surface Water Flood Risk The Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding correlate well with the two reported incidences located on the A184, showing flooding at two locations on the A184. An area at risk from ‘deep’ surface water flooding to the south of the A184 is centralised on the residential properties located on Green Lane Gardens and the northern end of Eastwood Gardens. The source of surface water in this area is primarily from the impermeable surfaces throughout the urbanised area. The local topography slopes south to north and Green Lane Gardens and the A184 lie at the bottom of the slope therefore will collect runoff coming down the hill. Additionally, there are pockets of isolated flooding on Pensher Street East, Friary Gardens, Lobelia Avenue and Acacia Road. These are probably associated with the impermeable nature of the area and localised depressions. The area of deep water to the north of the A184 is around Coach Road Green and Burlison Gardens. The source of surface water in this area is runoff from the impermeable surfaces and rural fields and could be coming across the A184 from the Green Lane Gardens and Brandling areas. A flow pathway originates in the Brandling Neighbourhood Plan Area and affects the A184 before continuing on to Burlison Gardens. Approximately 146 properties fall within the Flood Map for Surface Water - 200 year Shallow and Areas Susceptible to Surface Water Flooding - Intermediate Susceptibility extents. The A184 road is critical infrastructure which would benefit from surface water measures to mitigate the surface water risk within the GH52 hotspot. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 103
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Development sites located to the south and Green Roofs south east of the hotspot. Retro-fitting of Yes existing buildings unlikely to be an option. Close to the River Tyne, high water table Soakaways/Infiltration No likely requires geotechnical investigation. Opportunities for storage could be possible Attenuation/Storage Yes along Green Lane Gardens. Often used alongside roads, and there are
Source Source potential opportunities for installation east of Swales/Filter Drain Yes Coach Road Green and in the Green Lane Gardens (Path) area along the A184. Retro-fitting a possibility but should be Permeable Paving Yes utilised on development sites. Flow path from Brandling Neighbourhood Boundary Flow Interception Yes Plan Area could be managed. Development sites present opportunities. Rainwater Harvesting Yes Retro-fitting unlikely to be an option. Sewer capacity not a known problem in the Increase Sewer Capacity Yes area. Open space could facilitate expansion. Area served by combined sewers; Separation of foul/surface water development presents opportunities to Yes systems separate the system. Drainage exists and maintenance is critical to Improve maintenance regime reduce the surface water risk. Yes
Flow/Storage on Roadway Opportunities for storage in residential roads. Yes Pathway
Flow paths exist and should be managed or Manage overland flows Yes formalised. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove obstructions/blockages in the sewer Remove Obstructions Limited network possible but of minimal benefit. Possible, but would need to be implemented Improved weather/flood warning as part of wider scheme (i.e. all of Limited Gateshead or even nationally). No development sites within hotspot. However, planning policies and development Planning policies/development control should be taken forward at a Council Yes control wide level for action, as opposed to at
Receptor Receptor individual hotspot level. No development sites. Retro-fitting also Improve Resilience and resistance possible and could be targeted at high risk Yes properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 104
Capabilities on project: Water
Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 1 1 1 0 1 1 115 Yes
Soakaways/Infiltration NA 0 NA
Attenuation/Storage 2 2 -1 2 1 1 1 140 Yes
Swales/Filter Drain 2 1 0 1 1 2 1 110 Yes Source Source Permeable Paving 2 1 0 0 -1 0 2 80 Yes
Boundary Flow Interception 2 1 -1 0 0 1 1 70 Maybe
Rainwater Harvesting 2 1 1 0 1 1 1 105 Yes
Increase Sewer Capacity -1 -2 0 0 -2 -1 -2 -115 No Separation of foul/surface 2 1 0 1 0 1 2 105 water systems Yes Improve maintenance 2 0 0 0 2 0 1 55 Maybe regime Flow/Storage on Roadway 2 1 -1 0 1 1 1 75 Maybe
Manage overland flows 2 2 0 1 -1 1 1 130 Yes
Pathway Improve channel capacity NA 0 NA
Open up culverts NA 0 NA Improve Floodplain NA 0 Storage NA Remove Obstructions -1 1 1 1 0 1 1 55 Maybe
Improved weather warning 1 0 0 0 0 2 2 40 Maybe Planning policies / 1 1 0 1 0 1 1 80 development control Yes
Receptor Receptor Improve Resilience 1 2 -1 0 -1 1 1 80 Yes
Development Sites Gateshead Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development sites are located uphill of the areas at risk and are likely to be acting as sources of surface water; as such they present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. The sites are also currently served by combined sewers; re-development ought to remove surface water from the combined system. Green Lane Gardens The northern end of Eastwood Gardens and Green Lane Gardens are located in a topographic sink, at the foot of a hill that slopes up Eastwood Gardens to the south, as such it is at risk from flooding caused by heavy rain running off the impermeable surfaces and flowing down Eastwood Gardens. Managing the overland flows and diverting them into swales or storage areas located in nearby multifunctional open space that exists between Green Lane Gardens and the A184 (see photo right) could be used to alleviate AECOM Surface Water Management Plan 105
Capabilities on project: Water
the risk. There may be opportunities to provide storage in the road along Green Lane Gardens. There may be opportunities to provide storage along road Pensher Street, Friary Gardens and Acacia Road. Incorporated into future capital renewal surfacing works, this would involve roadway re-grading and profiling of the roads to store excess water. A184 (Abbotsford Road) The A184 (Abbotsford Road) represents critical infrastructure at risk of surface water flooding. The source of the risk is runoff down Eastwood Gardens and from the Brandling Neighbourhood Plan Area. The measures suggested to protect the Green Lane Gardens area and the measures suggested for the Brandling Neighbourhood Plan Area should benefit the A184. Burlison Gardens The open land around Coach Road Green and Burlison Gardens appears to be a low point that would collect surface water runoff. The open land acts as a natural storage are for the water and could be landscaped to be able to provide more storage. Alternatively water could be stored in the roads to prevent it affecting properties. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Gateshead or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations GH52.1 – Gateshead Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments and surface water to be removed from the combined sewer system. GH52.2 – Assess the viability of utilising Green Lane Gardens as a storage area in times of extreme events and providing a formal overland flow path to channel water into the storage area. GH52.3 – As part of highways maintenance programme, explore potential for storing water in roads and channelling it to storage areas. AECOM Surface Water Management Plan 106
Capabilities on project: Water Appendix D– Newcastle Hotspot Data Sheets AECOM Surface Water Management Plan 108
Capabilities on project: Water
Hotspot Ref: NH09 Hotspot Location: Brunton
Site Description The Brunton hotspot lies within the catchment of the Ouseburn which drains through Newcastle to the River Tyne. The Ouseburn is a designated Main River and consequently falls under the responsibility of the Environment Agency and outside the remit of a SWMP. However the Ouseburn has several tributaries that do fall within the remit of a SWMP in light of them being the responsibility of the local authority or riparian owners. Consequently this interaction means that the Ouseburn is highly relevant to the NewcastleGateshead SWMP. The Ouseburn could be considered to be “full” in that it would struggle to receive any additional runoff without an associated increase in the flood risk. During rainfall events the Ouseburn exhibits a double flood peak as a result of runoff from the catchment and surface water runoff from sewers. Additionally a number of bridges crossing the Ouseburn cause flood flows to back up behind them raising water levels. Newcastle City Council has raised and widened two of these bridges and are working with the Environment Agency to raise a third. The combination of the double flood peak and the restrictive bridges causes prolonged periods of high water levels in the Ouseburn which can inhibit the ability of surface water sewers to discharge causing the sewer system to surcharge leading to surface water flooding. Subsequently, Newcastle City Council have raised and widened two bridges downstream of Three Mile Bridge, and the council is working with the Environment Agency to raise a footbridge at Acomb Crescent. The Environment Agency has subsequently identified that any reduction in runoff volumes will benefit flood risk and provided Newcastle City Council with funding to undertake a study to review the potential for storing water on the tributaries of the Ouseburn. One such tributary is Newbiggin Burn which flows in a north easterly direction, through Kingston Park, before joining the Ouseburn (see map right). Newbiggin Burn disappears below ground at several points along its length, and is culverted in several sections through the hotspot. Newbiggin Burn is an undesignated watercourse, and consequently falls to the riparian land owners to manage although Newcastle City Council has permissive powers to undertake works. The Brunton hotspot itself covers a very large area in Gosforth, stretching from Kingston Park in the west through Fawdon and Brunton Park to Whitebridge Park in the east. The City of Newcastle Golf Club is a large areas of green open space within the hotspot. Several large sites have been identified as suitable for housing development within the hotspot, including sites to the north of Kingston Park Road, to the north of the City of Newcastle Golf Club and to the south of High Gosforth Park. Strategic green infrastructure opportunities and green infrastructure opportunity areas have been identified within the hotspot, along the Ouseburn corridor. Northumbrian Water Capital Works Northumbrian Water completed a flood alleviation scheme in Acomb Crescent in 2006/7 within the Red House Farm area of the City, which is located to the west of the City of Newcastle Golf Club. In June 2005 a large number of properties flooded in this area and investigations undertaken by Northumbrian Water identified the risk of flooding to properties was greater than one in ten years (greater than one in five years for several properties). Based on the high flood risk in the Brunton Park area, Northumbrian Water prioritised this problem for investment and is in the process of establishing the true extent of the problem and identifying a number of alleviation options. Northumbrian Water has also installed flood boards at a number of properties in the Brunton Park area to reduce the impact of flooding that may occurs until the construction phase of preferred alleviation scheme is completed. Northumbrian Water is in discussions with the Environment Agency regarding consents for new overflows along Princes Road in Brunton Park, and also the possibility of a joint project with the Environment Agency and Newcastle City Council. Newcastle City Council is providing a presence and support to the project team to provide assistance where possible. The City Council is not currently in a position to provide any funding for capital works. AECOM Surface Water Management Plan 109
Capabilities on project: Water
Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area.
Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. DA to cope with rainfall events and identify DAs with the greatest hydraulic risk. Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic Housing Land resulting from planned growth and identify DAs Availability with the greatest increase in demand resulting Assessments (up to from new development. 2020) and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
The hotspot is located within the Gosforth Drainage Area, and the results for this Drainage Area are detailed in Table 2. The overall priority of the Gosforth Drainage Area is 5 (out of 58 total Drainage Areas). The priority ranking of 5 highlights that Northumbrian Water is concerned about the sewerage network in the Gosforth area, and managing this sewer network in the future. Managing surface water within the hotspot area can therefore be considered an important issue going forward. Table 2: Gosforth Drainage Area Analysis Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without weighting) Local DA Location Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle 05-D31 Gosforth Upon Tyne 4 11 15 29 59 5 City Council * Based on data provided 19th November 2010
Newcastle City Council Records of Flooding There are twenty four recorded incidents of historic flooding within the hotspot, with clusters of incidents occurring in the Fawdon and Brunton Park areas. There are seven recorded incidents of flooding in the Brunton Park area, which are recorded to have occurred on the 4th June 2000, the 6th November 2000 or the 6th September 2008. The 2000 and 2008 flooding in this area has been attributed to heavy rainfall, overflow from storm drains and flooding from the Ouseburn. There are fourteen recorded incidents of flooding in the Fawdon area, notably along Acomb Crescent and around Larchwood Avenue. Flooding is recorded to have occurred in the Fawdon area on the 25th August 1999, 21st October 2005, 30th June 2005 and the 1st April and 6th September 2008. Flooding in the Fawdon area has been attributed to heavy rainfall, AECOM Surface Water Management Plan 110
Capabilities on project: Water overflow from storm drains and blocked drainage systems. In response to the flooding in the Acomb Crescent area, some storage has been installed in a grass verge to help alleviate the problem. In addition to the twenty one flood incidents in the Fawdon and Brunton Park areas, there are three other recorded incidents of flooding occurring in the hotspot. One of these three incidents occurred in 2008 in the Whitebridge Park area, to the east of the hotspot. Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, there appears to be several areas at risk throughout the hotspot. The main overland flow pathway through the hotspot is along the Ouseburn, which is fluvial flooding in nature and is sourced from the Environment Agency Main River. In the west of the hotspot, there is a flow path along Newbiggin Burn, from Kingston Park in the south west, through Fawdon Walk. In the centre of the hotspot, there appears to be an overland flow path along a second undesignated watercourse that flows through the City of Newcastle Golf Club. To the west of the City of Newcastle Golf Club, Acomb Crescent and Farne Avenue are affected by surface water flooding as is the A1, to the south of the Ouseburn. The main areas of surface water ponding occur along the overland flow path routes through the hotspot. In the north flooding in Brunton Park correlates with the recorded flood incidents in the area. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 987 properties are at risk of flooding within the hotspot. One critical infrastructure location is also shown to be at risk of flooding within the hotspot; the A1 to the north of the Kingston Retail Park and the south of Kingston Park Road. Based on the Environment Agency’s Flood Map for Surface Water (deep), there are a number of locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. The areas that could potentially flood to depths greater than 0.3m are generally located along the main overland flow pathway routes though the hotspot detailed above. The A1 is predicted to be at risk from flood depths exceeding 0.3m to the north and south of Kingston Park Road. Previous flood incidents within the hotspot have been attributed to heavy rainfall, overflow from storm drains, blocked drainage systems, and flooding from the Ouseburn. The overland flow pathways and areas of surface water ponding within the hotspot are therefore considered to be product of rainfall on impermeable areas and overwhelmed drainage systems, including ordinary watercourses such as Newbiggin Burn. High water levels within the Ouseburn are known to impede drainage systems that discharge into it, for example the Acomb Crescent and Brunton Park areas are affected by surcharging sewers when water levels in the Ouseburn are high. Whilst the Kingston Park area is not shown to be at risk based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, it is a known source of surface water that significantly affects the flood risk in the Ouseburn. The North Gosforth Integrated Urban Drainage Pilot Study estimates that in July 2007 the Kingston Park area contributed almost 80% of the total river flow in the Ouseburn. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 111
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing sites. Potential for Green Roofs existing residential, commercial and Yes industrial development. Ouseburn flows through hotspot. High water Soakaways/Infiltration No table likely to make infiltration unfeasible. Possibility for housing sites. Also potential to install attenuation storage within available Attenuation/Storage Yes green areas, including Kingston Park, Bent Hill and the City of Newcastle Golf Club.
Source Source Often used alongside roads, potential Swales/Filter Drain opportunities including Kingston Retail Park, Yes Acomb Crescent and Farne Avenue. Possible for housing sites. Retro fitting also a Permeable Paving possibility, particularly in car parking areas Yes within hotspot. Boundary Flow Interception N/A No Rainwater Harvesting Possible for housing sites and retro fitting. Yes The overall priority of the Gosforth Drainage Area, which the hotspot is located within, is Increase Sewer Capacity Yes relatively high. Increasing sewer capacity therefore warrants consideration. Limited potential, the sewer network in the Separation of foul/surface water hotspot is mainly made up of separate foul Limited systems and surface water sewers. A number of flood incidents within the hotspot are known to be a result of localised problems with drainage systems. The Improve maintenance regime Newbiggin Burn culverts are not to be Yes maintained and could cause problems. Improved maintenance is therefore key to managing surface water. Potential opportunities for storage along Flow/Storage on Roadway several roads within the hotspot including Yes Acomb Crescent and Farne Avenue. Flows could potentially be directed to, and managed within Kingston Park, Bent Hill, City of Newcastle Golf Club and other smaller
Pathway Pathway Manage overland flows Yes areas of green space available within the hotspot (smaller parks, playing fields, allotment gardens etc). Many parts of the Newbiggin Burn channel Improve channel capacity are known to be overgrown with vegetation Yes and choked with litter. Newbiggin Burn is culverted in several Open up culverts Yes locations. Newbiggin Burn provides opportunities to Improve floodplain storage Yes store water in areas of open green space. Many parts of the Newbiggin Burn channel Remove Obstructions Yes are known contain obstructions. Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally). Possibility for development sites within hotspot. Planning policies and development Planning policies/development control should be taken forward at a Council Yes control wide level, as opposed to at individual
Receptor Receptor hotspot level. Possibility for housing sites. Retro fitting also Improve Resilience and resistance possibility and could be targeted at high risk Yes properties (i.e. deep flooding). AECOM Surface Water Management Plan 112
Capabilities on project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 2 2 1 2 2 125 Yes
Soakaways/Infiltration N/A
Attenuation/Storage 2 2 1 2 1 1 1 170 Yes
Swales/Filter Drain 1 1 0 2 1 2 1 105 Yes Source Source Permeable Paving 2 1 1 0 -1 1 1 95 Yes
Boundary Flow Interception N/A
Rainwater Harvesting 2 0 1 1 1 2 2 95 Yes
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 1 -1 -2 1 -2 1 -1 -40 No water systems Improve maintenance 2 2 1 1 0 0 1 145 Yes regime Flow/Storage on Roadway 1 1 0 1 1 1 1 85 Yes
Manage overland flows 1 2 1 1 -1 1 1 125 Yes
Pathway Improve channel capacity 1 2 1 1 -1 1 1 125 Yes
Open up culverts 1 2 1 2 -1 1 2 145 Yes Improve Floodplain 1 2 1 1 -1 1 1 125 Yes Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
The majority of mitigation measures have been identified as being potentially appropriate within this hotspot which is a function of the size of the hotspot and different measures being applicable in different areas. If a more detailed study were undertaken on a small part of the hotspot the number of applicable measures would likely reduce. Based on the size of the hotspot, source and pathway measures have been discussed with reference to specific areas within the hotspot, whereas receptor measures are considered for the hotspot as a whole. AECOM Surface Water Management Plan 113
Capabilities on project: Water
Development Sites Given the large size of hotspot NH09, it is not surprising that a large number of housing sites fall within and in close proximity to its boundary. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The housing sites all present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. These measures would have the benefits of contributing to the green infrastructure network in the Brunton area and storage areas could explore the potential to provide additional storage for the Ouseburn when it is in flood Newbiggin Burn It is recommended that attenuation storage on Newbiggin Burn is subject to further investigation as an appropriate source control mitigation measure within the hotspot. Newbiggin Burn is a tributary of the Ouseburn, and providing storage on the Burn could limit the volume and speed with which water gets into the Ouseburn. Newcastle City Council have received local levy funding to undertake a study to identify potential locations for storing water on the Ouseburn tributaries, and it is recommended the Council uses this funding to undertake a detailed assessment of the Newbiggin Burn and potential flood alleviation options. There could also be opportunities to open up culverts, improve the channel capacity, floodplain storage and maintenance regime and remove obstructions. (It should be noted that local levy funding is not guaranteed in the future). It is anticipated that the detailed assessment would start with a walkover survey recording the condition of the watercourse and structures in an Asset Register, engaging with local residents and reviewing the potential to store water. Topographic survey and hydraulic modelling may ultimately be required to assess different measures. Based on the fact Newbiggin Burn flows through several culverts that are known not to be maintained (the photo right illustrates a culvert completely blocked by utility pipes), and that many parts of the Burn channel are overgrown with vegetation and choked with litter, an improved maintenance regime has also been suggested for Newbiggin Burn. In one location a property owner has built their boundary fence across the watercourse (photo below right). Any improvement in the condition of the burn would require co-ordinated management and integrated with a storage scheme since simply improving conveyance would increase the speed with which water got into the Ouseburn. If the riparian owners could be encourage to maintain Newbiggin Burn it would provide additional storage opportunities. Water could potentially be stored in the open channel lengths with the culverts providing the necessary throttles holding water back from the Ouseburn. This could be considered as part of the detailed assessment of the Newbiggin Burn and potential flood alleviation options on the Burn. As part of an improved maintenance regime, it is recommended that Newcastle City Council ensure that all of the culverts and crossings of Newbiggin Burn are entered on their Asset Register of structures capable of posing a flood risk. Kingston Park Although the Kingston Park area is not shown to be at risk based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, it is capable of contributing significant volumes of surface water to the Ouseburn and experiences surface water flooding on a regular basis. Managing this surface water at its source within the Kingston Park area may reduce the flood risk from the Ouseburn and in the immediate locality. Providing attenuation storage within the Kingston Park area (i.e. tanks under roads and car parks and multifunctional green area to north of the Metro line) is suggested as a potential source control measure, as is retro-fitting permeable paving in the large expanses of car parks, green roofs, swales/filter drains and rainwater harvesting. These would require further investigation to assess their potential. Newcastle City Council is currently working with the Environment Agency to identify suitable locations to retro-fit SuDS (e.g. attenuation storage). The installation of source control and surface water pathway mitigation measures has the potential to provide substantial reductions in surface water runoff from the site. AECOM Surface Water Management Plan 114
Capabilities on project: Water
Acomb Crescent Area Northumbrian Water completed a flood alleviation scheme in Acomb Crescent in 2007, detailed in Section 1.2. Additional measures that could be implemented would be holding water in the roads or landscaping the open space next to the Ouseburn to collect and hold excess runoff. 80m3 of storage has recently been installed in Acomb Crescent using Defra Early Action funding to reduce the risk of sewers surcharging when water levels in the Ouseburn are high. A1 The A1 is predicted to be at risk of surface water flooding between Kingston Retail Park and Kingston Park Road. Drainage from the A1 currently goes into the Ouseburn. If mitigation measures were to be implemented, which could be extremely expensive, the surface water would need to be managed as overland flows to reduce the risk to this section of critical infrastructure. Subsequently some means of storing the water would be required before it discharged into the Ouseburn. Brunton Park The housing site within the Brunton Park area offers significant potential to manage surface water through the implementation of source control measures potentially providing benefits to the wider area. If part of the site can be set aside as a storage area, runoff from elsewhere in Brunton Park could be channelled overland into this area rather than affecting properties. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH09.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH09.2 – Newcastle City Council to undertake detailed investigation of Newbiggin Burn and other tributaries of the Ouseburn with a view to providing storage and slowing the speed with which water gets into the Ouseburn. NH09.3 – Newcastle City Council to undertake walkover survey of Newbiggin Burn and enter all structures in the Asset Register. NH09.4 – Partners to work together to achieve improved surface water management within Kingston Park. AECOM Surface Water Management Plan 115
Capabilities on project: Water AECOM Surface Water Management Plan 116
Capabilities on project: Water
Hotspot Ref: NH11 Hotspot Location: Gosforth
Site Description Hotspot NH11 covers part of Gosforth and lies within the catchment of the Ouseburn which drains through Newcastle to the River Tyne. The Ouseburn is a designated Main River and consequently falls under the responsibility of the Environment Agency and outside the remit of a SWMP. However the Ouseburn has several tributaries that do fall within the remit of a SWMP in light of them being the responsibility of the local authority or riparian owners. Consequently this interaction means that the Ouseburn is highly relevant to the NewcastleGateshead SWMP. The Ouseburn could be considered to be “full” in that it would struggle to receive any additional runoff without an associated increase in the flood risk. During rainfall events the Ouseburn exhibits a double flood peak as a result of runoff from the catchment and surface water runoff from sewers. Additionally a number of bridges crossing the Ouseburn have caused flood flows to back up behind the bridges raising water levels. The combination of the double flood peak and the restrictive bridges causes prolonged periods of high water levels in the Ouseburn which inhibit the ability of surface water sewers to discharge causing the sewer system to surcharge leading to surface water flooding. The Environment Agency has subsequently identified that any reduction in runoff volumes will benefit flood risk and provided Newcastle City Council with funding to undertake a study to review the potential for storing water on the tributaries of the Ouseburn. Devils Burn (or Crag Hall Dene) is a tributary of the Ouseburn which flows across the north of Nuns Moor and into the hotspot at Dukes Moor. The watercourse disappears below ground at several points along its length. It is culverted under the Great North Road (B1318), to the east of which it returns to an open channel for approximately 100m (adjacent to Lodore Road) before going back into culvert until its confluence with the Ouseburn. Devils Burn is an undesignated watercourse, and consequently falls to the riparian land owners to manage although Newcastle City Council has permissive powers to undertake works. The surface water hotspot itself covers a very large area of Gosforth, stretching from Fawdon in the west to South Gosforth in the east. It encompasses Metro lines and stations, schools and is highly urbanised with little open space. Four small sites have been identified as suitable for housing development within the hotspot, on Christon Road, Ivy Road, the Meadows and near Fawdon Metro station. Strategic green infrastructure opportunities have been identified on Dukes Moor within the hotspot. To the north and east of the hotspot, green infrastructure opportunities and strategic green infrastructure opportunities have been identified along the Ouseburn corridor. Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works within the hotspot or local surrounding area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. AECOM Surface Water Management Plan 117
Capabilities on project: Water
Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk. Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic Housing Land resulting from planned growth and identify DAs Availability with the greatest increase in demand resulting Assessments (up to from new development. 2020) and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
The hotspot is located within two Drainage Areas; Gosforth and Jesmond. The results for these two Drainage Areas are detailed in Table 2. The majority of the hotspot is located within the Gosforth Drainage Area, and the overall priority of the Gosforth Drainage Area is 5 (out of 58 total Drainage Areas). The priority ranking of 5 highlights that Northumbrian Water is concerned about the sewerage network in the Gosforth area, and managing this sewer network in the future. Managing surface water within the Gosforth area can therefore be considered an important issue going forward. Table 2: Gosforth and Jesmond Drainage Area Analysis Overall Relative rankings (58 DA considered in Assessment Tyneside study) (without Local weighting) DA Location Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle 05-D31 Gosforth Upon Tyne 4 11 15 29 59 5 City Council
Newcastle 05-D32 Jesmond Upon Tyne 23 12 35 31 101 20 City Council
* Based on data provided 19th November 2010
Newcastle City Council Records of Flooding There are twenty three recorded incidents of historic flooding within the hotspot, which occurred on the; 25th and 29th of August 1999, 27th February 2004, 7th May 2005, 30th June 2005, 14th August 2007, 6th September 2008 and 1st April 2009. The twenty three incidents are dispersed across the hotspot, with the largest cluster of ten incidents in Coxlodge notably around The Meadows and Wansbeck Road South. Two schools in north Gosforth are known to have suffered from flooding in the past; Gosforth High School and Grange First School. Throughout the hotspot, heavy rainfall is known to have caused flooding of properties. There are known drainage problems throughout the hotspot, several of which at the time were caused by localised road gully problems. AECOM Surface Water Management Plan 118
Capabilities on project: Water
Newcastle City Council is currently looking at flood risk and drainage problems associated with Devils Burn upstream of the hotspot, on Nuns Moor. Newcastle City Council commissioned a Feasibility Study in 2004, which identified a number of problems including silt deposition, fly tipping, erosion of burn sides and surface water sewers discharging to the Burn. Newcastle City Council has carried out works, in conjunction with Freemen to clear the watercourse. Newcastle City Council provided a newspaper article on a flood incident that occurred on the 6th August 1978. The newspaper article reports that half an inch of water fell within one hour, causing manhole covers to be forced off drains and roads to flood. The Gosforth district of Newcastle was recorded to be particularly hard hit by flooding, and surface water at Haddrick’s Mill in south Gosforth was recorded to be a foot deep. The newspaper article included a photograph of the flooding in Gosforth in 1978 (right). Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, there appears to be a number of overland flow paths through the hotspot. In the south of the hotspot, there is a pathway along the route of Devils Burn (until the culvert goes under the Metro line). To the north of Devils Burn, there appears to be overland pathways along several sections of Metro line, and one along St James Street and Church Road to the west of the Metro line. Additionally a flow path seems to enter the hotspot in the Jubilee Mews area. In addition to surface water ponding occurring along the overland flow path routes, there are several other areas of significant surface water ponding within the hotspot. In the north east of the hotspot, there is large area of surface water ponding around Hunter’s Road adjacent to the Metro line. To the north of St James Street and Church Road, there is large area of surface water ponding along Spital Terrace, Bath Terrace and Harley Terrace. Other significant pockets of surface water ponding within the hotspot include Warkworth Crescent and the Jubilee Mews area along Jubilee Road. Based on the urban nature of the hotspot, the surface water ponding within the hotspot, and the overland flow pathways through the hotspot, are likely to be a product of rainfall on impermeable areas (buildings, roads etc.) and inadequate drainage capacity during extreme rainfall events. Heavy rainfall is known to have caused numerous flooding incidents within the hotspot. Although runoff from Nuns Moor and Dukes Moor will also affect the flood risk from Devils Burn. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 1294 properties are at risk of flooding within the hotspot. Eleven critical infrastructure locations are also at risk of flooding within the hotspot; three sections of Metro line, two roads (Great North Road (B1318) and Church Avenue (A191)), three stations and three schools. The three schools are risk are Gosforth High School, Newlands Preparatory School and South Gosforth First School and three station at risk are South Gosforth Station, Regent Centre Station (Metro) and Fawdon Station (Metro). Based on the Environment Agency’s Flood Map for Surface Water (deep), there are a number of locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. The areas that could potentially flood to depths greater than 0.3m are generally located along the main overland flow paths though the hotspot, and the main areas of surface water ponding detailed above. Of the eleven critical infrastructure locations at risk of flooding within the hotspot, no stations, roads or schools are predicted to be at risk to depths exceeding 0.3m. Several short sections the Metro line could potentially flood to depths greater than 0.3m. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 119
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing sites. Limited potential Green Roofs for existing residential, commercial and Yes industrial development. Hotspot located within close proximity to the Soakaways/Infiltration Ouseburn. High water table likely to make No infiltration unfeasible. Possibility for housing sites. Also potential to Attenuation/Storage install attenuation storage within available Yes green areas, including Nuns Moor. Often used alongside roads, and potential opportunities along several roads within the Source Source hotspot including Hunters Road, Great North Swales/Filter Drain Yes Road, Church Avenue, Jubilee Road, Spital Terrace, Bath Terrace and Harley Terrace. Further investigation required. Possible for housing sites. Retro fitting also a Permeable Paving possibility, particularly in car parking areas Yes within hotspot. Further investigation required. Overland flows from Nuns Moors and Devils Boundary Flow Interception Yes Burn. Possible for housing sites. Retro fitting also a Rainwater Harvesting Yes possibility. Further investigation required. The overall priority of the Gosforth Drainage Area, which the hotspot is located within, is Increase Sewer Capacity relatively high. Increasing sewer capacity Yes therefore warrants consideration and further investigation required. Combined sewer network within hotspot. Any surface water in combined sewer could Separation of foul/surface water potentially be removed and put into existing Yes systems surface water sewers or new surface water sewers. A number of flood incidents within the hotspot are known to be a result of localised Improve maintenance regime problems associated with drainage gullies. Yes Improved maintenance is therefore key to managing surface water. Potential opportunities for storage along several roads within the hotspot Hunters Flow/Storage on Roadway Road, Great North Road, Church Avenue, Yes Jubilee Road, Spital Terrace, Bath Terrace and Harley Terrace. Flows could potentially be directed to, and managed within the Dukes Moor and other
Pathway Pathway smaller areas of green space available within Manage overland flows the hotspot (playing fields, parks, allotment Yes gardens etc). Flows could also potentially be directed and managed within designated urban areas. Further investigation required. Devils Burn Feasibility Study identified silt deposition, fly tipping and erosion of Devils Improve channel capacity Burn upstream of hotspot. Channel capacity Yes has already been improved in places and work is ongoing elsewhere. Devils Burn is culverted in sections through the hotspot, may be potential to open some Open up culverts Yes of the culverts up. Further Investigation required. Study currently being undertaken to identify Improve floodplain storage Yes potential for storing water on the tributaries of AECOM Surface Water Management Plan 120
Capabilities on project: Water
Technical Mitigation Measure Commentary Feasibility? the Ouseburn. The potential to provide storage on Devils Burn within the hotspot should be investigated further. Devils Burn Feasibility Study identified fly tipping was a problem in Devils Burn. An Remove Obstructions improved maintenance regime within the Yes hotspot could include removing obstructions in Devils Burn. Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even Nationally). Possibility during future development and housing sites within hotspot. However, Planning policies/development planning policies and development control Yes control should be taken forward at a Council wide level for action, as opposed to at individual
Receptor Receptor hotspot level. Possibility during future development, and housing sites within hotspot. Retro fitting also Improve Resilience and resistance Yes possibility and could be targeted at high risk properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 121
Capabilities on project: Water
Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 2 2 1 2 2 125 Yes
Soakaways/Infiltration N/A
Attenuation/Storage 2 2 1 2 1 1 1 170 Yes
Swales/Filter Drain 1 1 0 2 1 2 1 105 Yes Source Source Permeable Paving 1 1 1 0 -1 1 1 75 Maybe
Boundary Flow Interception 2 2 1 2 1 1 1 170 Yes
Rainwater Harvesting 1 -1 1 1 1 2 1 35 Maybe
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 2 0 0 1 1 1 0 65 Maybe water systems Improve maintenance 2 2 1 1 0 0 1 145 Yes regime Flow/Storage on Roadway 1 1 0 1 1 1 1 85 Yes
Manage overland flows 1 2 1 1 -1 1 1 125 Yes Pathway Improve channel capacity 1 2 1 1 -1 1 1 125 Yes
Open up culverts 1 2 1 2 -1 1 2 145 Yes Improve Floodplain 1 2 1 1 -1 1 1 125 Yes Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
The majority of mitigation measures have been identified as being potentially appropriate within this hotspot which is a function of the size of the hotspot and different measures being applicable in different areas. If a more detailed study were undertaken on a small part of the hotspot the number of applicable measures would likely reduce. Based on the size of the hotspot, source and pathway measures have been discussed with reference to specific areas within the hotspot, whereas receptor measures are considered for the hotspot as a whole. Development Sites Four housing sites fall within the hotspot. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The housing sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. The housing sites also appear to be served by combined sewer systems. If this proves to be the case, development ought to remove the surface water from the combined sewers. AECOM Surface Water Management Plan 122
Capabilities on project: Water
Devils Burn (or Crag Hall Dene) Based on the overland flows paths that originate from Nuns Moor and follow Devils Burn, boundary flow interception has been suggested as an appropriate source control mitigation measure. Providing attenuation storage and installing a series of swales within Nuns Moor and Dukes Moor could form the suggested boundary flow interception measures. Newcastle City Council is currently looking at flood risk and drainage problems associated with Devils Burn upstream of the hotspot (on Nuns Moor) to assess how the flood risk could potentially be alleviated. A number of pathway mitigation measures have also been suggested in relation to Devils Burn. The suggested measures include improving channel capacity, opening up the culverted sections and improving floodplain storage along the Burn. Further downstream, within the hotspot there is an open green space between Lodore Road and Rectory Road (photo right). Devils Burn flows under the green space in a culvert therefore there is potential to use the area for storage or even daylighting the watercourse. Potential opportunities may exist to improve channel capacity and provide storage, although further investigation would be required. The watercourse presents both a risk of surface water flooding to residents in its current state, as identified by the Environment Agency’s surface water flood maps, and an opportunity to store water, delaying it getting into the Ouseburn. Newcastle City Council is currently undertaking a study to identify potential for storing water on the tributaries of the Ouseburn, so it is suggested appropriate pathway measures on Devils Burn are considered further as part of this study. Improved maintenance has also been suggested as an appropriate pathway mitigation measure for the hotspot, as there are known problems with Devils Burn (fly tipping, silt deposition, erosion upstream of the hotspot) and drainage gullies throughout the hotspot (localised problems). As part of an improved maintenance regime, it is recommended that Newcastle City Council ensure that all of the culverts and crossings of Devils Burn are entered on their Asset Register of structures capable of posing a flood risk. St James Street and Church Road The housing site in this locality is sited on open green space. Opportunities therefore exist for the City Council to encourage the developer to utilise the open green space to manage surface water holistically for the housing site and the wider area. These streets are presumably a topographic low spot where water would collect, therefore if it could be encouraged to drain into a formal storage area it may alleviate the flood risk in the wider area. This could be in the form of a landscape park or wetland that would have additional biodiversity benefits. Re-grading roads and the provision of kerbing may be required to encourage drainage into the open space. Alternatively if the housing site does not get developed Newcastle City Council to look at potential to utilise the green space for management of surface water, contributing to green infrastructure and providing biodiversity benefits. Spital Terrace, Bath Terrace and Harley Terrace & Warkworth Crescent These residential streets do not have any development opportunities by which to provide flood risk management. As such any mitigation measures would need to be in the form of storing water in the roads, through re-grading and kerbing, or creating formal flow paths to the green spaces that are in close proximity. The presence of residential properties will limit the potential to implement a flow path as it may need to pass through private property. Critical Infrastructure A number of pathway measures are considered potentially appropriate to protect the Metro lines and stations within this hotspot. Managing overland flow and directing it into green spaces or and car parks could hold potential. Northumbrian Water is currently looking into a scheme to divert surface water away from the area of Metro line in the north of the hotspot. Providing storage along roads within the hotspot, particularly those that act as conduits for overland flow, has been identified as appropriate pathway mitigation measure. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development within the hotspot (housing sites). Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development AECOM Surface Water Management Plan 123
Capabilities on project: Water management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH11.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments and the separation of combined flows. NH11.2 – Newcastle City Council to undertake walkover survey of Devils Burn and enter all structures in the Asset Register. NH11.3 – If the SHLAA site on St James Street does not get developed Newcastle City Council to consider using the green space for management of surface water, contributing to green infrastructure and providing biodiversity benefits. NH11.4 – Newcastle City Council to undertake desk top review of potential for Devils Burn/Crag Hall Dene to manage surface water and limit water getting into the Ouseburn. AECOM Surface Water Management Plan 124
Capabilities on project: Water AECOM Surface Water Management Plan 125
Capabilities on project: Wateron project: Water
Hotspot Ref: NH15 Hotspot Location: City Centre – Central and East
Site Description The hotspot is located in Newcastle city centre, and extends from the River Tyne in the south, Town Moor to the north and Hunter’s Moor to the north-west. The hotspot is an urban area of central Newcastle and encompasses the Civic Centre, Newcastle City Hall, and the Universities of Newcastle upon Tyne and Northumbria. There are very few green areas within the hotspot, but Hunter’s Moor and Leazes Park are located immediately to the west of the hotspot and Town Moor to the north. Part of the hotspot has been identified as a green infrastructure opportunity area, and strategic green infrastructure opportunities have also been identified along the River Tyne. Employment and residential opportunities have been identified to the west of the A167 (M) within the hotspot, and the East Pilgrim Street Strategic Site (S10) is suitable for housing development. Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works within the hotspot or local surrounding area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks.
NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk.
Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic resulting from planned growth and identify Housing Land Drainage Areas with the greatest increase in Availability demand resulting from new development. Assessments (up to 2020) and Employment Land Reviews.
Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify Drainage Areas with the greatest number of interactions.
The hotspot is located within the Newcastle City Drainage Area, and the results for this Drainage Area are detailed in Table 2. As Table 2 shows, the overall priority of the Newcastle City Drainage Area is 1 out of 58 Drainage Areas. These priority rankings highlight the stressed nature of the sewerage network in Newcastle City and Benwell, and the importance of AECOM Surface Water Management Plan 126
Capabilities on project: Wateron project: Water managing these sewer networks appropriately in the future. Table 2: Newcastle City Drainage Area Analysis Overall Relative rankings (58 Drainage Area Assessment considered in Tyneside study) (without weighting) Drainage Local Location Area Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle Newcastle Upon Tyne 05-D28 10 9 4 11 34 1 City City Council * Based on data provided 19th November 2010 Newcastle City Council Records of Flooding There are eleven recorded incidents of historic flooding within the hotspot, which occurred on the following dates; 25th August 1999, 3rd July 2004, 30th December 2004, 26th December 2005, 12th June 2006, 4th September 2009 and September 2010. The cause of these surface water flood incidents is not well documented, but they are thought to be associated with heavy rainfall events, a number of overland flow pathways and localised problems with drainage gullies. Areas that are known to have been affected by flooding in the past include the shops at the junction of Pilgrim Street and Worswick Street, areas adjacent to Hunter’s Moor, the Swan House car park (now 55 Degrees North), Great North Road and Eldon Square. Newcastle City Council explained that they have a pump in the underpass at the junction of the A167(M) with New Bridge Street and Durant Road (second interchange north of Tyne Bridge, just to the south of the footbridge linking two sections of Northumbria University). If this pump were to fail during a period of heavy rain, there is the potential for flooding to cause problems. Newcastle City Council provided a photograph of the flooding that occurred on Eldon Square in September 2010, and a photograph of Northumberland Street flooding in 1913. These two photographs follow below.
Photograph 1: Flooding on Eldon Square in 2010 Photograph 2: Flooding on Northumberland Street in 1913
Surface Water Flood Risk Based on the Environment Agency’s Flood Map for Surface Water and Areas Susceptible to Surface Water Flooding, there appears to be several overland flow paths through the hotspot. To the west of the hotspot, an overland flow pathway flows from Nuns Moor onto Ponteland Road (A187) and into the Spital Tongues area of the hotspot. The overland flow pathway then continues through Spital Tongues, along Ancrum Street, and towards the University of Newcastle upon Tyne and the AECOM Surface Water Management Plan 127
Capabilities on project: Wateron project: Water
Civic Centre area along Morpeth Street and Framlington Place. To the north of the hotspot, a second overland flow pathway flows from Town Moor onto Great North Road (B1318) and into the hotspot along this road. The Town Moor and Nuns Moor overland flow pathways converge in the Civic Centre area of the hotspot, where the largest area of surface water ponding occurs within the hotspot (between A176(M) and Barras Bridge (B1307)). To the south of the Civic Centre area, a overland pathway continues along the A167(M). To the east of Civic Centre area, a less significant overland path flows along a railway line (north of Stepney Lane) and appears to cause surface water ponding in the Manors Railway Station area. Based on the urban nature of the hotspot, the surface water ponding within the hotspot, and the overland flow pathways through the hotspot, are likely to be a product of rainfall on impermeable areas (buildings, roads etc.) and extreme rainfall exceeding the capacity of the drainage system. The majority of flood incidents within the hotspot are known to be a result of localised problems associated with drainage gullies. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 447 properties are at risk of flooding within the hotspot. Fourteen critical infrastructure locations are also at risk of flooding within the hotspot; two sections of railway line, eight roads, one infirmary, one university and two stations. The infirmary at risk within the hotspot is the Newcastle Dental Hospital, the two stations at risk are Manors Railway Station and Manors Metro Station and the university at risk is the University of Northumbria. The eight roads considered at risk are Great North Road (B1318), Percy Street/ Barras Bridge (B1307), St Marys Place (B1307), the A167(M), Ponteland Road (A187), John Dobson Street (B1309) and Quayside (B1600). The Newcastle Civic Centre is also at risk and could be considered to be critical infrastructure. Based on the Environment Agency’s Flood Map for Surface Water (deep), there are a number of locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. The areas that could potentially to depths greater than 0.3m are generally located along the main overland flow pathway routes though the hotspot, and in the civic centre area where two overland flow pathways converge. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 128
Capabilities on project: Wateron project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing and employment sites. Green Roofs Yes Limited potential for retro-fittin. Hotspot located adjacent to the River Tyne. Soakaways/Infiltration High water table likely to make infiltration No unfeasible. Possibility for housing and employment sites. Also potential to install attenuation storage Attenuation/Storage Yes within available green areas, including Nuns Moor and Town Moor. Often used alongside roads, and there are Source Source potential opportunities for installation along Swales/Filter Drain several roads within the hotspot including St Yes Marys Place, Barras Bridge and Ancrum Street. Further investigation required. Possible for housing and employment sites. Permeable Paving Yes Retro fitting also a possibility. Boundary Flow Interception Flows from Nuns Moor & Town Moor. Yes Possible for housing and employment sites. Rainwater Harvesting Yes Retro fitting also a possibility. The overall priority of the Newcastle City Drainage Area, which the hotspot is located Increase Sewer Capacity within, is high. Increasing sewer capacity Yes therefore warrants consideration and further investigation required. Combined sewer network within hotspot. Any Separation of foul/surface water surface water in combined sewer could Yes systems potentially be removed or reduced through retro fit measures. The majority of flood incidents within the hotspot are a result of localised problems Improve maintenance regime Yes associated with drainage gullies. Improved maintenance is therefore key. Potential opportunities for storage along
Pathway Pathway several roads within the hotspot including St Flow/Storage on Roadway Yes Marys Place, Barras Bridge and Ancrum Street. Further investigation required. Flows could potentially be directed to, and Manage overland flows managed within the adjacent Moor and Yes Parkland areas or the River Tyne. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Yes sewer network Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally. Possibility during future development, and housing and employment sites within Planning policies/development hotspot. However, planning policies and Yes control development control should be taken forward at a Council wide level for action, as opposed to at individual hotspot level. Receptor Receptor Possibility during future development, and housing and employment sites within Improve Resilience and resistance hotspot. Retro fitting also possibility and Yes could be targeted at high risk properties (i.e. deep flooding). AECOM Surface Water Management Plan 129
Capabilities on project: Wateron project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 1 2 1 2 1 105 Yes
Soakaways/Infiltration N/A
Attenuation/Storage 2 2 1 2 1 1 1 170 Yes
Swales/Filter Drain 1 1 0 2 1 2 1 105 Yes Source Source Permeable Paving 2 1 1 0 -1 1 1 95 Yes
Boundary Flow Interception 2 2 1 2 1 1 1 170 Yes
Rainwater Harvesting 2 0 1 1 1 2 1 90 Yes
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 2 -1 1 1 -2 1 1 35 Maybe water systems Improve maintenance 2 2 1 1 0 0 1 145 Yes regime Flow/Storage on Roadway 1 1 0 1 1 1 1 85 Yes
Manage overland flows 1 2 1 1 -1 1 1 125 Yes
Pathway Improve channel capacity N/A
Open up culverts N/A Improve Floodplain N/A Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance AECOM Surface Water Management Plan 130
Capabilities on project: Wateron project: Water
Development Sites Housing and employment sites fall within the hotspot. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where combined sewers exist, development ought to remove surface water from the combined system. Hunters Moor and Town Moor A number of source control mitigation measures have been identified as potentially appropriate within this hotspot. Based on the overland flows paths that originate from Hunters Moor and Town Moor, boundary flow interception has been suggested as an appropriate source control mitigation measure. Providing attenuation storage and installing a series of swales within Hunters Moor and Town Moor could form of the suggested boundary flow interception measures. Pathway Measures Managing overland flow and directing flows to the adjacent Moor and Parkland areas, into the River Tyne and potentially areas within the hotspot such as small green spaces or car parks has been identified as appropriate mitigation measures. Providing storage along roads within the hotspot, particularly those that act as conduits for overland flow, has also been identified as appropriate pathway mitigation measure. This is applicable throughout the urban area of the hotspot. Improved maintenance has been suggested as an appropriate pathway mitigation measure for the hotspot, and as the majority of flood incidents within the hotspot are a result of problems with highway drainage networks. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific. In terms of mitigation measures, it should be highlighted that at business continuity plan is currently being looked at for the Civic Centre that is located in topographic low spot and at risk of flooding.
Recommendations NH15.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH15.2 – As part of highway improvement or maintenance works, explore the potential for storing water in roads or channelling it overland into the River Tyne. AECOM Surface Water Management Plan 131
Capabilities on project: Water AECOM Surface Water Management Plan 132
Capabilities on project: Water
Hotspot Ref: NH16 Hotspot Location: City Centre – West
Site Description The hotspot is located in Newcastle city centre, adjacent to Central Station, St James Park and the River Tyne. The hotspot is an urban area with limited green space. Grey Street, located to the south of Monument Mall, used to be an open watercourse that and was culverted and filled in Georgian times to facilitate development. The hotspot has been identified as a green infrastructure opportunity area given its proximity to the River Tyne. Housing and employment development opportunities have been identified to south the Strawberry Place, adjacent to St James Park and two small sites to the south east of Newcastle Market. Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works within the hotspot or local surrounding area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks.
NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk.
Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic resulting from planned growth and identify Housing Land Drainage Areas with the greatest increase in Availability demand resulting from new development. Assessments (up to 2020) and Employment Land Reviews.
Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify Drainage Areas with the greatest number of interactions.
The hotspot is located within two Drainage Areas; Newcastle City and Benwell. The results for these Drainage Areas are detailed in Table 2. The majority of the hotspot is located within the Newcastle City Drainage Area. As Table 2 shows, the overall priority of the Newcastle City and Benwell Drainage Areas are 1 and 2 respectively (out of 58 total Drainage Areas). These priority rankings highlight the stressed nature of the sewerage network in Newcastle City and Benwell, and the importance of managing these sewer networks appropriately in the future. AECOM Surface Water Management Plan 133
Capabilities on project: Water
Table 2: Newcastle City and Benwell Drainage Area Analysis Overall Relative rankings (58 Drainage Area Assessment considered in Tyneside study) (without weighting) Drainage Local Location Area Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle Newcastle Upon Tyne 05-D28 10 9 4 11 34 1 City City Council Newcastle Upon Tyne 05-D27 Benwell 1 18 5 15 39 2 City Council * Based on data provided 19th November 2010 Newcastle City Council Records of Flooding There are sixteen recorded incidents of historic flooding within the hotspot. Eight of these recorded flood incidents occurred along Sandhill and Queen Street, to the south of the railway line and adjacent to the River Tyne. Flooding was recorded along these two roads on the 26th September 1999, 22nd August 2005, 12th September 2000, 14th June 2001 and on the 23rd June 2007. The cause of these flooding incidents can be attributed to a blocked sewer, a burst water pipe, interaction between a surge tide and the sewer system and heavy rainfall. To the north of the railway line and to the south Gallowgate (B1311), there are five recorded incidents within the hotspot. Dean Street (adjacent to St Nicolas Cathedral) is recorded to have on the 23rd June 2007 as a result of a sewer issuing. Blackett Street is recorded to have flooded on the 7th September 2008, although the cause of this flooding incident is unknown. The basement and service yard of the Co-operative Building are recorded to have flooded on the 19th of August 2002. The cause of flooding was concrete in the private drain connection, the connection has now been renewed. There are two recorded incidents of Grey Street flooding, although the cause and dates of the two flooding incidents are unknown. There are three recorded incidents of Gallowgate (B1311) (adjacent to St James Park) flooding; 2000, 2003 and 2009. On the 12th of August 2000, Gallowgate is recorded to have flooded as a result of blocked pipes. The cause and exact dates of the 2003 and 2009 flooding incidents on Gallowgate are unknown. Although the causes of the 2000, 2003 and 2009 flood incidents on Gallowgate are unknown, surface water is known to run down Barrack Road and cause flooding on Gallowgate and St Andrews Street. The former Co-operative building in the Gallowgate and St Andrews Street area is known to regularly flood. The area around the Co-operative building is most recently known to have flooded in 2010, and Newcastle City Council provided a photograph of this flooding. Newcastle City Council has provided advice on resistance and resilience measures for this building. The majority of flood incidents within the hotspot are known to be a result of localised problems with gullies. During extreme rainfall events there is evidence of sewer surcharging, Newcastle City Council are working with Northumbrian Water to manage this issue. In 2010, flooding is known to have occurred along Newgate Street and the Quayside (B1600). Newcastle City Council provided photographs of these flooding incidents, and these photographs follow below. The cause of these flooding incidents was an extreme rainfall event which exceeded the capacity of road gullies and drainage networks. Newcastle City Council also provided a photograph of Diana Street flooding in 2010, which is located to the west of the hotspot. AECOM Surface Water Management Plan 134
Capabilities on project: Water
Photograph 3: Historic Flooding along Newgate Photograph 4: Historic Flooding along Newgate Street in 2010 Street in 2010
Photograph 5: Historic Flooding along Quayside in 2010
Photograph 6: Historic Flooding along Quayside in Photograph 7: Historic Flooding along Diana Street in 2010 2010 AECOM Surface Water Management Plan 135
Capabilities on project: Water
Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, there appears to be several overland flow pathways through the hotspot. These flow paths appear to flow along several roads within the hotspot, with surface water ponding occurring in two main locations. Overland flows are likely to enter the hotspot via Barrack Road (which could be receiving runoff from Leazes Park and via Westgate Road (A186). Overland flow appears to flow along Westgate Road (A186), Grey Street and Sandhill/ Quayside (B1600), with the two main pockets of surface water ponding occurring adjacent to Westgate Road and in the Newgate Street and Clayton Street area (to the west of the Market). As previously detailed, this hotpot is located within central Newcastle. The surface water ponding within the hotspot, and the overland flow pathways through the hotspot, are likely to be a product of rainfall on impermeable areas (buildings, roads etc.) and inadequate drainage. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 178 properties are at risk of flooding within the hotspot. Five critical infrastructure locations are also at of flooding within the hotspot; one section of railway line, Westgate Road (A186), Dean Street (B1600), Gallowgate (B1311), Sandhill/ Quayside (B1600) and St James Metro Station. The properties identified as being at risk of flooding are primarily located in the two main pockets of surface water ponding within the hotspot; adjacent to Westgate Road and in the Newgate Street and Clayton Street area. The remaining properties at risk are generally located adjacent to roads acting as conduits for overland flow. Based on the Environment Agency’s Flood Map for Surface Water (deep), there are five locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. These five areas are located adjacent to the following roads; Westgate Road, Pudding Chare, Stowell Street, Clayton Street area and Gallowgate. The roads themselves are predicted to be at risk from flood depths exceeding 0.3m during a 1 in 200 year flood event, and the only critical infrastructure location at risk of flooding from flood depths exceeding 0.3 is to St James Metro Station. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 136
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing and employment sites. Green Roofs Limited potential for existing development. Yes Hotspot located adjacent to the River Tyne. Soakaways/Infiltration Water table likely to make infiltration No unfeasible. Possibility for housing and employment sites. Attenuation/Storage Yes Also potential to retrofit (i.e car parks). Often used alongside roads, potential Source Source Swales/Filter Drain opportunities along; Westgate Road, Dean Yes Street, Gallowgate, and Sandhill/Quayside. Possible for housing and employment sites. Permeable Paving Retro-fitting possible e.g. car parking areas. Yes
Boundary Flow Interception N/A No Possible for housing and employment sites. Rainwater Harvesting Yes Retro fitting also a possibility. Sewer capacity is known to be problem in the Benwell Drainage Area, which part of the hotspot site is located within. The overall Increase Sewer Capacity Yes priority is high. Increasing sewer capacity therefore warrants consideration. Further investigation required. Combined sewer network within hotspot. Separation of foul/surface water New development should endeavour to Yes systems remove surface water from the combined sewer. The majority of flood incidents within the hotspot are a result of localised problems Improve maintenance regime Yes associated with drainage gullies. Improved maintenance is therefore key. Potential opportunities for storage along
Pathway several roads within the hotspot; Westgate Flow/Storage on Roadway Yes Road, Dean Street, Gallowgate, and Sandhill/ Quayside. Flows could potentially be directed to, and managed within green, open urban areas Manage overland flows Yes within the hotspot (i.e car parks) or the River Tyne. Further investigation required. Improve channel capacity N/A No Grey Street used to be a burn, and was Open up culverts culverted and filled in Georgian times. Limited Limited potential to open this culvert up. Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Yes sewer network Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally. Possibility during future development, and housing and employment sites within Planning policies/development hotspot. However, planning policies and Yes control development control should be taken forward at a Council wide level for action, as opposed to at individual hotspot level. Receptor Receptor Possibility during future development, and housing and employment sites within Improve Resilience and resistance hotspot. Retro fitting also possibility and Yes could be targeted at high risk properties (i.e. deep flooding). AECOM Surface Water Management Plan 137
Capabilities on project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 1 1 1 1 1 85 Yes
Soakaways/Infiltration N/A
Attenuation/Storage 2 2 1 2 1 1 1 170 Yes
Swales/Filter Drain 1 1 0 2 1 2 1 105 Yes Source Source Permeable Paving 2 1 1 0 -1 1 1 95 Yes
Boundary Flow Interception N/A
Rainwater Harvesting 2 0 1 1 0 1 1 80 Yes
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 2 0 1 1 -1 1 1 75 Maybe water systems Improve maintenance 2 2 1 1 0 0 1 145 Yes regime Flow/Storage on Roadway 1 1 0 1 1 1 1 85 Yes
Manage overland flows 1 2 1 1 -1 1 1 125 Yes
Pathway Improve channel capacity N/A
Open up culverts -2 -2 -2 2 -2 2 2 -100 No Improve Floodplain N/A Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Sites Housing and employment sites fall within the hotspot. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where AECOM Surface Water Management Plan 138
Capabilities on project: Water combined sewers exist, development ought to remove surface water from the combined system. Retro-fitting Retro-fitting attenuation storage and permeable paving within the existing urban areas such as car parks has also been suggested as a potential mitigation measure, based on the limited of green space available within the hotspot. Providing storage along a number of the roads within the hotspot has been identified as appropriate mitigation measure, as has using the roads to manage overland flows. As appropriate, attenuation storage could be installed along roads and within existing car parking areas to provide formal flood storage. Based on the proximity of the hotspot to the River Tyne, it is likely the most preferable means of managing flows would be to channel them directly into the river. Improved maintenance has been suggested as an appropriate pathway mitigation measure for the hotspot, and as the majority of flood incidents within the hotspot are a result of problems with highway drainage. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development within the hotspot (housing and employment site). Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH16.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH16.2 – As part of highways improvement or maintenance work, explore the potential for storing water in roads or channelling it overland into the River Tyne. AECOM Surface Water Management Plan 139
Capabilities on project: Water AECOM Surface Water Management Plan 140
Capabilities on project: Water
Hotspot Ref: NH19 Hotspot Location: Walkergate
Site Description The hotspot is located in Walkergate in the east of Newcastle with a railway line running through the centre of the hotspot. The hotspot encompasses residential, commercial and industrial areas to the east and west of the railway line. The only green space within the hotspot is a playing field to the west of the railway line. This playing field is known to have to tanked storage underneath the surface, to accommodate sewer overflows. Within the hotspot, a site has been identified as suitable for housing development (Walkergate business park area) to the east of the railway line and a second housing site exists immediately to the south west of the hotspot at Heaton Junction. Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works within the hotspot or local surrounding area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks.
NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk.
Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic resulting from planned growth and identify Housing Land Drainage Areas with the greatest increase in Availability demand resulting from new development. Assessments (up to 2020) and Employment Land Reviews.
Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify Drainage Areas with the greatest number of interactions.
The hotspot is located within the Heaton Drainage Area, and the results for this Drainage Area are detailed in Table 2. As Table 2 shows, the overall priority of the Walker Drainage Area is 50 out of 58 Drainage Areas. The relative ranking of the Heaton Drainage Area is only in the top thirty priority Drainage Areas of capacity map ranking and growth data ranking, with a ranking of 24 and 28 out of 58 respectively. The overall priority of the Walker Drainage Area can therefore be considered low. AECOM Surface Water Management Plan 141
Capabilities on project: Water
Table 2: Heaton Drainage Area Analysis Overall Relative rankings (58 Drainage Area Assessment considered in Tyneside study) (without weighting) Drainage Local Location Area Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle Upon Tyne 05-D36 Heaton 24 54 28 49 155 50 City Council * Based on data provided 19th November 2010 Newcastle City Council Records of Flooding There are four known incidents of historic flooding within the hotspot; on Benfield Road, Rothbury Terrace, Sackville Road and Jasmine Close. The most recent flooding incident on Benfield Road occurred in 2005, when the stretch of road under the Metro bridge, Benfield Road between the school and Jasmine Close and Jasmine Close flooded. Prior to the 2005 flood event, the road under the Metro Bridge was known to flood regularly. Based on the regular flooding experienced along Benfield Road, the drainage gullies along the road were replaced in 2006/7. There are no records of Benfield Road flooding since the drainage gullies were replaced. There is no information available on the flooding incidents on Rothbury Terrace, Sackville Road and Jasmine Close. However, it is known that the drainage gullies on Jasmine Close were cleaned as a result of requests received from residents. Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, the railway embankment appears to act as a barrier to overland flow and surface water ponding occurs along the length of the railway embankment. A surface water sewer runs along the edge of the western railway embankment, which could potentially also contribute to ponding in this location. To the east of the railway line, there appears to be an overland flow path and flows adjacent to Benfield Road. A combined sewer runs along Benfield Road. There does not appear to be any significant overland flow entering the hotspot from outside the hotspot boundary. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 238 properties are at risk of flooding within the hotspot. The properties at risk of flooding are primarily located in two areas; between Rothbury Terrace and Marleen Avenue to the west of the railway line that bisects the hotspot and in the Benfield Road and Jasmine Close areas to the east of the railway line. The only properties at risk of flooding along the length of the railway embankment (where ponding occurs) are several railway depot buildings. Three critical infrastructure locations are also at risk of flooding within the hotspot; two sections of railway line and Walkergate Hospital. Based on the Environment Agency’s Flood Map for Surface Water (deep), there are several locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. A number of properties on Marleen Avenue and Jasmine Close are at risk of flooding to depths greater than 0.3m a 1 in 200 year flood event. The critical infrastructure at of flooding in the hotspot (two sections of railway line and Walkergate Hospital) are not considered to be at risk from flood depths exceeding 0.3m during a 1 in 200 year flood event. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within AECOM Surface Water Management Plan 142
Capabilities on project: Water the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing sites. Retro-fitting not Green Roofs Yes considered appropriate. Hotspot located within 1.5km of the River Soakaways/Infiltration Tyne. Groundwater levels are likely to make No infiltration unfeasible. Possibility for housing sites. Limited space available to install in existing residential Attenuation/Storage housing areas. Potential to install additional Yes attenuation storage on playing field (storage tank already installed under playing field).
Source Source Often used alongside roads, potential opportunities along Benfield Road. Swales Swales/Filter Drain could also be installed in playing field to the Yes west of railway to convey and store water (storage tank already under playing field). Possible for housing sites. Retro fitting also a Permeable Paving Yes possibility. Boundary Flow Interception N/A No Possible for housing sites. Retro fitting also a Rainwater Harvesting Yes possibility. Further investigation required.
Increase Sewer Capacity Yes
Combined and separate sewers run though Separation of foul/surface water hotspot. Any surface water in combined Yes systems sewer could potentially be removed and put into surface water sewer network. Although there are no known drainage Improve maintenance regime Yes problems. Pathway Potential opportunities for storage along Flow/Storage on Roadway Yes Benfield Road. Flows could potentially be directed to, and managed within the playing field to the west Manage overland flows of the railway line and the Benfield School Yes playing fields to the east of the railway line. Further investigation required. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Yes sewer network Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally). Possibility during future development, and housing site within hotspot. However, Planning policies/development planning policies and development control Yes control should be taken forward at a Council wide level for action, as opposed to at individual
Receptor Receptor hotspot level. Possibility during future development, and housing site within hotspot. Retro fitting also Improve Resilience and resistance Yes possibility and could be targeted at high risk properties (i.e. deep flooding). AECOM Surface Water Management Plan 143
Capabilities on project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 1 2 1 2 1 105 Yes
Soakaways/Infiltration NA
Attenuation/Storage 2 2 1 2 1 1 1 170 Yes
Swales/Filter Drain 1 1 0 2 1 2 1 105 Yes Source Source Permeable Paving 2 1 0 0 -1 1 1 80 Yes
Boundary Flow Interception NA
Rainwater Harvesting 2 0 1 1 1 2 1 90 Yes
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 2 -1 1 1 -2 1 1 35 Maybe water systems Improve maintenance 2 2 1 1 0 0 1 145 Yes regime Flow/Storage on Roadway 1 1 0 1 1 1 1 85 Yes
Manage overland flows 1 2 1 1 -1 1 1 125 Yes
Pathway Improve channel capacity NA
Open up culverts NA Improve Floodplain NA Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Sites Housing sites fall within and next to the hotspot. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where combined sewers exist, development ought to remove surface water from the combined system. AECOM Surface Water Management Plan 144
Capabilities on project: Water
Playing Field Areas A number of source control mitigation measures have been identified as potentially appropriate, based on the playing field area available within the hotspot, providing additional attenuation storage and installing a series of swales within the playing field has been suggested as an appropriate source control mitigation measure. A storage tank has already been installed under playing field. In addition to source control mitigation measures, a number of pathway measures are considered potentially appropriate within this hotspot. Managing overland flow and directing flow to the locally available green areas within the hotspot (playing field to west of railway line and Benfield School playing fields to east of railway line) have been identified as appropriate mitigation measures. Formal flood storage could be provided within these playing fields. Providing storage along Benfield Road has also been identified as an appropriate mitigation measure within the hotspot. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development within the hotspot (housing site). Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH19.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH19.2 – As part of highways improvement or maintenance works, explore the potential for storing water in roads or channelling it overland into formal storage areas that could be in the playing fields to the east and west of the railway line. AECOM Surface Water Management Plan 145
Capabilities on project: Water AECOM Surface Water Management Plan 146
Capabilities on project: Water
Hotspot Ref: NH23 Hotspot Location: Walker North
Site Description The hotspot is located in Walker in the east of Newcastle, adjacent to the River Tyne. The hotspot encompasses residential, commercial and industrial areas, a large area green open space (to the south of Foss Way (A187)) and commercial facilities adjacent to the River Tyne. A culverted watercourse is thought to have once flowed through the green area to the south of Foss Way in the past, which has now been incorporated into the sewer network. Within the hotspot, employment, green infrastructure and strategic green infrastructure development opportunities have been identified adjacent to the River Tyne. Residential development opportunities have been identified along Foss Way (A187). Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works within the hotspot or local surrounding area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks. NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk. Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic Housing Land resulting from planned growth and identify Availability Drainage Areas with the greatest increase in Assessments (up to demand resulting from new development. 2020) and Employment Land Reviews. Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify Drainage Areas with the greatest number of interactions.
The hotspot is located within the Walker Drainage Area, and the results for this Drainage Area are detailed in Table 2. As Table 2 shows, the overall priority of the Walker Drainage Area is 9 out of 58 Drainage Areas. In addition to this relatively high priority it should be highlighted that the relative ranking of the Walker Drainage Area is 1 out of 58 for the influence of rivers, which identifies that the Walker Drainage Area greatest number of interactions between high risk fluvial flooding locations and discharges from the public sewerage system of all 58 Drainage Areas considered in the study. AECOM Surface Water Management Plan 147
Capabilities on project: Water
Table 2: Walker Drainage Area Analysis Overall Relative rankings (58 Drainage Area Assessment considered in Tyneside study) (without weighting) Drainage Local Location Area Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle Upon Tyne 05-D35 Walker 30 17 25 1 73 9 City Council * Based on data provided 19th November 2010 Newcastle City Council Records of Flooding There are six incidents within the hotspot. Four of these incidents occurred in the Dry Dock area (adjacent to the River Tyne). The date and cause of these incidents is not recorded. The two other recorded incidents within the hotspot occurred on Ashbourne Avenue and Scrogg Road. Scrogg Road flooded on the 19th June 2005 as a result of inadequate drainage. The date and cause of the flooding incident on Ashbourne Avenue is unknown. In 2010, flooding is known to have occurred along Waverdale Avenue (A186). Newcastle City Council provided photographs of the flooding that occurred along Waverdale Avenue in 2010, one of which is reproduced to the left. The cause and exact date of this flooding incident is unknown. Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, there appears to be several overland flow pathways through the hotspot. These flow paths appear to flow through the hotspot from west to east, roughly following the existing sewer network route, towards the River Tyne. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 309 properties are at risk of flooding within the hotspot. The 309 properties at risk of flooding are primarily located within the western half of the hotspot; west of Scrogg Road, the northern ends of Baret Road and Whinneyfield Road and along Kentmere Avenue, Borrowdale Avenue and Corby Gardens. One critical infrastructure location is also at risk of flooding within the hotspot; Waverdale Avenue (A186). Based on the Environment Agency’s Flood Map for Surface Water (deep), there are several locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. All the residential areas area identified as being at risk of flooding could flood to depths exceeding 0.3m, and the Waverdale Avenue could also potentially flood to depths greater than 0.3m. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 148
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing and employment sites. Green Roofs Not considered appropriate for existing Yes development. Hotspot located adjacent to the River Tyne. Soakaways/Infiltration High water table likely to make infiltration No unfeasible. Possibility for housing and employment sites. Attenuation/Storage Also potential to install attenuation storage Yes within green, open space within hotspot. Often used alongside roads, and there are Source Source potential opportunities for installation along Swales/Filter Drain Waverdale Avenue. Swales could also be Yes installed with the green, open space areas to convey and store water. Possible for housing and employment sites. Permeable Paving Yes Retro fitting also a possibility. Boundary Flow Interception N/A No Possible for housing and employment sites. Rainwater Harvesting Yes Retro fitting also a possibility. Sewer capacity is not known to be problem in Increase Sewer Capacity the area, but increasing sewer capacity could Yes be targeted to problem areas. Combined sewer and separate surface water Separation of foul/surface water sewer run though hotspot. Any surface water Yes systems in combined sewer could potentially be removed and put into surface water sewer. Although there are no known drainage problems, maintenance is key to facilitating Improve maintenance regime Yes future development (housing and employment site).
Potential opportunities for storage along Pathway Flow/Storage on Roadway Waverdale Avenue. Further investigation Yes required. Flows could potentially be directed to, and Manage overland flows managed within green, open space areas or Yes to the River Tyne. Improve channel capacity N/A No Culverted watercourse has been Open up culverts incorporated into sewer network, so not No considered a feasible option. Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Yes sewer network Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally. Possibility during future development, and housing and employment sites within Planning policies/development hotspot. However, planning policies and Yes control development control should be taken forward at a Council wide level for action, as opposed to at individual hotspot level. Receptor Receptor Possibility during future development, and Housing and employment sites within Improve Resilience and resistance hotspot. Retro fitting also possibility and Yes could be targeted at high risk properties (i.e. deep flooding). AECOM Surface Water Management Plan 149
Capabilities on project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 1 1 1 1 1 85 Yes
Soakaways/Infiltration N/A
Attenuation/Storage 2 2 1 2 1 1 1 170 Yes
Swales/Filter Drain 1 1 0 2 1 2 1 105 Yes Source Source Permeable Paving 2 1 0 0 0 1 1 85 Yes
Boundary Flow Interception N/A
Rainwater Harvesting 2 0 1 1 1 2 1 90 Yes
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 2 -1 1 1 -2 1 2 40 Maybe water systems Improve mainteN/Ance 2 2 1 1 0 0 1 145 Yes regime Flow/Storage on Roadway 1 1 0 1 1 1 1 85 Yes
Manage overland flows 1 2 1 1 -1 1 1 125 Yes
Pathway Improve channel capacity N/A
Open up culverts N/A Improve Floodplain N/A Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Sites Housing and employment sites fall within the hotspot. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The development sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. Where combined sewers exist, development ought to remove surface water from the combined system. AECOM Surface Water Management Plan 150
Capabilities on project: Water
Whinneyfield Road and Kentmere Avenue A number of source control mitigation measures have been identified as potentially appropriate within this hotspot. Based on the green open space available within the hotspot, providing attenuation storage and installing a series of swales within the park and the open space between Whinneyfield Road and Kentmere Avenue has been suggested as an appropriate source control mitigation measure. Ennerdale Road and Waverdale Avenue In addition to source control mitigation measures, a number of pathway measures are considered potentially appropriate within this hotspot. Managing overland flow and directing flow to the River Tyne and the green areas within the hotspot have been identified as appropriate mitigation measure. Ennerdale Road could provide means of directing flows to the entrance to the park opposite Eastbourne Avenue and Waverdale Avenue could also be modified to allow water to drain into the open green space. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development within the hotspot (housing and employment sites). Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH23.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH23.2 – As part of highways improvement or maintenance works, explore the potential for storing water in roads or channelling it overland into formal storage areas that could be in the park. AECOM Surface Water Management Plan 151
Capabilities on project: Water AECOM Surface Water Management Plan 152
Capabilities on project: Water
Hotspot Ref: NH24 Hotspot Location: Walker Central
Site Description The hotspot is located in Walker to the east of Newcastle, approximately 500m to the west of the River Tyne. The hotspot encompasses Walker Park and surrounding areas of residential and commercial development. The hotspot has been identified as a green infrastructure opportunity area given its proximity to the River Tyne, and part of the site has also been identified as suitable for housing development (adjacent to Titan Road). Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works within the hotspot or local surrounding area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks.
NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk.
Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic resulting from planned growth and identify Housing Land Drainage Areas with the greatest increase in Availability demand resulting from new development. Assessments (up to 2020) and Employment Land Reviews.
Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify Drainage Areas with the greatest number of interactions.
The hotspot is located within the Walker Drainage Area, and the results for this Drainage Area are detailed in Table 2 which shows that the overall priority of the Walker Drainage Area is 9 out of 58 Drainage Areas which is relatively high. It should also be highlighted that the relative ranking of the Walker Drainage Area is 1 out of 58 for the influence of rivers, which identifies that the Walker Drainage Area greatest number of interactions between high risk fluvial flooding locations and discharges from the public sewerage system of all 58 Drainage Areas considered in the study. AECOM Surface Water Management Plan 153
Capabilities on project: Water
Table 2: Walker Drainage Area Analysis Overall Relative rankings (58 Drainage Area Assessment considered in Tyneside study) (without weighting) Drainage Local Location Area Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle Upon Tyne 05-D35 Walker 30 17 25 1 73 9 City Council * Based on data provided 19th November 2010 Newcastle City Council Records of Flooding There are two recorded incidents of historic flooding within the hotspot. On the 27th December 2005 a property on Duncan Street flooded and on the 15th February 2008 a property off Titan Road flooded. The cause of these flooding incidents is unknown. Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, there is one main area of surface water ponding within the hotspot which falls within Walker Park. The main area of surface water ponding within the hotspot appears to correspond with a low spot, based in the Ordnance Survey maps. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 83 properties are at risk of flooding within the hotspot. The properties identified as being at risk of flooding are primarily located between Titan Road and Walker Park. No critical infrastructure is at risk of flooding within the hotspot. Based on the Environment Agency’s Flood Map for Surface Water (deep), there are four locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. Two of these locations are within Walker Park, no properties are affected. The other two locations are residential areas on Hexham Avenue and Titan Road. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 154
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing site. Not considered Green Roofs Yes appropriate for existing development. Hotspot located within 500m of the River Soakaways/Infiltration Tyne. High water table likely to make No infiltration unfeasible. Possibility for housing site and within Walker Attenuation/Storage Yes Park. Often used alongside roads, potential
Source Source opportunities for installation along Duncan Swales/Filter Drain Yes Street. Swales could also be installed with Walker Park to convey and store water. Possible for housing site hotspot. Retro fitting Permeable Paving Yes also a possibility. Boundary Flow Interception N/A No Possible for housing site. Retro fitting also a Rainwater Harvesting Yes possibility. Sewer capacity is not known to be problem in the area, but increasing sewer capacity could Increase Sewer Capacity be targeted to problem areas. Sewer on Yes North Avenue, just outside hotspot, being replaced by Northumbrian Water. Separation of foul/surface water Separate foul and surface water systems No systems already exist. Although there are no known drainage Improve maintenance regime problems, maintenance is key to facilitating Yes
future development. Potential opportunities for storage along
Pathway Flow/Storage on Roadway Yes Duncan Street. Flows could potentially be directed to, and Manage overland flows Yes managed within Walker Park. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Yes sewer network Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally). Possibility during future development, and housing site within hotspot. However, Planning policies/development planning policies and development control Yes control should be taken forward at a Council wide level for action, as opposed to at individual
Receptor Receptor hotspot level. Possibility during future development, and housing site within hotspot. Retro fitting also Improve Resilience and resistance Yes possibility and could be targeted at high risk properties (i.e. deep flooding).
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. AECOM Surface Water Management Plan 155
Capabilities on project: Water
Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
2 0 2 2 1 2 2 125 Yes Green Roofs NA Soakaways/Infiltration 2 2 1 2 1 1 1 170 Yes Attenuation/Storage 1 1 0 2 1 2 1 105 Yes Swales/Filter Drain Source Source 2 1 0 1 -1 1 1 95 Yes Permeable Paving NA Boundary Flow Interception
Rainwater Harvesting 2 0 1 1 1 2 1 90 Yes -1 -2 0 0 -1 1 -1 -95 No Increase Sewer Capacity Separation of foul/surface NA water systems Improve maintenance 2 2 1 1 0 0 1 145 Yes regime 1 1 0 1 1 1 1 85 Yes Flow/Storage on Roadway Yes Manage overland flows 1 2 1 1 -1 1 1 125
Pathway NA Improve channel capacity NA Open up culverts Improve Floodplain NA Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Sites A large housing site falls within the hotspot and a number of others in close proximity. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The housing sites present opportunities to manage surface water on site through green roofs, storage, swales, permeable paving and rainwater harvesting. These measures would have the benefits of contributing to the green infrastructure network in the area and link to additional storage to be provided within Walker Park. Walker Park Based on the green, open space available within Walker Park providing attenuation storage and installing a series of swales within the park has been suggested as an appropriate source control mitigation measure. The park also provides the opportunity for attenuation storage if the housing site were to be developed. It may be that the developer could work with AECOM Surface Water Management Plan 156
Capabilities on project: Water
Newcastle City Council to develop formal storage areas within the park which could also bring about biodiversity benefits. There are a number of other housing sites in close proximity and it is recommended that a surface water management strategy is holistically developed to cover the whole area so that all of the sites utilise Walker Park for storage or excess surface water or a flow path to the River Tyne is created that all sites could tie into. In addition to source control mitigation measures, a number of pathway measures are considered potentially appropriate within this hotspot. Managing overland flows, to direct and manage flow within Walker Park, has been identified as an appropriate mitigation measure. Providing storage along Duncan Street has also been identified as appropriate mitigation measure within the hotspot. In addition to managing overland flows, implementing an improved maintenance regime within the hotspot should also be considered. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH24.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH24.2 – Partners to work with developers of SHLAA sites to utilise Walker Park as a formal means of managing excess surface water runoff.
AECOM Surface Water Management Plan 157
Capabilities on project: Water AECOM Surface Water Management Plan 158
Capabilities on project: Water
Hotspot Ref: NH35 Hotspot Location: Westerhope
Site Description Hotspot NH35 primarily covers a residential area of Westerhope, which is located on Stamfordham Road (B6324). There is also a large area of commercial development within the hotspot, located to the west of Newbiggin Lane. Westerhope golf course is located immediately to the west of this commercial area, and has been identified as being potentially suitable for development in the Council’s Strategic Land Review assessment. Northumbrian Water Capital Works Immediately to the south of the hotspot, the combined sewer that runs along North Avenue is known to suffer from incapacity problems and Northumbrian Water is planning to replace the sewer. Construction is due to start in November/ December 2011, with a completion date of March 2012. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at Drainage Area level and identify those areas with the greatest capacity risks.
NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. Drainage Area to cope with rainfall events and identify Drainage Areas with the greatest hydraulic risk.
Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic resulting from planned growth and identify Housing Land Drainage Areas with the greatest increase in Availability demand resulting from new development. Assessments (up to 2020) and Employment Land Reviews.
Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify Drainage Areas with the greatest number of interactions.
The hotspot is located within the Denton Valley Drainage Area, and the results for this Drainage Area are detailed in Table 2. As Table 2 shows, the overall priority of the Denton Valley Drainage Area is 28 out of 58 Drainage Areas. It should be highlighted that the relative ranking of the Denton Valley Drainage Area is 2 out of 58 for the Northumbrian Water Capacity Map, which identifies that the Denton Valley Drainage Area has the second greatest capacity risks of the 58 Drainage Areas considered in the study. AECOM Surface Water Management Plan 159
Capabilities on project: Water
Table 2: Denton Valley Drainage Area Analysis Overall Relative rankings (58 Drainage Area Assessment considered in Tyneside study) (without weighting) Drainage Local Location Area Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon) Newcastle Denton Upon Tyne 05-D26 2 45 27 42 116 28 Valley City Council * Based on data provided 19th November 2010 Newcastle City Council Records of Flooding There are three recorded incidents of historic flooding within the hotspot, which occurred in 1941, 1999 and 2008. In 1941, flooding is recorded to have occurred in Chatsworth Gardens and Buxton Gardens. Newcastle City Council provided photographs of the flooding that occurred along these two streets in 1941, and these photographs follow below. The cause and exact date of these flooding incidents is unknown, although it is interesting to note that the hotspot and consequently the flooding is located on top of a hill. Photograph 8: Historic Flooding along Chatsworth Gardens in 1941
Photograph 9: Historic Flooding along Buxton Gardens in 1941 AECOM Surface Water Management Plan 160
Capabilities on project: Water
On the 26th July 1999, Orion Bingo on Stamfordham Road is recorded to have flooded as a result of heavy rainfall. Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, there appears to be two main areas of surface water ponding within the hotspot. The first of these two areas encompasses the residential streets surrounding Mortimer Avenue and Buxton Gardens, and the second covers the commercial area to the west of Newbiggin Lane. There does not appear to be any significant overland flow entering the hotspot from outside the hotspot boundary. As detailed above, this hotpot is a residential and commercial area of Westerhope. The surface water ponding within the hotspot is therefore likely to be a product of rainfall on impermeable areas (buildings, roads etc.) and inadequate drainage. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 325 properties are at risk of flooding within the hotspot. One critical infrastructure location is also at of flooding within the hotspot; St Mark’s Primary School located on Bardon Close. Based on the Environment Agency’s Flood Map for Surface Water (deep), the two main areas of surface water ponding within the hotspot and the area north of Trevelyan Drive could potentially flood to depths greater than 0.3m during a 1 in 200 year flood event. Numerous properties and St Mark’s Primary School are therefore at risk from flood depths exceeding 0.3m during a 1 in 200 year flood event. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 161
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? One small housing site has been identified within hotspot. There may be some potential Green Roofs Limited for existing commercial development with flat roofs. Useful for attenuation flows. Further Soakaways/Infiltration investigation required into groundwater levels Yes and infiltration rates. Limited space available to install in existing residential housing areas. Potential Attenuation/Storage opportunities to installation within the Yes commercial area (west of Newbiggin Lane) and the golf course. Source Source Often used alongside roads, potential opportunities along Mortimer Avenue and Swales/Filter Drain Yes surrounding streets. Also potential opportunities west of Newbiggin Lane. One small housing site has been identified within hotspot. Retro fitting is a possibility, Permeable Paving Yes particularly within commercial area to west of Newbiggin Lane. Boundary Flow Interception N/A No One small housing site has been identified Rainwater Harvesting Yes within hotspot. Retro fitting is a possibility. Sewer capacity is known to be problem in the Increase Sewer Capacity Denton Valley Drainage Area, which the Yes hotspot site is located within. Network of combined sewers, and sewer capacity known to be an issue with a sewer Separation of foul/surface water to the south of the hotspot. Separation of foul Yes systems and surface and surface water systems, and taking surface water out of the combined sewer system is an option. Known problems with sewer capacity to the Improve maintenance regime Yes south of the hotspot site. Potential opportunities for storage along
Mortimer Avenue and surrounding streets. Flow/Storage on Roadway There are also potential opportunities for Yes Pathway installation within the commercial area (west of Newbiggin Lane). To the north of the hotspot area, flows could Manage overland flows potentially be directed to the school playing Yes fields. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Yes sewer network Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally). No development opportunities have been identified. However, planning policies and Planning policies/development development control should be taken forward Limited control at a Council wide level for action, as opposed to at individual hotspot level. Receptor Receptor One small housing site has been identified within hotspot. Retro fitting a possibility, and Improve Resilience and resistance Yes installation could be targeted at high risk properties (i.e. deep flooding). AECOM Surface Water Management Plan 162
Capabilities on project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 1 0 0 0 0 55 Maybe
Soakaways/Infiltration 1 1 2 2 1 2 1 135 Yes
Attenuation/Storage 2 1 1 2 1 1 1 135 Yes
Swales/Filter Drain 1 0 0 2 1 2 1 70 Maybe Source Source Permeable Paving 2 0 1 0 -1 0 1 55 Maybe
Boundary Flow Interception NA
Rainwater Harvesting 2 0 0 1 1 0 1 65 Maybe
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 1 0 -2 2 -1 1 1 25 Maybe water systems Improve maintenance 2 0 0 0 0 0 1 45 Maybe regime Flow/Storage on Roadway 2 1 0 1 1 1 1 105 Yes
Manage overland flows 1 1 1 1 -1 1 1 90 Yes
Pathway Improve channel capacity NA
Open up culverts NA Improve Floodplain NA Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Sites Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The housing sites present opportunities to manage surface water on site through green roofs, storage, swales, infiltration, permeable paving and rainwater harvesting. It should be noted that the feasibility of AECOM Surface Water Management Plan 163
Capabilities on project: Water implementing infiltration techniques within the hotspot depends on groundwater levels and infiltration rates, which requires further investigation. The housing site may currently be served by combined sewer systems. If this proves to be the case, development ought to remove the surface water from the combined sewers. Residential & Commercial Areas A number of source control mitigation measures have been identified as potentially appropriate within this hotspot. Source control measures that have been suggested for the hotspot include proving attenuation storage and/or retro fitting permeable paving within the commercial area to the west of Newbiggin Lane, utilising infiltration techniques to reduce surface water ponding across the hotspot and installing swales/filter drains along roads in the hotspots. Potential opportunities for installing swales/filter drains along roads include Mortimer Avenue, the surrounding residential streets and the road network within the commercial area to the west of Newbiggin Lane. It should be noted that the feasibility of implementing infiltration techniques within the hotspot depends on groundwater levels and infiltration rates, which requires further investigation. It may be possible to retro-fit green roofs on some of the commercial buildings with flat roofs off Newbiggin Lane. In addition to source control mitigation measures, a number of pathway measures are considered potentially appropriate within this hotspot. Providing storage along a number of the roads within the hotspot has been identified as an appropriate mitigation measure, as has using the roads to manage overland flows and direct flows to the school playing fields located in the north of the hotspot or the golf course to the west. Further investigation into providing storage on the existing roads and using the roads to channel flow (i.e. potentially through kerb raising and re-grading) is required. As appropriate, attenuation storage could provide formal flood storage within the school playing fields and the golf course. Based on the known capacity problems in the Denton Valley Drainage Area, which the hotspot site is located within, increasing capacity by separating the foul and surface and surface water sewers systems (i.e. taking surface water out of the combined sewer system) has also been suggested as a possible mitigation measure. Further investigation is required into the practicalities of implementing this mitigation strategy within the hotspot. Implementing an improved maintenance regime within the hotspot should also be considered, currently maintenance is carried out on road gullies where repairs are required. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH35.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH35.2 – As part of the highway improvements and maintenance work, assess the potential for storing water in the roads or channelling it overland into formal storage area that could be included in the SLR if the site came forward. AECOM Surface Water Management Plan 164
Capabilities on project: Water AECOM Surface Water Management Plan 165
Capabilities on project: Water
Hotspot Ref: NH36 Hotspot Location: Cowgate
Site Description Hotspot NH36 is a residential area of Cowgate, encompassing the eastern part of Druridge Drive and is located immediately to the north of a sports ground. At the junction of Druridge Drive and Ponteland Road (A167), a site has been identified as suitable for housing development. A second site has also been identified as suitable for housing development, along the eastern boundary of the hotspot (on Deepdale Crescent and Moorvale Lane). To the east of the hotspot, strategic green infrastructure opportunities have been identified on Nuns Moor. Northumbrian Water Capital Works Northumbrian Water is not undertaking any capital works within the hotspot or local surrounding area. Tyneside Sustainable Sewerage Study Assessment of Drainage Area The Tyneside Sustainable Sewerage Study “Strategic Level Prioritisation Methodology” identifies a number of Drainage Areas within the Tyneside area (58 in total), and based on a number of datasets provides an overall priority ranking for each individual Drainage Area. The four datasets detailed in Table 1 below are used to rank the individual Drainage Areas, and the different outputs are then combined to provide an overall priority ranking for each Drainage Area. Table 1: Tyneside Sustainable Sewerage Study Datasets Dataset Name Data Explanation NWL Capacity Map GIS pipe data and The purpose of the NWL Capacity Map analysis is connectivity. to provide a general understanding of the current hydraulic capacity of the Tyneside sewer network at DA level and identify those areas with the greatest capacity risks.
NWL Buckets Model GIS pipe data, The purpose of NWL Buckets Model analysis is to connectivity and provide a general understanding of the ability of a surface types. DA to cope with rainfall events and identify DAs with the greatest hydraulic risk.
Local Authorities Growth data in the form The purpose of Local Authorities Growth Data of Local Development analysis is to provide a general understanding of Framework Core future demands of the public sewerage system Strategies, Strategic resulting from planned growth and identify Housing Land Drainage Areas with the greatest increase in Availability demand resulting from new development. Assessments (up to 2020) and Employment Land Reviews.
Environment Agency Influence of rivers / The purpose of this analysis is to provide a watercourses and flood general understanding of the interaction between risk mapping high risk fluvial flooding locations and discharges from the public sewerage system and identify DAs with the greatest number of interactions.
The hotspot is located within the Denton Valley Drainage Area, and the results for this Drainage Area are detailed in Table 2. As Table 2 shows, the overall priority of the Denton Valley Drainage Area is 28 out of 58 Drainage Areas. It should be highlighted that the relative ranking of the Denton Valley Drainage Area is 2 out of 58 for the Northumbrian Water Capacity Map, which identifies that the Denton Valley Drainage Area has the second greatest capacity risks of the 58 Drainage Areas considered in the study. AECOM Surface Water Management Plan 166
Capabilities on project: Water
Table 2: Denton Valley Drainage Area Analysis Overall Relative rankings (58 Drainage Area Assessment considered in Tyneside study) (without weighting) Drainage Local Location Area Authority Growth Capacity Bucket' data Influence Total map model ranking of rivers ranking Priority ranking ranking (2020 ranking score horizon)
Newcastle Denton Upon Tyne 05-D26 2 45 27 42 116 28 Valley City Council * Based on data provided 19th November 2010 Newcastle City Council Records of Flooding There is one recorded incident of historic flooding within the hotspot, which is located along Whitehorn Crescent. The cause and date of this flooding incident is unknown. Based on information provided by Newcastle City Council, the hotspot does not suffer from regular flooding events. Immediately to the south east of the hotspot site, regular flooding is known to occur at a low spot along Stanfordham Road (A167). Newcastle City Council explained that flooding occurs at this location as a result of the drainage gullies not functioning appropriately, and that flooding was recorded at this location recently. Surface Water Flood Risk Based on the Environment Agency’s Flood Maps for Surface Water and Areas Susceptible to Surface Water Flooding, there appears to be one main overland flow pathway through the hotspot (to the north of Druridge Drive). There does not appear to be any significant overland flow entering the hotspot from outside the hotspot boundary. As detailed above, this hotpot is a residential area of Cowgate. The surface water ponding within the hotspot, and the overland flow pathway through the hotspot, are therefore likely to be a product of rainfall on impermeable areas (buildings, roads etc.) and inadequate drainage. Based on the Environment Agency’s Flood Map for Surface Water (1 in 200 year event; shallow) and the Environment Agency’s Areas Susceptible to Surface Water Flooding (intermediate susceptible) 291 properties and Springfield Road (A191) are at risk of flooding within the hotspot. The properties identified as being at risk of flooding are primarily located between Springfield Road and Druridge Drive and between Eastern Way and Chestnut Avenue. A few properties are also at risk of flooding to the south of Druridge Drive. Based on the Environment Agency’s Flood Map for Surface Water (deep), there are eight locations within the hotspot where flood depths could potentially exceed 0.3m during a 1 in 200 year flood event. Six of these locations are residential streets off Druridge Drive, while the other two locations are residential areas on Eastern Way and Deepdale Crescent. A number of properties are at risk from flood depths exceeding 0.3m in these locations. Springfield Road (A191) (critical infrastructure) is not considered to be at risk from flood depths exceeding 0.3m during a 1 in 200 year flood event. Managing the Risk Based on the surface water flood risk within the hotspot, potential measures to mitigate the flood risk within the hotspot have been considered. Potential mitigation measures have been considered based on a set of standard source, pathway and receptor mitigation measures which are listed in Table 3. A two step assessment process was used to assess the feasibility of implementing each standard mitigation measure within the hotspot. The first step comprised an initial screening appraisal, and the results of this initial screening appraisal are detailed in Table 3. The screening appraisal reviews the technical feasibility of implementing each mitigation measure within the hotspot. AECOM Surface Water Management Plan 167
Capabilities on project: Water
Table 3: Technical Site Specific Screening Technical Mitigation Measure Commentary Feasibility? Possibility for housing sites within hotspot. Green Roofs Not considered appropriate for existing Yes residential development. Useful for attenuation flows. Further Soakaways/Infiltration investigation required into groundwater levels Yes and infiltration rates. Possibility for housing sites within hotspot. Attenuation/Storage Limited space available to install in existing Yes residential housing areas. Often used alongside roads, and there are
Source Source potential opportunities for installation along Swales/Filter Drain Druridge Drive, Springfield Road, Whitehorn Yes Crescent and Eastern Avenue. Further investigation required. Possible during future development, housing Permeable Paving sites within hotspot. Retro fitting also a Yes possibility. Further investigation required. Boundary Flow Interception N/A No Possible for housing sites within hotspot. Rainwater Harvesting Retro fitting also a possibility. Further Yes investigation required. Sewer capacity is known to be problem in the Increase Sewer Capacity Denton Valley Drainage Area, which the Yes hotspot site is located within. Network of combined sewers, and sewer capacity known to be problem. Separation of Separation of foul/surface water foul and surface and surface water systems, Yes systems and taking surface water out of the combined sewer system is an option. Known problems with drainage gullies to the Improve maintenance regime Yes south east of the hotspot site. Potential opportunities for storage along Druridge Drive, Springfield Road, Whitehorn Flow/Storage on Roadway Yes
Pathway Crescent and Eastern Avenue. Further investigation required. Flows could potentially be directed to the Sports Ground located immediately to the Manage overland flows Yes south of the hotspot site, or Nuns Moor to the east. Improve channel capacity N/A No Open up culverts N/A No Improve floodplain storage N/A No Remove any obstructions/blockages in the Remove Obstructions Yes sewer network Possibility, but would need to be Improved weather/flood warning implemented as part of wider scheme (i.e. all Limited of Newcastle or even nationally). Possibility during future development, and housing sites within hotspot. However, Planning policies/development planning policies and development control Yes control should be taken forward at a Council wide level for action, as opposed to at individual
Receptor Receptor hotspot level. Possibility during future development, and housing sites within hotspot. Retro fitting also Improve Resilience and resistance Yes possibility and could be targeted at high risk properties (i.e. deep flooding). AECOM Surface Water Management Plan 168
Capabilities on project: Water
Following the initial screening appraisal, the short-listed mitigation measures (those considered technically feasible) were taken forward for more detailed consideration. A multi-criteria assessment of the short-listed mitigation measures is presented in Table 4. Measures scoring over 75 have been highlighted as being appropriate for further consideration. Measures scoring between 15 and 75 have been identified as possible candidates that may have something to offer and should not be discounted from any future assessment. Table 4: Multi-Criteria Assessment
Mitigation Measure Overall Technical Technical Economic Economic Short List? Short List? Carbon Cost Carbon Cost Social Impact Impact Social Sustainability Sustainability Environmental Environmental Climate Change Change Climate
Weighting 20 35 15 15 5 5 5
Green Roofs 2 0 2 2 1 2 2 125 Yes
Soakaways/Infiltration 1 1 2 2 1 2 1 135 Yes
Attenuation/Storage 2 1 1 2 1 1 1 135 Yes
Swales/Filter Drain 1 0 0 2 1 2 1 70 Maybe Source Source Permeable Paving 2 1 1 0 0 0 1 95 Yes
Boundary Flow Interception NA
Rainwater Harvesting 2 0 1 1 1 1 1 85 Yes
Increase Sewer Capacity -1 -2 0 0 -1 1 -1 -95 No Separation of foul/surface 1 0 -2 2 -1 1 1 25 Maybe water systems Improve maintenance 2 0 0 0 0 0 1 45 Maybe regime Flow/Storage on Roadway 2 1 0 1 1 1 1 105 Yes
Manage overland flows 1 1 1 1 -1 1 1 90 Yes
Pathway Improve channel capacity NA
Open up culverts NA Improve Floodplain NA Storage Remove Obstructions -1 1 1 1 0 1 1 55 Maybe Improved weather/flood 1 0 0 0 0 2 2 40 Maybe warning Planning policies/development 1 1 1 0 0 1 1 80 Yes control Receptor Receptor Improve Resilience and 1 2 -1 0 -1 1 1 80 Yes resistance
Development Sites In addition to the two housing sites within the hotspot boundary a number of others are in the vicinity. Newcastle City Council should develop planning polices to enforce source control mitigation measures to be incorporated into new developments. The housing sites all present opportunities to manage surface water on site through green roofs, storage, swales, infiltration, permeable paving and rainwater harvesting. It should be noted that the feasibility of implementing infiltration techniques within the hotspot depends on groundwater levels and infiltration rates, which requires further AECOM Surface Water Management Plan 169
Capabilities on project: Water investigation. The housing sites may currently be served by combined sewer systems. If this proves to be the case, development ought to remove the surface water from the combined sewers. Duridge Drive In addition to source control mitigation measures, a number of pathway measures are considered potentially appropriate within this hotspot. Providing storage along a number of the roads within the hotspot has been identified as appropriate mitigation measure, as has using the roads to manage overland flows and direct flows to the sports ground located to the south of hotspot or to Nuns Moor to the east. Further investigation into proving storage on the existing roads and using the roads to channel flow (i.e. potentially through kerb raising and re-grading) is required. As appropriate, attenuation storage could provide formal flood storage within the sports ground or Nuns Moor. Based on the known capacity problems in the Denton Valley Drainage Area, which the hotspot site is located within, increasing capacity by separating the foul and surface and surface water sewers systems (i.e. taking surface water out of the combined sewer system) has also been suggested as a possible mitigation measure. Further investigation is required into the practicalities of implementing this mitigation strategy within the hotspot. Implementing an improved maintenance regime within the hotspot should also be considered, as there are known problems with several road gullies to the south east of the hotspot. Receptor Mitigation Measures In terms of implementing receptor mitigation measures within the hotspot, improving resilience and resistance has been identified as potentially appropriate during future development across the hotspot. Implementing improved weather/flood warning is not considered appropriate at individual hotspot level, as it would need to be implemented as part of wider scheme (i.e. all of Newcastle or even nationally). Strategic policies and development management policies set by the Council should be local authority wide rather than area specific.
Recommendations NH36.1 – Newcastle City Council should develop planning polices through the LDF to enforce source control mitigation measures to be incorporated into new developments. NH36.2 – As part of highways improvement and maintenance works, explore potential for storing water in roads or channelling it overland into formal storage areas that could be on the sport ground to the south or school field to the north. AECOM Surface Water Management Plan 170
Capabilities on project: Water