Persimmon Homes East

Newbattle Residential

Development

Flood Risk Assessment

August 2013

Newbattle Residential Development Level 1 Flood Risk Assessment

Contents

1 Background Information 1

1.1 Study Area and Development Proposals 1

1.2 Planning Policy and Flood Risk 2

1.3 Third Party Consultations 2

1.4 Site Hydrology 2

1.5 Ground Conditions 3

2 Flood Risk 4

2.1 Tidal Flooding 4

2.2 Fluvial Flooding 4

2.3 Surface Water (Pluvial) Flooding 5

2.4 Groundwater Flooding 5

2.5 Flooding from Public Sewers 5

2.6 Flooding from Reservoirs, Canals and Other Artificial Sources 6

2.7 Impact on Flood Risk Elsewhere 6

3 Conclusions 7

ii Newbattle Residential Development Level 1 Flood Risk Assessment

1 Background Information Fairhurst was commissioned by Persimmon Homes East Scotland to assess potential flood risks associated with the proposed residential development in Newbattle (NGR NT334 648). This Flood Risk Assessment (FRA) report has been prepared in response to comments in the Local Development Plan Main Issues Report 2013: Technical Note – Development Sites Assessment which notes that SEPA recommend a basic FRA is undertaken for the site. The report presents the findings of a qualitative assessment of flood risk. This level of assessment is considered appropriate given the early stage of the development planning process. This report considers all sources of flooding pertinent to the proposed development site and provides recommendations on further, more detailed investigations which may be required to inform the future detailed design of the development. It also recommends possible measures to mitigate residual flood risks.

1.1 Study Area and Development Proposals The proposed residential development consists of three plots and is located on the northern outskirts of Newtongrange, approximately 1.8km south of . The proposed development sites are as follows:  Plot 1 is situated immediately south of Newbattle Home Farm and is bounded by the existing B703 to the east and Ochre Burn to the south west. The 3.74ha site is currently occupied by agricultural land.

 Plot 2 is located between the existing B703 and the Beeches and is bounded by agricultural land to the north and Newtongrange housing estate to the south. The 5.23ha site is currently occupied by agricultural land.  Plot 3 having an area of 2.33ha occupies existing agricultural land and is bounded by Campbell Park to the north, the Beeches to the west and Newtongrange housing estate to the south. The development plots are located on land designated as a Conservation Area in Midlothian Council’s Local Plan, December 2008. The location of the proposed development plots is shown in Figure 1 below. No proposed development site layout and levels have been available at the time of writing.

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1.2 Planning Policy and Flood Risk Flood risk for the proposed residential development has been considered in accordance with Scottish Planning Policy (SPP): Flooding and Drainage (February 2010), Planning Advice Note 69 (PAN69): Planning and Building Standards Advice on Flooding and Policies RP8 ‘Water Environment’ and DP3 ‘ Protection of the Water Environment’ of the Midlothian’s Council Local Plan dated December 2008. SPP states that new development should not take place if it would be at significant risk of flooding from any source or would materially increase the probability of flooding elsewhere. In general, the storage capacity of floodplains should be safeguarded and any proposed landraising works should not lead to a loss of floodwater storage. Planning Policy DP3 requires residential properties for permanent occupation to be protected against at least 1 in 200yr flood event. Properties such as bungalows, ground floor flats and below ground level accommodation are considered to be of higher risk and depending on local circumstances may require an increased level of protection. The Scottish Environment Protection Agency (SEPA) has a duty to give advice to planning authorities regarding flood risk under the Flood Risk Management Act 2009, Section 72. The SEPA/Planning Authority Protocol on Development at Risk of Flooding: Advice and Consultation issued in September 2000 presents principles to be followed by the authorities regarding advice and consultation on flood risk issues. It also presents generic guidance on the requirements for undertaking flood risk assessments.

1.3 Third Party Consultations The following information has been requested/obtained as part of this flood study:  historic and current flooding issues and information on flood studies carried out in the vicinity of the proposed development area – SEPA and Midlothian Council  existing sewer records - Scottish Water (via National One Call)  LiDAR Digital Terrain Model (1m postings) – Landmark Information Group

1.4 Site Hydrology All information presented below is based on review of relevant maps and digital images as no site visit has been carried out as part of this FRA desk study. The existing ground levels have been derived from 5m contour 1:25000 OS map and confirmed using 1m LiDAR data obtained in August 2013. The most significant watercourse in the area of concern is River South Esk with a catchment area downstream of the proposed development site of approximately 148km2. The catchment of the South Esk is essentially rural with a number of reservoirs present in the upper catchment and development clusters in the lower catchment. The three development plots are located within a catchment of the Ochre Burn, a minor tributary of the River South Esk. The Ochre Burn emerges from a culvert under an industrial estate, immediately south of the Plot 1, west of Newbattle Road, and flows in an open channel following field boundaries down to the Newbattle Home Farm. Two short culverts under access tracks are evident along its route. It is then culverted for an approximate distance of 180m before flowing in an open channel and a short culvert along the B703. The burn then flows in an uninterrupted culvert to its confluence with the River South Esk near Newbattle Bridge. It is uncertain however what route this culvert follows.

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A short section of an unnamed tributary of the Ochre Burn immediately north west of the Campbell Park is evident. The full extent of the tributary is unknown due to its being potentially culverted under the Campbell Park. A short section of an open channel is also evident in the eastern part of the Plot 3. The origin and extent of the water feature is unknown but it may be either an extension of the unnamed tributary of the Ochre Burn or be related to the disused mineworkings present in that area. Further culverting of the tributary may also be present under the Newtongrange development cluster to the south. The full extent of the Ochre Burn and its catchment is uncertain due to its being culverted under the Newtongrange housing estate. The upper and lower parts of the natural catchment are predominantly rural however the middle part has undergone extensive modifications due to urbanisation. Scottish Water sewer records have been reviewed as part of this FRA to aid understanding of the Ochre Burn catchment. The Ochre Burn catchment area at its confluence with the River South Esk, as derived from the FEH CD-ROM v.3, is 3.64km2. However the actual catchment area is decreased by the Newtongrange development cluster which drains via combined sewers away from the Ochre Burn catchment. A small pond is also present immediately to the west of the Ochre Burn, at the north west corner of Plot 1. The source of inflow to the pond is unknown. Another minor tributary of the River South Esk, Mary Burn, is located approximately 400m from the eastern extent of the Plot 3. The upper catchment of the Mary Burn is urbanised whereas the lower catchment is rural with largely uninterrupted open channel (except for potential short culverts under woodland paths) present within an area of woodland to its confluence with the River South Esk. Its catchment at that point, as derived from the FEH CD-ROM v.3, is 0.66km2. The actual catchment area may differ due to the extent of built-up area potentially draining via public sewers away from the Mary Burn’s catchment. No public sewer records have been sourced for this area due to the relative distance from the development site. The LiDAR DTM indicates that Plot 1 is located on ground with levels between 81.8mAOD and 67.8mAOD with ground generally falling in a north westerly direction towards the Ochre Burn. Along the western boundary of the site, the LiDAR suggests that a short strip of ground may fall away from the right bank of the watercourse, before flattening out perpendicular to the direction of the channel. Plot 2 lies on a ground falling in a north westerly direction, at levels between 87.2mAOD and 72mAOD. Plot 3 is situated on ground with levels between 90mAOD and 85.0mAOD with ground also falling in a north westerly direction.

1.5 Ground Conditions No site investigation has been undertaken to date thus no detailed information on ground conditions and associated groundwater table in the vicinity of the site is available. A review of the 1:25000 OS map has identified two wells some 600m and 780m north of the Plot 3. It is unknown however how the wells are fed. Based on Sniffer groundwater vulnerability maps of Scotland the eastern part of the country is underlain by low permeability deposits.

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2 Flood Risk Examination of published SEPA River & Coastal flood maps has concluded that the development plots are not shown to be at risk of coastal and fluvial flooding from the River South Esk. The SEPA flood maps are based on a predicted 200yr flood event (i.e. the flood with a 0.5% chance of occurring in any single year). The maps were developed to provide a strategic overview of flood risk and are ‘indicative’ only. As such they do not represent a definitive opinion on flood risk for individual properties or development sites. They also do not account for flooding arising from sources such as surface water runoff, surcharged culverts or drainage systems. The flood maps do not include flood extents for the watercourses of catchment areas less than 3km2 thus no floodplain envelopes are available for the Ochre Burn and the Mary Burn. The ‘Strategic Flood Risk Assessment (SFRA), Main Issues Report 2013’ prepared by Midlothian Council has also been reviewed as part of this flood study. The SFRA has revealed some flooding incidents in the vicinity of the proposed development site, especially in the area of the Beeches and the Ochre Burn. SEPA and Midlothian Council have been consulted in relation to historic and current flooding issues in the vicinity of the proposed development site. SEPA have records of two flooding incidents from the Ochre Burn at the B703 culvert in November 2002 and October 2005. Flooding is reported to have affected the road at that location. It is not clear from the information available if the flooding related to the main Ochre Burn or its tributary. SEPA have also drawn attention to possible effects of the historic mining on groundwater paths leading to emergence of springs, particularly in the area of Campbell Park.

Midlothian Council’s response was awaited at the time of writing.

2.1 Tidal Flooding Based on the location and topography and in line with the SFRA the proposed development site is not considered at risk of inundation from coastal waters.

2.2 Fluvial Flooding The proposed development is positioned outwith the 1 in 200yr flood extent of the River South Esk and, given the difference in elevation, there is no risk of fluvial flooding from the watercourse during the design flood event to any of the proposed development plots. The western edge of Plot 1 may be at risk of flooding from the Ochre Burn. This could arise through exceedance of channel capacity or failure/blockage of conveyance infrastructure. Local ground levels suggest that water spilling out-of-bank in the upstream reach of the watercourse could flow into the site for a short distance before passing through the site, parallel to the channel. Levels suggest that any flood water would return to the burn at the north west corner of the Plot and would then be channelled away from the site. The potential issue identified during this assessment is consistent with the information provided in the Midlothian Council’s SFRA. Further analysis, including hydraulic modelling would be required to predict the extreme flood extents for the Ochre Burn and establish appropriate mitigation measures. For masterplanning purposes, a buffer strip should be considered along this edge of the site and development should be located outwith this area. Due to the Plots 2 and 3 being positioned on higher grounds the flood risk posed to them by the Ochre Burn is considered much lower. The open watercourse section of the tributary shown on some

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OS mapping to lie along the eastern edge of Plot 3 may also require to be assessed in detail. Any culvert associated with the tributary in the vicinity of the site should also be investigated. Based on the catchment size, topography and significant distance of the Mary Burn to the proposed development the probability of flooding of the development plots from that watercourse is considered as low.

2.3 Surface Water (Pluvial) Flooding Pluvial flooding occurs during extended rainfall events leading to saturation of the ground and inability of the underlying soil to drain rainwater away. Due to limited absorption capacity of the saturated ground (or underlying impermeable soils) the excess water causes surface flooding. Flat, low lying areas are the most vulnerable in terms of pluvial flooding. Considering that the proposed development plots are located on sloping ground there is no risk of surface water ingress onto the sites from the north. However there is a potential for surface water runoff entering the sites from the built-up areas to the south of the plots. It would be the case during a failure of the surface water drainage infrastructure within the Newtongrange urban area. To protect the proposed development against pluvial flooding appropriate drainage arrangements should be incorporated along the southern perimeters of the three development plots. Residual risk can further be mitigated by setting development finished floor levels above existing ground levels.

2.4 Groundwater Flooding Groundwater flooding occurs commonly in low-lying areas underlain by permeable rock. Based on the SFRA, groundwater flooding is not considered a significant hazard in Scotland. Based on the presence of low permeability soils and local topography the risk of development flooding from groundwater is considered as low. It is noted however based on the evidence of historic mining, especially within an area of the proposed Plot 3 that there is a potential for a watercourse to sink and re-emerge down gradient due to altered natural groundwater flow paths.

2.5 Flooding from Public Sewers A review of the Scottish Water record plans has identified an extensive combined and surface water sewer network within the Newtongrange housing estate, south of the proposed Plots 2 and 3. The combined effluent from the urban area is conveyed in a 375mm pipe through an industrial estate to the west of the Newbattle Road. The sewer then crosses proposed Plot 1, denoted as a PFI sewer, and runs in a northerly direction passing the western boundary of the Newbattle Home Farm. The gravity sewer discharges to Seafield treatment works in Edinburgh. PFI Storm Works are present in the industrial area to the south of the Plot 1. The system includes an overflow to the Ochre Burn on the southern boundary of the Plot 1. The frequency of the overflow and its likely rates are currently unknown. A network of water mains is also present within the development cluster to the south of Plots 2 and 3. A risk of the site flooding from the existing sewers cannot be quantified due to lack of information on the sewers and unconfirmed finished development site levels. However based on existing topography of the area any flooding caused by sewer capacity exceedance or failure would potentially overflow in a northerly direction towards the proposed development plots. The probability of flooding to Plot 1 is increased due to the PFI Storm Works overflow into the Ochre Burn. Further details of the operation

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of the overflow should be sought as part of a detailed flood risk assessment for the site to quantify flows if possible and inform the development of appropriate mitigation. To protect the proposed development against flooding from public sewers appropriate drainage arrangements should be incorporated along the southern perimeters of the three development plots. Residual risk can further be mitigated by setting development finished floor levels above existing ground levels.

2.6 Flooding from Reservoirs, Canals and Other Artificial Sources There are no reservoirs, canals or other artificial water features in the vicinity of the development site thus there is no risk of inundation from such sources.

2.7 Impact on Flood Risk Elsewhere The proposed development will be constructed on an existing greenfield site, currently under agricultural use. No drainage proposals for the development are available at this stage however it is anticipated that any adverse impact on the existing water environment will be mitigated by adoption of sustainable drainage measures (SuDS). Direct or indirect surface water discharges from roofs and hardstanding areas to the natural water environment should be restricted to ‘greenfield’ runoff rates to mitigate against increased flood risk elsewhere. The SuDS design should be developed in accordance with the Local Planning Policy DP3 and relevant guidance documents. Consideration should also be given to an overland flood route in case of internal drainage failure/blockage to safely convey the excess waters away from the buildings. It is envisaged that the proposed development’s foul drainage will discharge to the nearby public sewers. The discharge will impose extra demand on public drainage infrastructure thus consultation with Scottish Water should be undertaken to confirm viability of connection of the proposed site drainage into public sewer.

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3 Conclusions The initial flood risk assessment has demonstrated that the majority of the proposed development site would be considered at low risk of flooding. Any residual flood risk can be effectively managed through appropriate development layout and mitigation where required. Further, detailed analysis will be required to quantify flood risk associated with the Ochre Burn. For initial masterplanning purposes, a buffer strip should be respected beyond the banks of any open watercourse sections. Any development ground modelling should avoid the creation of low lying areas and allow for overland flow to be routed around and away from buildings.

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