Flood Risk Assessment Project Proposed Replacement Dwelling Garside Street / Shelley Street | Worksop | Nottinghamshire | S81 7BH Location Chris Yorke Adi Krasniqi Lyndale | Harworth Road Managing Director Director Blyth | Worksop BSc(Hons) | MCIAT BSc(Hons) Nottinghamshire | S81 8HQ C.Build E | MCABE Tel: 01909 591871 E. [email protected] E. [email protected] www.yorkearchitecture.com M. 07828 789 651 M. 07929 456 125 Contents 0.0 Introduction 1.0 Development and Site Location 2.0 Sequential and Exceptions Test Statement 3.0 Definition of Flood Hazard 4.0 The Probability of Flooding 5.0 Climate Change Effect 6.0 Flood Risk Measures 7.0 Off Site Impacts 8.0 Residual Risks Appendices Appendix A – Site Location Appendix B – Site Plan Appendix C – Site Levels Appendix D – Environment Agency and SFRA Information Appendix E – Wastewater and Drains Map Appendix F – Evacuation Plan Appendix G – Glossary of Terms 1.0 Introduction The assessment has been undertaken in accordance with the National Planning Policy Framework (NPPF). It uses information of the existing topography, existing surface water drainage systems, historical flood records and simulated flood maps. This Flood Risk Assessment has been prepared in support for a proposed development of a 1No replacement dwelling located / accessed from Garside Street, Worksop, S80 2DD. Relevant information was sought from the Environment Agency (EA) and the local flood authority (Nottinghamshire County Council). Possible sources of flooding will be evaluated to determine the risk they pose to the development site. The effect of climate change will also be considered, and any off-site impacts caused, by the development. Should the risk of flooding prove to be significant, the report will endeavour to minimise the impact on the development and the local area throughout its design life to protect against the threat to life. In summary, this report confirms the proposal can be developed safely, with negligible impact on flood risk off-site. In summary the finished floor level (FFL) of the proposed dwelling is to be a minimum of 30.96mAOD to protect the dwelling against flooding. Two bedrooms will be located on the first floor to provide a safe refuge for the occupants should evacuation not prove achievable, although evacuation from the development site is a quick and easy affair given the proximity to the flood zone 2/3. Any dwelling within 8m of the top bank of the River Ryton will require permission from the Environment Agency. 2.0. Development and Site Location 2.1 Site Location The site is in the township of Worksop, 0.70km southeast of the city centre. Worksop is the principal town in the Bassetlaw district, lying on the River Ryton at the northern edge of the Sherwood Forest. The site is bordered by residential dwellings with Priorswell Recreational Ground along its east and southern borders. There is a large Morrison’s supermarket 120m north, which is part of a large commercial/services park. Grid reference E459450, N379107. Refer to Appendix A for the site location. The nearest main watercourse, the River Ryton that runs adjacent to the sites southern border. The Chesterfield Canal runs a similar course to the River Ryton on its northern bank through Worksop. The canal passes over the River Ryton around 640m to the east where it continues to follow the river on its south bank for a distance before diverging at Ranby, 6.15km northeast. The site sits in between the River Ryton and the Chesterfield Canal as they flow east out of Worksop. 2.2 Site Description The proposed development is to demolish Rose Cottage and erect a new dwelling in approximately the same location. The new dwelling will benefit from the same large garden as the original. A rough site plan is attached in Appendix B. The gross site area is approximately 0.15Ha. The site ranges from 30.12 to 30.80 metres Above Ordnance Datum (mAOD). The topography is relatively level across the site, with a gentle gradient slope southeast towards the River Ryton. The site levels are provided by UK Map Centre, available in Appendix C. From BGS data the bedrock geology is noted as Lenton sandstone formation – sandstone with the potential for Alluvium superficial deposits - clay, silt, sand and gravel. Nearby BGS borehole data also indicates this and indicates the potential presence of groundwater at 3.00m below ground. 2.3 Classification of Vulnerability Table 2 of the Technical guidance to the NPPF, the classification of the proposed development is in the ‘More Vulnerable’ category. 2.4 Flood Zone Classification The Environment Agency’s flood map shows that the development site is located within a Flood Zone 2. This zone comprises land assessed as having between a 1 in 100 and 1 in 1,000 annual probability of river flooding (1% – 0.1%), or between a 1 in 200 and 1 in 1,000 annual probability of sea flooding (0.5% – 0.1%) in any year. (Appendix D). 2.5 Local Development Plan The Bassetlaw Local Development Plan (BLDP) is intended to address the district’s housing and economic needs, taking into consideration other social and environmental policies, by 2037. The BLDP calls for 9087 homes by 2037, by making best use of available land. The local plan covers the whole of Bassetlaw (Figure 1). Paragraphs 3.23, 3.24 of the BLDP identify and need for additional housing in the district to meet the issues for an expanding population. Also identified is the regeneration and renewal that an increase in housing has spearheaded, acting as a catalyst for investment. By increasing housing in the district, it is the hope to attract new industry and national chains. Figure 1 - Bassetlaw District Worksop, where the development site is located is planned to grow in a sustainable manner, with new roads and infrastructure. It is an area where infill housing developments are actively encouraged, as the towns principal district. Paragraph 5.1.16 of the BLDP identifies Worksop as the most sustainable location for significant growth and the best location to deliver the goals of the spatial strategy. Worksop is a priority development site, due to its ability to expand. Worksop will deliver some 2180 new dwellings over the plan period. The other major towns for renewal are Retford and Harworth, although the approach to renewal is different to that of Worksop. Policy ST1 actively encourages the use of greenfield sites to bring change about as part of the spatial strategy. Although the development site is greenfield it is infill and does not increase the urban footprint. The settlement can be seen in Figure 2 below. Figure 2 - BLDP Settlement Hierarchy 3.0 Sequential and Exceptions Test In accordance with the Department for Environment, Food and Rural Affairs and the Environment Agency’s published guidance on the sequential and exceptions tests (developments that don’t need a sequential test) ‘You don’t need to do a sequential test if one has already been carried out for a development of the type you’re planning (eg a residential development) for your site’ A sequential test has already been carried out for this site on a previous application, however, more importantly, this is an application for a replacement dwelling and as such there is no increase in dwelling numbers and no increase in flood risk or the number of households at risk from flooding. 4.0 Definition of the Flood Hazard The sources of flooding that could potentially affect the site are the following: - • Flooding from water courses o River Ryton o Chesterfield Canal o Chesterfield Canal Feeder o Sandhill Lake • Flooding from land • Flooding from sewers • Flooding from ground water • Flooding from reservoirs A Main River Map is attached in Appendix D. 4.1 The River Ryton In the case of the River Ryton it is considered that fluvial flooding represents the worst- case scenario rather than tidal flooding, and therefore fluvial flooding is considered over tidal flooding. The development sites south border abuts the north bank of the River Ryton. The EA information includes modelled water level results for various defended storm events of the River Ryton. Table 1 below details a summary of the information most relevant to the site. Refer to Appendix D for EA data. The EA have not provided any floodplain heights or crest levels for this model. Table 1; - Defended modelled results of the River Ryton at the points closest to the site. From table 1 the levels for a 0.1% (1 in 1000 year event) from the relevant node points is 30.36mAOD. With a minimum finished floor level (FFL) of 30.96mAOD, 600mm above the 1 in 1000 year event, adequate protection against flooding is provided for the lifetime of the development. The 30.96mAOD FFL is 730mm above the predicted flood level for a 1 in 100 year event, with climate change taken into consideration. The Bassetlaw District Council 100 year with climate change flood depth (Appendix D) predicts the southern half of the site would be the worst affected, inundated with water to a maximum depth of 0.5m in such an event. Interpolating the flood depth against the ground levels from the UK Map Centre data (Appendix C), the flood depth is 30.80mAOD. The minimum FFL of 30.96mAOD is 160mm above the 1 in 100 year +CC event SFRA scenario. A source of flooding is identified as overtopping Priorswell Road that flows into Shelley Street during a 1 in 100 year storm event (Appendix D). This is confirmed in the Bassetlaw council Dynamic Map which shows the flow moving along Shelley Street from Priorswell Road (Appendix D). For a 1 in 100 year flood event the indicated flood heights are only 0.08m.