Our Ref: J-14088-01-HG 17th December 2020 Mr Hudson 10 Fulmar Road Mead Vale Weston-Super-Mare BS22 6YU Re: Flood Risk Assessment – 10 Fulmar Road, Weston-Super-Mare Introduction Mr Hudson is proposing a new build dormer house at 10 Fulmar Road, Mead Vale, Weston-Super-Mare. As part of the planning process it has become apparent that the site is at risk of flooding. According to the Environment Agency (EA) indicative flood map (Figure 2) the site appears to be located in Defended Flood Zone 3 and is therefore at a risk from flooding. As such, Mr Hudson has commissioned Nijhuis Industries Ltd to undertake a Flood Risk Assessment (FRA) for the site. This report comprises the FRA for the proposed development, in line with The National Planning Policy Framework (NPPF) and Planning Practice Guidance (PPG). Site Description The approximate OSGR for the site is ST 35770 62196. The site location is shown in Figure 1 below. At present the site is occupied by the existing garage for 10 Fulmar Road. In a wider context the site is located in the centre of Weston-Super-Mare. Figure 1. Site Location Plan SOLID SOLUTIONS IN A FLUID WORLD Nijhuis Industries UK & Ireland | Nanjerrick Court - Allet - Truro - TR4 9DJ - United Kingdom | T +44 (0)333 7000 007 | www.nijhuisindustries.com/uk [email protected] Registered Office: Chy Nyverow - Newham Road - Truro - Cornwall - TR1 2DP | Registered in England No. 4785670 Figure 2. EA Flood Map Extract Assessment of Flood Risks The EA indicative flood map takes into account fluvial (river) and tidal flooding only, therefore an assessment of other potential flood risks is undertaken below. Overland/Surface Water The site is located in the heavily urbanised area of Weston-Super-Mare. As such it is considered that overland flows will be intercepted and diverted, generally into existing drainage features. In addition to this the Environment Agency risk of surface water flooding map (Figure 3 below) shows that the site itself is at very low risk of surface water flooding. There is a low risk of flooding to Fulmar Road located adjacent to the property, this flooding is anticipated to be no greater than 300mm and is limited to the highway. As such this mechanism of flooding will not be discussed further. SOLID SOLUTIONS IN A FLUID WORLD Nijhuis Industries UK & Ireland | Nanjerrick Court - Allet - Truro - TR4 9DJ - United Kingdom | T +44 (0)333 7000 007 | www.nijhuisindustries.com/uk [email protected] Registered Office: Chy Nyverow - Newham Road - Truro - Cornwall - TR1 2DP | Registered in England No. 4785670 Figure 3. EA Risk of Surface Water Flooding Map Groundwater Flood Risk The North Somerset District Council, Strategic Flood Risk Assessment (SFRA) highlights that the area is predominantly underlain by low permeability clayey soils and, therefore, is unlikely to be at significant risk from groundwater flooding. In addition to this, there is little evidence from historic flood data that there is a risk from groundwater flooding. Groundwater will not be considered further in this report. Flooding as a result of Development The proposal is the development of a dormer dwelling to replace the existing garage at 10 Fulmar Road. The footprint of the dwelling is anticipated to slightly larger than the existing garage. As such it is considered that there will be a slight increase to the impermeable area on the site. It is anticipated that the new dwelling with have a surface water drainage scheme implemented for the proposal. This mechanism of flooding will not be considered further in this report. Fluvial (River Flooding) As part of the FRA a flood information request was submitted to the Environment Agency (EA). The information obtained provided details on fluvial and tidal flooding. This information included within Annex B. The information for fluvial flooding for the site gave levels for a series of nodes on the nearby watercourse. The closest node to the site has been considered. Based on this node the flood levels for the site are as follows: 1 in 100 year level: 5.28m AOD 1 in 100 year with 20% climate change: 5.29m AOD 1 in 1,000 year: 5.30m AOD SOLID SOLUTIONS IN A FLUID WORLD Nijhuis Industries UK & Ireland | Nanjerrick Court - Allet - Truro - TR4 9DJ - United Kingdom | T +44 (0)333 7000 007 | www.nijhuisindustries.com/uk [email protected] Registered Office: Chy Nyverow - Newham Road - Truro - Cornwall - TR1 2DP | Registered in England No. 4785670 It is noted that the EA did not provide an allowance for climate change in line with the current guidance of 40%. However, when examining the information given it is thought that when a 40% allowance for climate change is considered the flood level would not be greater than the 1 in 1,000 year level. The proposed Finished Floor Level (FFL) of the dwelling is 5.80m AOD. The ground level surrounding the proposed dwelling is 5.52m AOD. As such it is deemed that the site is not deemed to be at risk from fluvial flooding. Tidal Flood Risk With regards to the tidal flood risk to the site the information from the EA included the highest recorded historic tidal level for Weston-Super-Mare (from 1981) which is to be considered as the tidal flood level they have given for the site. This flood level is 8.10m AOD. The EA tidal flood levels do not include an allowance for climate change. An allowance for sea level rise due to climate change over the lifetime of the development should be considered. Information on climate change allowances has been outlined by the Environment Agency within the ‘Flood risk assessments: climate change allowances’ guidance shown online. According to Table 3 of this document it is estimated that the sea level rise for a residential property in South-West England is 1.21m over 100 years. Therefore, the tidal flood level with an allowance for climate change is 9.31m AOD. Weston-Super-Mare is defended from tidal flooding. The Sea Wall in the North of the Bay was upgraded in 2010 to provide a defence standard of a 1 in 200 year return period. The minimum design level of the Weston-Super-Mare sea wall is 9.05m AOD, but has been designed to be raised to a level of 9.55m AOD. It is anticipated that defences will be maintained for the lifetime of the development due to the high population density of Weston-Super-Mare which is being protected by the current defences. Flood Risk Summary Based on the information outlined above, the site is deemed to be free from fluvial flooding. The site is currently defended from tidal flooding but is at residual risk from tidal flooding should the defences fail. Mitigation Measures The site is free from fluvial flooding and is currently protected from tidal flooding and is expected to be defended for the duration of its lifetime. Nevertheless, the following mitigation measures are recommended as best practice. - Any construction methods and techniques to be flood resilient/resistant where possible. Further advice is areas at risk of flooding is available from Improving Flood Resilience of New Buildings available at: http://www.planningportal.gov.uk/uploads/br/flood_performance.pdf - It is recommended that the site should sign up for the Environment Agency’s flood warning system for the area. This will ensure prior warning of a possible flood event and allow adequate time to prepare for flooding. EA standing advice is given below: SOLID SOLUTIONS IN A FLUID WORLD Nijhuis Industries UK & Ireland | Nanjerrick Court - Allet - Truro - TR4 9DJ - United Kingdom | T +44 (0)333 7000 007 | www.nijhuisindustries.com/uk [email protected] Registered Office: Chy Nyverow - Newham Road - Truro - Cornwall - TR1 2DP | Registered in England No. 4785670 Figure 4. EA standing advice Access and Egress The nature of tidal flooding means that it is predictable in advance and as such, would allow time for residents to evacuate prior to a tidal flood event. The main access and egress for the site is via the existing route along Fulmar Road. The access road is also expected to be protected from tidal flooding for the lifetime of the development. Figure 3 shows that parts of the access roads are at a low risk from surface water flooding. However, the risk is minimal and access should still be possible. It is recommended that occupants of the site sign up to the Environment Agency flood warning service. However, in the unlikely event of inhabitants being unaware of an impending flood of sufficient magnitude to inundate the site, a refuge space is provide by the inclusion of a first floor levels included in the design of the dormer. This can act as a refuge space during the peak of the flood. Due to the nature of tidal flooding, the maximum time that the site may be at risk from flooding is approximately 3.5 hours for an extreme tidal flood event with an allowance for climate change undefended event at peak tide, this is illustrated in Figure 5 using the rule of twelfths. Considering the scale of the development, a refuge of this nature is deemed appropriate. SOLID SOLUTIONS IN A FLUID WORLD Nijhuis Industries UK & Ireland | Nanjerrick Court - Allet - Truro - TR4 9DJ - United Kingdom | T +44 (0)333 7000 007 | www.nijhuisindustries.com/uk [email protected] Registered Office: Chy Nyverow - Newham Road - Truro - Cornwall - TR1 2DP | Registered in England No. 4785670 Figure 5. Rule of Twelfths Illustrating Maximum Time the Site is at Risk of Tidal Flooding Policy The proposed dormer dwelling has been shown to be located within Flood Zone 3 albeit defended.