Suffolk Coastal and Waveney District Councils Level 1 Strategic Flood Risk Assessment Appendix B Existing and Ongoing Hydraulic Modelling Studies in Waveney and East Suffolk Prepared for: East Suffolk Councils AECOM Suffolk Coastal and Waveney District Councils Level 1 Strategic Flood Risk Assessment Climate Model Flood Source Aim Scope Outcome Forecast Update Mapped Status Change East Suffolk Minor Produce floodplain mapping for the Minsmere Numerous properties at risk within Wrentham on Cover Run or Yox/Minsmere and Thorpeness Watercourse Flood Fluvial Initial Model Build 20% and 30% River, Peasenhall Gull Cove Run, River Yox, and Peasenhall on the River Yox. Several Flood Warning Flood Risk Areas Yes model update due 2019/2020 Risk Study (2006) JBA the Thorpeness Hundred watercourse. and two Flood Warning Areas proposed. Assesses the impact that sedimentation and There is sufficient capacity within the existing system to accommodate a Walpole Modelling Impact assessment vegetation growth occurring on the River Blyth at reduction in channel capacity (resulting from vegetation growth or Fluvial River Blyth model (2011) Fluvial 15% Yes and options testing Walpole has on local flood risk in order update sedimentation) without causing flood risk to residential properties during update due 2019 JBA the river maintenance regime in the village. a 1 in 100 year event. The model upgrade was part of the SFRM2 framework to provide greater detail and accurate The flood extents generated from the with-defences model show that in topographic data with revised extreme tidal levels present day scenarios the current defences provide a good protection in This model will be superseded Stour & Orwell Estuary 1.05 m sea which have been updated since the original urban areas, most of which are protected up until the 200 year event by the new Essex Norfolk and Model (2011) Tidal Model update level rise in Yes model was constructed. (0.5% AEP). However, once tide levels are raised to account for climate Suffolk Coastal Modelling 2110 A set of breach models were also constructed change, the defences are ineffective even during a 5 year event (20% Study from the with-defence model and used to carry AEP). out hazard mapping for 10 breach locations. Fluvial Alde, Ore and Hydraulic model improvements to update current Larger flood extents found at: Framlingham during the 1 in 1,000 year 15% Fromus ISIS-TUFLOW flood maps and assess the maintenance options (River Ore), Great Glemham and Stratford St Andrew (River Alde) Alde, Ore and Fromus model Yes Fluvial Model update Model (2012) for various sluices at around the Alde and Smaller flood extents found at: Framlingham during the 1 in 100 year update due 2018 JBA Fromus confluence. (River Ore), Badingham (River Alde) and Saxmundham (Fromus). Hydraulic modelling of the Chediston Halesworth Modelling Fulvial Byth model update Fluvial Initial Model Build Watercourse, Wisset Watercourse and River Yes (2011) JBA due 2019 Blyth. Revised tidal Flood Zones were marginally less extensive in the upper Essex, Norfolk & Suffolk Suffolk Estuaries Blyth To produce flood data and model outputs to tidal catchment; however, flood affects more rural areas in the lower 1.06m sea level (2012) Tidal Initial Model Build revise tidal Flood Zones 2 and 3 for the Blyth catchment. Generally, the results of this study have indicated that, with Coastal Modelling – Blyth due Yes rise in 2110 estuary. respect to still water levels, the SoP afforded by the coastal/tidal flood 2017 defences in the study area is high. Flood Risk Study of This area is now Initial model build, River Minsmere and Modelling of the complex drainage pathways of In order to minimise the flood risk in Middleton village and in the vicinity covered by the Essex, including impact Yox/Minsmere model update Leiston Drain (Sizewell) Fluvial 15% the River Minsmere and investigating their of the Sizewell Nuclear Power Stations, channel maintenance and the Norfolk and Suffolk assessment and due 2019/2020 (2013) response to potential environmental change. introduction of a third outfall structure are proposed. Open Coast Modelling options testing JBA (2017) Updated model shows that flood risk to Bungay is not as extensive as Waveney Model (2013) Updates made to the original 2005 hydraulic Waveney model update due Fluvial Model update 15% previously expected. Flood risk at Diss is greater than previously Yes JBA model. 2019/2020 expected. Debenham Village, Hydraulic modelling of the Debenham area, Increased flood outlines due to improved representation of structures. Flood Mapping including: the River Deben, The Gulls and Cherry Model update and Options modelling demonstrated that construction of an impounding No, outside of districts Extension Project Fluvial & Pluvial 15% Tree Brook and pluvial modelling of the village, options testing Reservoir on The Gulls watercourse near Aspall provides the greatest area. (2014) with associated map outputs. Followed by benefit in terms of properties protected. JBA exploration of flood alleviation options. Now superseded by the new Kirkley Stream (2014) Fluvial Initial model build Fluvial modelling of the Kirkely Stream integrated surface water and No CH2MHILL fluvial model released in 2017. Climate change Lowestoft Tidal Flood defence options in Lowestoft were The greatest flood alleviation was provided by both the proposed tidal peak level Defences (2014) Tidal Options testing evaluated, to carry forward the most beneficial barrier and Mutford Lock remaining closed throughout the duration of an No water level of CH2MHILL option for further more detailed analysis. extreme surge event. 4.35 mAOD Improvements to the original Broadlands Broads Flood Risk Hydraulic Model in the Beccles area. New Broads Model Update to Updated data, modelling, flood mapping in line with the EA’s SFRM2 Study (2014) Fluvial & Tidal Model update 20% This modelling study is ongoing; therefore, at the update this section in 2019/ In part Framework. CH2MHILL time of writing only outputs for the Beccles area 2020. were supplied by the EA for the SFRA. Prepared for: East Suffolk Councils AECOM Suffolk Coastal and Waveney District Councils Level 1 Strategic Flood Risk Assessment Climate Model Flood Source Aim Scope Outcome Forecast Update Mapped Status Change This area is now Alde and Ore Model Update existing 2011 model to simulate tidal Tidal flood risk is greater than fluvial; however, a joint tidal/fluvial event covered by the Essex, Update and Options Model update and Extreme Water events, fluvial events, joint tidal/fluvial presents a significant danger to property and life. Localised raising of Tidal & Fluvial Norfolk and Suffolk Appraisal (2015) options testing Level for 2111 combination events and potential flood defence existing Snape village defences protects a significant number of Open Coast Modelling JBA options. properties and is the most economically viable. (2017). ENS Survey & Model Build – Friston (2015) Fluvial Initial Model Build Yes JBA Lowestoft Tidal Barrier The proposed tidal gate and defence scheme are likely to increase peak This report builds on the Lowestoft Tidal – Outer Harbour Water water levels in the outer harbour, however, increase levels are not Defences (2014) study to assess the impact of Level Modelling Tidal Options testing UKCIP 09* expected to exceed water levels experienced outside the harbour wall. No the proposed flood gate and walled flood Investigation (2016) Flood risk around the harbour is actually reduced due to the presence of scheme. CH2MHILL proposed defences. Produce a new hydraulic model for the Removing 4 of the possible 5 structures in the Lothingland Model made Wrentham and Lothingland catchments. Evaluate the impact of no difference to properties at risk. Removal of the Benacre pumping Lothingland Hundred Initial model build and Fluvial 20% removing 5 key structures. Review existing 1D station resulted in increased risk during low magnitude events and Yes Modelling (2015) model review ISIS model for Wrentham. Evaluate the impact of decreased risk at high. Removal of the 3 structures in the Wrentham CH2M Hill and Halcrow removing 3 key structures. model resulted in negligible difference to properties at risk. Updated hydraulic modelling to include overtopping, breaching and hazard using the Essex, Norfolk and Extreme Tide Level and the Wave Transformation Essex, Norfolk & Suffolk Suffolk Open Coast Model. Also to produce a tool to use for real time Outputs to be provided for Stour/Orwell and Blyth. Coastal Modelling – Blyth, Tidal Updated modelling In part Modelling (2017) flood forecasting of a storm surge. Stour and Orwell expected JBA Outputs have been provided for: Kessingland, 2018 Lake Lothing, Alde, Deben, Lowestoft and Leiston. This modelling includes the Potsford Brook and River Deben Fluvial Model Review New modelling released late 2017. Yes the Melton Watercourse. Kirkley Stream (2017) New modelling released late 2017 which supersedes the previous fluvial In Level 2 of this SFRA Pluvial & Fluvial New integrated model Led by Waveney District Council. Due to be finalised in 2018. JBA Kirkley Stream modelling undertaken in 2014 by CH2M Hill. only. Fynn & Lark Fluvial Initial Model Build New model expected in 2018 No CH2M Hill * The UKCIP 09 dataset reflects the Environment Agency’s latest ‘Adapting to Climate Change Guidance, September 2011’. As advised in the guidance the UKCIP Medium emission scenarios 95 percentile relative sea level rise values have been used to generate tidal boundaries for the ‘Change Factor’ boundaries. Prepared for: East Suffolk Councils AECOM .