SEVERN ROAD RESOURCE RECOVERY CENTRE FLOOD RISK ASSESSMENT REF 402.0036.00374 September 2009
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management i PPS25 Flood Risk Assessment October 2009 CONTENTS 1.0 INTRODUCTION... 1 1.1 Context... 1 1.2 Site Location and Features... 1 1.3 Hydrological Features... 2 1.4 Geology and Hydrogeology... 2 1.5 Development Proposals... 3 1.6 Flood Zone Classification... 4 1.7 Flood Risk Vulnerability... 4 1.8 Flood Risk Compatibility (PPS25 Table D.3)... 4 1.9 Sequential Test and Sequential Approach... 4 1.10 Exception Test... 5 2.0 SOURCES OF INFORMATION... 7 2.1 Flood Zone Map and Flood Defence Data... 7 2.2 Historic Flooding... 7 2.3 Strategic Flood Risk Assessment... 7 2.4 Topographical Data... 7 2.5 Geological Data... 7 3.0 FLOOD RISK ASSESSMENT... 8 3.1 Flood Risk Assessment Methodology & Objectives... 8 3.2 Project Scope... 9 3.3 Screening Study... 9 3.4 Scoping Study... 9 3.5 Flood Levels... 9 3.6 Existing Flood Defences... 10 3.7 Technical Assessment of Flood Risk... 10 3.8 Residual Risk Assessment... 14 4.0 PROPOSED MITIGATION MEASURES... 17 4.1 Siting of Built development... 17 4.2 Finished Floor Levels... 17 4.3 Flood Warning System and Evacuation Plan... 18 4.4 Safe Refuge... 18 4.5 Safe Route of Access / Egress... 19 4.6 Flood Resilience... 19 4.7 Hydrostatic Pressure Resistance... 19 4.8 Maintaining Site Operations... 19 4.9 Flood Storage Compensation... 20 4.10 Site Drainage - Application of Sustainable Drainage Systems... 20 5.0 SUMMARY AND CONCLUSIONS... 23 6.0 CLOSURE... 25 TABLES Table 1: Existing Impermeable Area Coverage... 2 Table 2 : Proposed Impermeable Area Coverage... 3 Table 3: Potential Risk Posed by Flooding Sources... 9 Table 4: SuDS Sustainability Hierarchy... 22
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management ii PPS25 Flood Risk Assessment October 2009 APPENDIX APPENDIX A: APPENDIX B: APPENDIX C: APPENDIX D: APPENDIX E: APPENDIX F: APPENDIX G: APPENDIX H: Site Location Plan and Site Photographs Lower Severn IDB Watercourse Plan & Correspondence Development Proposals Environment Agency Flood Zone Map & EA Correspondence Topographical Survey Extracts from Avonmouth / Severnside SFRA Wessex Water Sewer and Water Main Records Flood Defence Breach Analysis
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 1 PPS25 Flood Risk Assessment October 2009 1.0 INTRODUCTION 1.1 Context Consulting Limited () has been appointed by Viridor Waste Management to undertake a Flood Risk Assessment (FRA) to inform an Environmental Statement to support a planning application for the redevelopment of the former Sevalco chemical works site as a Resource Recovery Centre at Crooks Marsh, Avonmouth, near Bristol. This FRA report has been completed in accordance with guidance presented in Planning policy Statement 25 (PPS25) 1 and supplementary Practice Guide 2, and has been prepared under the direction of a Technical Director of who specialises in flood risk and drainage infrastructure matters. The site falls within Lower Severn Internal Drainage Board (LSIDB) jurisdiction in terms of the planning consultation process on flood risk and surface water management. This FRA draws upon recent dialogue and correspondence with Development Control and Planning Liaison staff at the Environment Agency (EA) and engineering staff at LSIDB. 1.2 Site Location and Features The site is located approximately 3.5km north east of the centre of Avonmouth, near Bristol. The south west boundary of the site is with Severn Road and the eastern boundary abuts Albeton Lane. Seabank Power Station is sited 200m north-west of the site and the eastern boundary adjoins existing industrial development. The Chittening Industrial Estate is located approximately 300m south west of the site. Refer to Site Location Plan in Appendix A. The application site area covers 8.3ha. Existing and former land uses are heavy industrial. Figure 1: Aerial Photo of Site 1 Planning Policy Statement 25 : Development and Flood Risk (Communities and Local Government, 2006) 2 Planning Policy Statement 25 : Development and Flood Risk : Practice Guide (Communities and Local Government, 2008)
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 2 PPS25 Flood Risk Assessment October 2009 The existing building footprint and other impermeable areas are depicted in Figure 1 and summarised in Table 1 below: 1.3 Hydrological Features Table 1: Existing Impermeable Area Coverage Component Area (m 2 ) Main Works Building 3,109 2 no. Circular Tanks 3,610 Lagoons 1,840 Settlement Tanks 454 Additional Hardstanding Areas 35,310 Total 44,323 The site is located adjacent to the mouth of the tidal River Severn, approximately 850m to the east of the Severn Estuary flood defences. An unnamed drain runs around the eastern boundary of the site adjacent to Albeton Lane and the southern boundary adjacent to Severn Road, continuing west before draining southwesterly, eventually outfalling to Stuppill Rhine, 290m south west of the site. The Stuppill Rhine outfall to the Severn Estuary is tidally influenced, with backflows restricted by a flap valve arrangement. Refer to LSIDB watercourse plan in Appendix B. Further unnamed drains outfall via the northern site boundary to nearby Monks Well Rhine, then northwards to its confluence with Red Rhine. The Red Rhine outfall to the Severn Estuary is located to the north of Seabank Power Station at New Pill Gout. The outfall is tidally influenced, with backflows restricted by a flap valve arrangement. The existing site is drained by a private surface water sewer network, and runoff tends to shed off to the local Rhine networks to the north, south and east of the site via the pipework during nominal storm events, and by overland flood flow routes under more extreme conditions.. The site comprises a large lagoon, 4 concrete lined settlement tanks, an overflow tank and a single tank for storage of water prior to offsite discharge are located in the eastern portion of the site. Two surface water tanks are also located in the northwestern area of the site adjacent to the former Medium Thermal Plant. 1.4 Geology and Hydrogeology The published geological map 3 for the area indicates that the proposed development is underlain by Estuarine Alluvium (Tidal Flat Deposits), comprising of organic rich clay and silt, which is underlain by Triassic Mercia Mudstone Group. An in-crop of coal lies unconformable at the base of the Mercia Mudstone at some depth beneath the site. The in crop lies in a synclinal structure and is recorded on the geological map at a horizontal distance of approximately 300m to the north-west (nearest distance). 3 British Geological Survey Sheet 264-Bristol (1:50,000 Scale) Solid an Drift geology, 2004
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 3 PPS25 Flood Risk Assessment October 2009 A ground investigation was undertaken in June 2009. The strata encountered during the intrusive site works in June 2009 are summarised below. Made Ground was encountered across the entire site to depths of between 0.15 and 1.7mbgl and comprised of gravelly clay, clayey gravel, cobbles and boulders and sandy clay. Alluvium was encountered across the site beneath the Made Ground in all areas. The Alluvium generally comprised of grey mottled black silty clay and silt becoming sandy with depth; At the base of the Alluvium a layer of sandy grave or gravelly silt and clay was encountered and either thought to be a series of braided channels or coming into weathered Mercia Mudstone; The Mercia Mudstone was proven from a depth of between 10.50m and 16.00mbgl and consisted of red dolomitic siltstone and mudstone. The published Groundwater Vulnerability Map 4 for the area classifies the estuarine alluvium as a Non-Aquifer which shows negligible permeability and an insignificant water resource. The NRA regional appendix 5 classifies the Mercia Mudstone as a Minor Aquifer, with unpredictable groundwater within local sandstone bands and predominate flow mechanism through fractures. 1.5 Development Proposals Viridor Waste Management wish to redevelop the site in order to provide a Resource Recovery Centre. Refer to development proposals in Appendix C. The proposed building footprint and other impermeable areas are listed within Table 2 below: Table 2 : Proposed Impermeable Area Coverage Component Area (m 2 ) Resource Recovery Centre 26,650 Car Parking 2,516 Bottom Ash Storage 6,000 Pretreatment Area 3,600 Vehicle Workshop 1,550 Additional Hardstanding Areas 36,650 Total 76,966 4 National Rivers Authority, now the environment Agency, Policy and Practice for the Protection of Groundwater, Groundwater Vulnerability Sheet 37 Southern Cotswold (1:100,000 Scale) 5 National Rivers Authority, now the Environment Agency, Policy and Practice for the Protection of Groundwater, Regional Appendix, Wessex Region
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 4 PPS25 Flood Risk Assessment October 2009 1.6 Flood Zone Classification Based upon the Flood Zone Maps (refer to Appendix D) published by the EA, the entire site is shown to lie within high probability Flood Zone 3 which represents an annual probability of greater than 0.5% of a tidal flood occurring in any one year or greater than 1% of a fluvial flood occurring in any one year. The LSIDB and EA do not consider 6 any area behind the flood defences on the River Severn to be designated as functional floodplain. The site is therefore located within Flood Zone 3a. 1.7 Flood Risk Vulnerability The proposals include the provision of Waste Treatment Facilities (non-hazardous), General Industry, Offices and Welfare facilities. It should be noted that the proposed waste facility has an identical vulnerability class to the existing and former industrial use. Table D.2 of PPS25 sets out that all of the above uses are designated as Less Vulnerable uses and are appropriate in Flood Zones 1, 2 and 3a. 1.8 Flood Risk Compatibility (PPS25 Table D.3) Flood Risk Vulnerability Classification (PPS25 Table D.2) Essential Infrastructure Water Compatible Highly Vulnerable More Vulnerable Less Vulnerable Flood Zone (PPS25 Table D.1) Zone 1 Zone 2 Zone 3a Zone 3b S S S S S S Exception Test Required Exception Test Required S S Exception Test Required x S Exception Test Required S x x x S S Key: S Development is appropriate x Development should not be permitted 1.9 Sequential Test and Sequential Approach According to PPS25 the Sequential Test gives preference to locating new development in Flood Zone 1. If there are no reasonably available sites in Flood Zone 1, the flood vulnerability of the proposed development can be taken into account in locating development in Flood Zone 2 and then Flood Zone 3. The Avonmouth / Severnside area lies almost entirely within Flood Zone 3a. 6 Discussion with James Thomas from the LSIDB on 14/04/2009
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 5 PPS25 Flood Risk Assessment October 2009 1.9.1 Sequential Test Study Boundary Over the years there has been extensive development in the Avonmouth area based around port related distribution, industrial and waste facilities; extending northwards with significant areas of land being allocated in development plans for employment purposes within the Bristol Local Plan (1997). The Avonmouth / Severnside area was deemed to form an appropriate boundary within which to apply the Sequential Test. 1.9.2 Waste Core Strategy Status The West of England Partnership : Joint Waste Core Strategy Development Plan : Preferred Options (2008) identified sites suitable for development of strategic waste management facilities. All preferred sites within the Avonmouth / Severnside area were situated within Flood Zone 3, and the Sustainability Appraisal recognised that the region was constrained in terms of areas that are subject to flood risk. The West of England Partnership : Joint Waste Core Strategy : Detailed Site Assessment Report (October 2008) identified the former Sevalco site (ref. DS07) as having the potential for development of a strategic waste management facility. 1.9.3 Sequential Test Summary Evidence gathered from strategic planning documents indicates that there are no alternative, available, appropriate and deliverable sites within the Avonmouth / Severnside area for redevelopment of a strategic waste management facility in a lower risk flood zone. The site may, therefore, be deemed to satisfy the requirements of the Sequential Test as set out within PPS25, subject to ratification by the Local Planning Authority. 1.10 Exception Test Criteria On the basis that the site will be viewed favourably in terms of the Sequential Test, the Exception Test needs to be satisfied for the Less Vulnerable use located within Flood Zone 3a. PPS25 describes the Exception Test as providing a method of managing flood risk while still allowing necessary development to occur and will be satisfied where: a) the development provides wider sustainability benefits to the community that outweigh flood risk, informed by a Strategic Flood Risk Assessment (SFRA) where one has been prepared; b) the development should be on developable previously developed land or, if it is not on previously developed land, that there are no reasonable alternative sites on developable previously developed land; and c) a FRA must demonstrate that the development will be safe, without increasing flood risk elsewhere, and, where possible will reduce flood risk overall.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 6 PPS25 Flood Risk Assessment October 2009 Summary Development proposals for a resource recovery centre will contribute to a low carbon economy where waste materials that cannot be used for reprocessing and recycling will be utilised for the generation of renewable energy through the recovery of energy from waste. Proposals can therefore be deemed to satisfy criteria a). The site is on previously developed brownfield land, therefore criteria b) is readily satisfied. This technical assessment of flood risk seeks to demonstrate that criteria c) of the Exception Test can be satisfied.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 7 PPS25 Flood Risk Assessment October 2009 2.0 SOURCES OF INFORMATION 2.1 Flood Zone Map and Flood Defence Data Information regarding the current flood risk at the application site and local flood defences has been obtained from the EA website 7 and confirmed through direct contact with staff at the EA s Bridgwater office and the LSIDB. Refer to Appendix D. 2.2 Historic Flooding As part of this assessment, flooding history in the vicinity of the site was discussed with the EA and the LSIDB. The EA has confirmed that they do not hold any records of historic flooding at or within close proximity of the site. Refer to Appendix D. Based upon a search of the Hydrochronology database compiled by the University of Dundee, together with a brief search using recognised Internet search engines, there would appear to be no history of flooding at the development site itself. 2.3 Strategic Flood Risk Assessment The Lower Severn Internal Drainage Board published the Severnside and Avonmouth Strategic Flood Risk Assessment (SFRA) in January 2008. The SFRA highlights that the area is very susceptible to tidal surge and tidal flooding from overtopping of the tidal defences and that this is the most serious type of flooding when compared with fluvial flooding (which could occur when the Rhines are full) and overland flow. Tidal influences clearly dominate fluvial flood risks at this location. The SFRA provides graphical data which predicts the areas at risk of tidal and/or fluvial flooding and the significance of the flood risk. This data has been analysed within Sections 3.7 and 3.8. 2.4 Topographical Data Topographical Survey data has been provided by. The site elevation typically ranges between 6.2 and 6.7mAOD (refer to Appendix E). The surrounding area is predominantly flat with no significant topographic changes 8. 2.5 Geological Data Geological data was derived from a review of the British Geological Survey Sheet 264-Bristol (1:50,000 Scale) Solid and Drift geology, 2004. Further geological data was obtained from the ground investigation undertaken in June 2009. 7 http://www.environment-agency.gov.uk/maps 8 Consulting Ltd, Avonmouth Due Diligence Land Quality Assessment, Ref.: 416-0036-00353 (May 2008)
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 8 PPS25 Flood Risk Assessment October 2009 3.0 FLOOD RISK ASSESSMENT 3.1 Flood Risk Assessment Methodology & Objectives It is recognised that developments that are designed without regard to flood risk may endanger lives, damage property, cause disruption to the wider community, damage the environment, be difficult to insure and require additional expense on remedial works. Current guidance on development and flood risk 9 identifies several key aims for a development to ensure that it is sustainable in flood risk terms. These aims are as follows: the development should not be at a significant risk of flooding and should not be susceptible to damage due to flooding; the development should not be exposed to flood risk such that the health, safety and welfare of the users of the development, or the population elsewhere, are threatened; normal operation of the development should not be susceptible to disruption as a result of flooding; safe access to and from the development should be possible during flood events; the development should not increase flood risk elsewhere; the development should not prevent safe maintenance of watercourses or maintenance and operation of flood defences; the development should not be associated with an onerous or difficult operation and maintenance regime to manage flood risk. The responsibility for any operation and maintenance required should be clearly defined; future users of the development should be made aware of any flood risk issues relating to the development; the development design should be such that future users will not have difficulty obtaining insurance or mortgage finance, or in selling all or part of the development, as a result of flood risk issues; the development should not lead to degradation of the environment; and the development should meet all of the above criteria for its entire lifetime, including consideration of the potential effects of climate change. This Flood Risk Assessment is undertaken with due consideration of these sustainability aims, and has been prepared to inform the proposed scheme. 9 CIRIA, 2004, Funders Report CP/102 Development and Flood Risk Guidance for the Construction Industry.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 9 PPS25 Flood Risk Assessment October 2009 3.2 Project Scope In order to achieve the aims outlined above, a staged approach has been adopted in undertaking this Flood Risk Assessment, in accordance with current best-practice guidance. A screening study has initially been undertaken to identify whether there are any potential sources of flooding at the site which may warrant further consideration. Any potential flooding issues identified in the screening study have subsequently been considered in a scoping study. The aim of the scoping study is to review all available information and provide a qualitative assessment of the flood risk to the site and the impact of the site on flood risk elsewhere. The report has been undertaken with due regard to the EA s National Standing Advice on Development and Flood Risk 10. 3.3 Screening Study All potential sources of flooding must be considered for any proposed development. A summary of the potential sources of flooding and a review of the potential risk posed by each source at the application site is presented in Table 3. Table 3: Potential Risk Posed by Flooding Sources Potential Source Fluvial flooding Tidal flooding Flooding from rising / high groundwater Overland flow flooding Flooding from artificial drainage systems Flooding due to infrastructure failure Potential Flood Risk at Application Site? Yes Yes Yes (minor) Yes (minor) No Yes 3.4 Scoping Study Following the screening study, additional information has been gathered in order for an experienced Hydrologist to further assess the flood risk at site. A site visit was also undertaken in April 2009. Photographs taken during the site visit are presented in Appendix A. 3.5 Flood Levels The EA provided (refer to Appendix D) the following modelled tidal levels for the River Severn at the seaward face of the defences, parallel to the site: 0.5% annual probability (1:200 year) tidal: 9.12m AOD 0.5% annual probability (1:200 year) tidal + climate change: 9.51m AOD 10 Environment Agency, February 2008, National Standing Advice to Local Planning Authorities for Planning Applications Development and Flood Risk.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 10 PPS25 Flood Risk Assessment October 2009 3.6 Existing Flood Defences The site benefits from the presence of the formal flood defences which are located adjacent to the Severn Estuary. The EA have confirmed that the defences adjacent to the Severn Estuary within the vicinity of the site comprise raised earth embankments with crest heights ranging between 9.10m AOD and 10.8m AOD which provide between a 100 year and 200 year standard of protection to land adjacent to the defences. Refer to Appendix D. It should be noted that EA assessments of standard of protection take into account significant provision for freeboard, where freeboard is defined as the vertical difference between crest level of the flood defence and seaward tidal water level. Typical freeboard allowances for earth embankments are 900mm, therefore the assessed standard of protection would be based upon a lower crest level of between 8.20m AOD 9.90m AOD. 3.7 Technical Assessment of Flood Risk 3.7.1 Tidal Flooding Based upon the EA s Flood Zone Map (refer to Appendix D) the entire site is located within Flood Zone 3 which represents an annual probability of greater than 0.5% of a tidal flood occurring in any one year, although the site is defended to a 100 year standard of protection. The risk and extent of tidal floodwater overtopping the existing defences is predicted to increase over the predicted lifetime of the development taking into account the impact of climate change. The site is located within the SFRA s Defended, Future, Tidal Actual Risk Zone 3 (refer to Figure 7.2 within the SFRA) which represents an annual probability of greater than 0.5% of a tidal flood occurring in any one year taking into account the impact of climate change and the presence of formal flood defences. Refer to Appendix F. The majority of the site lies below the predicted tidal flood levels along the River Severn, thus the site has a significant residual risk from breach (failure) of the existing flood defences coincident with significant tidal conditions along the Severn. The residual risk from breach of the existing flood defences is assessed in Section 3.8. Guidance tables (See Figures 2 and 3) provided within FRA Guidance for New Development Phase 2 11 offer a simple means of assessing the danger to people from flooding in a defended area for the following two scenarios: Overtopping the hazard is related to the distance from defence and the water level above the crest of the defence Breaching hazard is related to the distance from defence and the water level above the floodplain 11 R&D Technical Report FD2320 - FRA Guidance for New Development Phase 2 (October 2005)
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 11 PPS25 Flood Risk Assessment October 2009 The groups of people which are considered to fall in the various danger classes can be considered as follows: Danger for some includes children, the elderly, the infirm Danger for most the general public Danger for all the emergency services The site is located approximately 850m from the defences. Based upon a 0.5 0.99m head above the crest of the defence, overtopping of the defences is deemed to pose a danger to some (see Figure 2 below). Figure 2: Danger to people from overtopping relative to distance from defence The site is typically elevated between 6.2mAOD and 6.7mAOD. The 0.5% annual probability flood level (incorporating an allowance for climate change) at the tidal defences along the Severn Estuary is 9.51mAOD. Based upon a 3m head of floodwater above the floodplain at the tidal defences, with the site being a distance of 850m from the breach of the defences, the hazard is deemed to lie on the cusp of danger for all and danger for most (see Figure 3 below). Figure 3: Danger to people from breaching relative to distance from defence
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 12 PPS25 Flood Risk Assessment October 2009 3.7.2 Wave Action Wave action impacts along the River Severn would increase localised overtopping rates adjacent to the defences, but would not have a tangible effect at the site due to its location approximately 850m inland. Wave action allowances were incorporated within tidal breach modelling analyses undertaken as part of the SFRA as the study area extended to land adjacent to the tidal defences. 3.7.3 Fluvial Flooding Based upon the EA s Flood Zone Maps (refer to Appendix D) the entire site is located within Flood Zone 3 which represents an annual probability of greater than 1% of a flood occurring in any one year without taking into account the presence of flood defences. The vast majority of the site is shown to be located in the SFRA s Fluvial Actual Risk Zone 3 (refer to Figure 7.3 within the SFRA) which represents an annual probability of greater than 1% of a fluvial flood occurring in any one year taking into account the impact of climate change and the presence of formal flood defences. Refer to Appendix F. Fluvial flooding would appear to relate to overtopping of the drain which runs around the eastern, southern borders of the site. The drain is part of a historic system of Rhines which drain the low lying land behind the Severn flood defences. The tidal influence of the downstream River Severn may exacerbate conditions onsite by tidelocking the fluvial network during significant fluvial flood events. 3.7.4 Failure of Infrastructure Failure (shutting) of the Rhine outlet flap valves at New Pill and Stup Pill during fluvial conditions or failure (opening) of the flap valves during tidal conditions could exacerbate conditions onsite. The blockage of culverts could result in localised flooding issues. Should any pumps which control the drainage within the area become blocked or fail (e.g. due to power failure) during fluvial conditions then floodwater could overtop the drains running adjacent to the site leading to out of bank flows onsite. However, failure by one of the above three scenarios at one location would not necessarily pose a risk to the site as excess floodwater would tend to be diverted to an alternative outfall due to the extremely flat local topography, or progress across the extensive areas of lowlying land within the Crooks Marsh flood cell. 3.7.5 Overland Flow The site and surrounding area is relatively flat, therefore overland flow from off site areas is not deemed to pose a significant flood risk to the site. Risks are deemed to be secondary when compared to the tidal and fluvial flood risk.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 13 PPS25 Flood Risk Assessment October 2009 3.7.6 Groundwater Flooding Regional groundwater levels vary in this area but are typically shallow, with the presence of relatively impermeable soils preventing the upward migration of groundwater at this location and any risk would be secondary when compared to the tidal and fluvial flood risk. 3.7.7 Sewer and Water Main Flooding Wessex Water have confirmed that they do not hold any records of public sewer flooding within the vicinity of the site 12. Refer to Appendix G. 3.7.8 Offsite Impact: Floodplain Storage Displacement LSIDB and EA do not consider 13 any area behind the flood defences on the River Severn to be designated as functional floodplain. Therefore, no functional floodplain storage is displaced as a result of the proposed development. Due to the vast area of low lying land adjacent to the River Severn, any loss in tidal flood storage is deemed to pose a negligible risk to offsite areas. Therefore, in line with PPS25 guidance on sites within tidal risk areas, no formal tidal flood storage compensation is required. Nominal volumes of fluvial flood storage could potentially be displaced as a result of the proposals. Impacts will be assessed as part of a fluvial flood modelling analyses to be undertaken by the LSIDB, and mitigation measures provided as part of a holistic surface water and fluvial flood risk management strategy to be formulated in partnership with the LSIDB. Refer to Section 4.9. 3.7.9 Offsite Impact: Surface Water Runoff The total impermeable area of the existing site has been calculated to be approximately 4.4ha using survey data and aerial photography. This equates to approximately 53% of the overall site area. The rest of the site comprises grass and overgrown areas containing shrubs and trees. Total impermeable area coverage for the proposed site has been estimated to be approximately 7.7ha, i.e. approximately 92% of the overall site area. In accordance with paragraph F10 of PPS25, post development runoff rates should be restricted to those rates generated by the pre-developed site, or less, for up to and including the critical 1% annual probability storm event taking into account the impacts of climate change (applied as a 20% uplift in peak rainfall intensity) for the lifetime of the development (in this instance assessed as being 60 years). However, discussions with the LSIDB have highlighted the potential to manage surface water runoff by way of the following principles (refer to Appendix B): 12 Telephone conversation with Debra Wroe, Wessex Water Operations, 17 th December 2008 13 Discussions with James Thomas from the IDB on 14/04/2009
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 14 PPS25 Flood Risk Assessment October 2009 LSIDB Principles No restriction on the discharge of surface water to the rhine system will be stipulated by the LSIDB provided that free discharge can be guaranteed for return period rainfall and fluvial flood events up to an including a 20% annual probability (1:5 years). However, LSIDB prefer that catchment areas of no more than 1.5-2ha be served by each individual outfall to the rhine network. LSIDB would prefer to see off-line storage arrangements comprising rhines / wet ponds for flood mitigation, with water discharging freely from the site. Excess surface water runoff is typically designed to overflow to storage areas from the proposed connection point along the rhine network for events exceeding the 20% annual probability (1:5 year) storm event (refer to Figure 4 below). Figure 4: Example of LSIDB preferred storage arrangement Where it is not possible to connect the site drainage to the nearest LSIDB managed rhine, the LSIDB will permit the construction of new rhines to allow a connection to be achieved. In the event that it is not feasible to provide the surface water attenuation storage recommended by the LSIDB within the site due to onerous development constraints, an offsite alternative drainage solution (or combination of the two) could be implemented in conjunction with the LSIDB subject to an additional fee levy applied on a per developed hectare basis. The fee levy can be offset by capital costs attributed to the provision of onsite infrastructure, and would take into account the volume and rate of surface water runoff currently draining to the rhine network from the existing site. 3.8 Residual Risk Assessment 3.8.1 SFRA Mapping Review Site Hazard Graphical data presented in Figure 7.4 of the SFRA predicts that the western fringes of the site lie within the bandwidth along the tidal defence that would experience high flood hazard following defence breach (failure) coinciding with significant tidal conditions. Refer to Appendix F. Graphical data presented in Figure 7.5 of the SFRA predicts that flood depths would typically range between 0 and 1.5m within the application site.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 15 PPS25 Flood Risk Assessment October 2009 Graphical data presented in Figure 7.6 of the SFRA shows the application site to predominantly lie within the danger for most DEFRA Flood Hazard Category, in the unlikely event of a tidal defence breach. Flood Hazard = Flood Depth x (Flood Velocity + 0.5). Refer to Figure 5. Figure 5: DEFRA Flood Risks to People Flood Hazard Categories Safe Access Route Hazard Safe access / egress route from site is available via Severn Road heading in a south easterly direction for fluvial and tidal events up to and including the criterion set out within PPS25 as the site is defended. Graphical data presented in Figure 7.5 of the SFRA predicts that flood depths on Severn Road following a breach would typically range between 0.5 and 1m for approximately 900m from the site entrance, with a short stretch of the road affected by flood depths ranging from 1 to 1.5m. After 900m, Severn Road is shown to have flood depths of less than 0.25m. Graphical data presented in Figure 7.6 of the SFRA shows Severn Road to lie within the danger for most DEFRA Flood Hazard Category for approximately 900m from the site entrance. SFRA Combined 0.5% annual probability (1:200 year) Tidal + 1% annual probability (1:100 year) Fluvial - Flood Level Assessment A comparative exercise was undertaken in order to predict the flood level within the vicinity of the site for the combined 0.5% annual probability tidal + 1% annual probability fluvial flood event. The flood extents and flood depths shown in Figure 7.5 were compared with detailed topographical survey data and OS mapping. The resultant inland post-breach flood level was assessed to be 7.2mAOD.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 16 PPS25 Flood Risk Assessment October 2009 3.8.2 Flood Defence Breach Analysis Notch weir spreadsheet calculations have been undertaken to estimate the rate of ingress of floodwater into a defined flood cell in the Crooks Marsh area from a breach in the tidal flood defences coinciding with a 0.5% annual probability tidal flood event (with and without incorporation of an allowance for climate change) over two tidal cycles. Refer to summary calculations presented in Appendix H. In line with EA tidal breach trials guidelines, a 50m breach width scenario has been assessed, appropriate for an earth embankment defence at a tidal estuary. Details of the topography of the defined flood cell have been presented in Appendix H. Post-breach landward floodwater levels within the flood cell were predicted to reach the following levels over a duration of 24 hours (2 tidal cycles): 6.66m AOD (0.5% annual probability tidal event) 6.85m AOD (0.5% annual probability tidal event + climate change) 3.8.3 Detailed Flood Hazard Analysis Site Hazard The topographical survey data shows that site levels typically range between 6.2 and 6.7mAOD. Therefore, flood depths onsite would be expected to range between 0 and 0.5m during a tidal breach and between 0.5 and 1m during a combined 0.5% annual probability tidal + 1% annual probability fluvial flood event. Safe Access Route Hazard The topographical survey data shows Severn Road to typically be elevated at between 6.4 and 6.6mAOD adjacent to site, however, the road comprises some localised low sections adjacent to site with a minimum elevation of approximately 6.1mAOD. OS mapping shows Severn Road to be elevated at 6mAOD approximately 185m east of the site which relates to the short stretch of road which is shown on the hazard mapping to suffer flood depths of between 1 and 1.5m. Flood depths on Severn Road adjacent to the site would therefore be expected to typically range between 0.1 and 0.3m during a tidal breach and 0.6 and 0.8m during a combined tidal and fluvial event with short sections of the road potentially having flood depths of up to 0.6m during a tidal breach and 1.1m during a combined tidal and fluvial event. Flood depths are expected to reach 0.7m during a tidal breach and 1.2m during a combined tidal and fluvial event within the stretch of road, east of the site, which is elevated at approximately 6mAOD. Safe access / egress may be afforded to site occupants (following a breach) for a period of approximately 5 hours following a breach (based upon consideration of a post breach water level of 6.4m AOD being deemed to be safe at the low spot along Severn Road).
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 17 PPS25 Flood Risk Assessment October 2009 4.0 PROPOSED MITIGATION MEASURES The following measures have been taken into account during evolution of the development proposals in order to manage flood risks at the site. 4.1 Siting of Built development No sleeping accommodation to be provided on site. Proposals shall comprise no basement areas. 4.2 Finished Floor Levels 4.2.1 Safety of Site Personnel Safe refuge and welfare facilities for all site occupants will be provided within the upper floors of both the proposed MRF and EfW buildings at or above 10.1m AOD (i.e. at or above the future 0.5% annual probability tidal flood level, incorporating climate change, with a 600mm allowance for freeboard. Storey heights are proposed to be 3.6m therefore, in practice, upper floor levels within the MRF and EfW are likely to exceed 11.4m AOD. 4.2.2 Critical Infrastructure Critical infrastructure (that must remain operational at all times) including the electrical plant and switch gear, and control centre is proposed to be set at a minimum elevation of 9.8m AOD (i.e. at 1 st floor level or raised on plinths within the building envelope) to provide an enhanced freeboard allowance of 300mm above the 0.5% annual probability tidal flood level at the defences, incorporating climate change allowances. 4.2.3 Vulnerable Infrastructure In order to minimise the disruption to the operation of the site and limit the damage of key equipment that would require a significant lead time to manufacture replacement plant it is proposed that the steam turbines be situated at or above 9.8mAOD where practical considerations allow. Allowance has been made within the proposed building roof heights for steam turbines to be situated at or above 9.8m AOD. During the design stage the steam turbines may be situated at a lower elevation provided that they are located within a section of the proposed building that can be adequately defended (by hydrostatically resistant walling having a minimum crest height of 9.8m AOD). 4.2.4 Less Vulnerable Infrastructure Other less vulnerable operational plant within the MRF and EfW (e.g. conveyer) are unable to be elevated significantly due to practical considerations (e.g. they must be readily accessible from ground floor slab level by vehicles and operatives). Therefore, it is proposed to install the operational plant between 0.5m and 1m above the ground floor slab on plinths (i.e. at a level of between 8.3m AOD and 8.8m AOD). This will allow excess floodwater to flow beneath the plant during extreme conditions. It is envisaged that the proposed bunker be protected by a raised perimeter wall which would provide an enhanced degree of flood protection.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 18 PPS25 Flood Risk Assessment October 2009 The MRF, offices, frequently manned areas, and other remaining operational areas associated with the EfW are proposed to be set at a minimum elevation of 7.8m AOD to provide a freeboard allowance of 600mm above the for the combined 0.5% annual probability tidal + 1% annual probability fluvial flood level (7.2m AOD as assessed from the Avonmouth / Severnside SFRA). The weighbridge control and associated office will be located at ground slab level (i.e. 7.8m AOD) as this will only be operational when the site is operational and delivery vehicles are able to access the site (i.e. not during extreme flood conditions). Storage / tipping areas and external hardstanding areas should be set at or above existing ground levels (i.e. at ~ 6.8m AOD) to provide flood mitigation from fluvial sources. Facilities should be provided for openings to the storage areas to be caged or gated where possible in order to allow floodwater in to the storage areas during extreme flood conditions, but hindering the outward progress of debris. External landscape and undeveloped areas should remain at, or preferably below existing ground levels to help minimise displacement of flood storage and provide an increase in potential flood storage wherever possible, although depth of excavation is limited due to the presence of a shallow underlying groundwater table. 4.3 Flood Warning System and Evacuation Plan The site is adequately defended from tidal flooding, however, the aim will be to ensure that the site users and workers will have sufficient warning and notice prior to any flood event inundating the site, including a breach (failure) of the tidal defences. A further objective would be to allow sufficient time for a planned shutdown of parts of the facility prior to the onset of flooding. The proposed mitigation put forward is as follows. It is proposed that Viridor Waste Management sign up to the Environment Agency Flood Warnings Direct Service. This will help to act as an early warning system. These proposals are in line with the Defra / Environment Agency document entitled Flood Warning Dissemination Technologies. In addition, a Flood Evacuation Plan should be drawn up for the proposed development site in consultation with the EA and Emergency Services and Emergency Planning Department at Bristol City Council. This is likely to focus on providing a warning when tidal levels are expected to rise above the proposed site elevation of circa 7.8m AOD (albeit tidal water levels will be adequately defended by the presence of the tidal flood defence arrangements for all but the most exceptional circumstances). Based upon breach calculations undertaken for the local flood cell it can be demonstrated that for a full height 50m breach in the tidal defences, it would take approximately 15-17 hours for the flood cell to become inundated to a level of 6.66m AOD, allowing sufficient time for evacuation of site occupants or for relocation to safe refuge areas. 4.4 Safe Refuge In the unlikely event that advance flood warnings are not heeded, or a breach (failure) of the tidal defences were to occur, safe refuge would be afforded to site users within both the MRF and EfW facilities, with internal access being provided to welfare facilities and offices situated on upper floors.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 19 PPS25 Flood Risk Assessment October 2009 Due to the potentially hazardous depths of floodwater generated by a breach in the flood defences, and the lack of advance warning offered by such an event: Safe refuge for all site occupants will be provided within the upper floors of both the proposed MRF and EfW buildings at or above 10.1m AOD (i.e. at or above the future 0.5% annual probability tidal flood level, incorporating climate change, with a 600mm allowance for freeboard. Storey heights are proposed to be 3.6m therefore, in practice, upper floor levels within the MRF and EfW are likely to exceed 11.4m AOD. 4.5 Safe Route of Access / Egress The access / egress route from site involves exiting the site from the south onto Severn Road, heading south easterly for approximately 900m through flood depths ranging between 0.5 and 1.5m (refer to Section 3.8). Vehicles could then continue on Severn Road through flood depths of less than 0.25m over the M49 towards Hallen before continuing on Hallen Road beneath the M5 and then following the B4057 into Bristol. 4.6 Flood Resilience Due to the residual risk of flooding from a breach (failure) of the flood defences coinciding with a significant tidal event, dry and wet proofing works should be incorporated within the development where practical considerations allow. Flood resilience should be built into the development by implementing suitable flood proofing methods to a level of at least 8.4m AOD (i.e. approximately 600mm above finished floor level / formation level, and significantly higher than predicted post breach inland water levels. Service ducts in or below the base slab should be sealed to prevent the ingress of floodwater. 4.7 Hydrostatic Pressure Resistance To assess the durability and robustness of the proposed development, hydro-static and hydro-dynamic calculations should be undertaken by a qualified Structural Engineer in conjunction with a qualified hydrologist to establish the external forces the proposed buildings would have to withstand in the event of a flood defence breach. Predicted velocities of floodwater can be gleaned from hazard mapping provided as part of the SFRA. Structural loadings fall outside the remit of a FRA and should be addressed by way of a planning condition at the design stage, however, inherent mitigation would be built into the fabric of the main building structure, in the form of hydrostatic resistant design techniques, to reduce the impact of moving floodwater upon the operational site. 4.8 Maintaining Site Operations Continuous site operations should be maintainable as a result of implementation of proposed elevated development formation levels, and flood resilience. Provision will be made within the emergency evacuation plan for controlled shutdown of the facility.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 20 PPS25 Flood Risk Assessment October 2009 4.9 Flood Storage Compensation Nominal volumes of fluvial flood storage could potentially be displaced as a result of the proposals. Impacts will be assessed as part of a fluvial flood modelling analyses to be undertaken by the LSIDB. In the event that any fluvial flood storage is displaced as a result of the proposals then flood storage compensation will be provided on a like-for-like (volumetric) or level-for-level basis as part of a holistic surface water and fluvial flood risk management strategy to be formulated in partnership with the LSIDB. 4.10 Site Drainage - Application of Sustainable Drainage Systems Current guidance promotes sustainable water management through the use of Sustainable Drainage Systems (SuDS). A hierarchy of techniques is identified below: Figure 6 SuDS Management Train (from CIRIA Report C697) 1. Prevention the use of good site design and housekeeping measures on individual sites to prevent runoff and pollution (e.g. minimise areas of hard standing). 2. Source Control control of runoff at or very near its source (such as the use of rainwater harvesting). 3. Site Control management of water from several sub-catchments (including routing water from roofs and car parks to one/several large soakaways for the whole site). 4. Regional Control management of runoff from several sites, typically in a retention pond or wetland.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 21 PPS25 Flood Risk Assessment October 2009 It is generally accepted that the implementation of SuDS as opposed to conventional drainage systems, provides several benefits by: Reducing peak flows to watercourses or sewers and potentially reducing the risk of flooding downstream; Reducing the volumes and frequency of water flowing directly to watercourses or sewers from developed sites; Improving water quality over conventional surface water sewers by removing pollutants from diffuse pollutant sources; Reducing potable water demand through rainwater harvesting; Improving amenity through the provision of public open spaces and wildlife habitat; and Replicating natural drainage patterns, including the recharge of groundwater so that base flows are maintained. 4.10.1 Constraints to the use of SuDS Underlying groundwater is known to have been encountered at shallow depths, therefore, the widespread use of infiltration techniques is deemed unviable within the application site.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 22 PPS25 Flood Risk Assessment October 2009 4.10.2 Proposed SuDS Design Statement During the evolution of the proposals, the scheme designers have fully investigated the viability and usage of alternative forms of SuDS. A hierarchy for SuDS, reflecting the degree of sustainability offered by the various SuDS application is shown in Table 4 below. Table 4: SuDS Sustainability Hierarchy Most Sustainable SUDS technique Flood Reduction Water Quality Improvement Landscape & Wildlife Benefit Living roofs Basins and ponds Filter strips and swales Infiltration devices Permeable surfaces and filter drains Least Sustainable Rainwater Harvesting Tanked systems In order to provide a degree of post development benefit, the following SuDS measures are proposed to be incorporated within the development scheme: Surface water attenuation ponds (incorporating permanent water for fire suppression in the event of fire on site) form an integral part of the green infrastructure and will comprise marginal planting and reedbeds where practicable. Ponds will be designed as part of a holistic surface water and fluvial flood risk management strategy to be formulated in partnership with the Lower Severn Internal Drainage Board to protect the EfW facility for up to and including the 1% annual probability storm event (incorporating an allowance for climate change), to allow controlled release of runoff into the local watercourses. Extension of the local rhine network into the site to effectively create new linear swales forming part of the green infrastructure. The SRRRC is designed with a sustainable drainage management scheme. It reuses rainwater following collection in tanks within the building envelope for use in the process plant. Excess harvested water could also be re-used for irrigation of landscape areas.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 23 PPS25 Flood Risk Assessment October 2009 5.0 SUMMARY AND CONCLUSIONS Based upon the EA s Flood Zone Mapping and technical assessment, the site is located entirely in Flood Zone 3a which represents an annual probability of greater than 0.5% of a tidal flood occurring in any one year. The site is deemed to meet Sequential Test criteria due to a lack of alternative sites at lower risk of flooding, and direction from Joint Waste Core Strategy. Evidence gathered from strategic planning documents indicates that there are no alternative, available, appropriate and deliverable sites within the Avonmouth / Severnside area for redevelopment of a strategic waste management facility in a lower risk flood zone. The Joint Waste Core Strategy identified the former Selvaco site as having the potential for development of a strategic waste management facility. The site is therefore, deemed to satisfy the requirements of the Sequential Test. The site is defended from the tidal River Severn to between 1:100 and 1:200 year standard. Safe access / egress routes from the site are available via Severn Road heading in a south easterly direction for fluvial and tidal events up to and including the criterion set out within PPS25 as the site is adequately defended. The primary risk of flooding associated with the site is fluvial, associated with out-of-bank flows from the local rhine network, risks which may be exacerbated by tide-locking of the rhine outfalls to the Severn Estuary during tidal flood conditions. However, the greatest flood consequence would result from residual risk scenarios, i.e. breach (failure) of tidal defences coinciding with significant tidal conditions. It is proposed to manage the risk by elevating formation level of the facility, and critical and vulnerable infrastructure within the facility wherever practical to do so, by providing safe refuge within buildings, and by implementation of robust flood warning measures linked to tidal conditions and an evacuation plan. Safe access / egress may be afforded to site occupants for a period of approximately 5 hours following a tidal defence breach (based upon consideration of a post breach water level of 6.4m AOD being deemed to be safe at the low spot along Severn Road). Based upon breach calculations undertaken for the local flood cell it can be demonstrated that for a full height 50m breach in the tidal defences, it would take approximately 15-17 hours for the flood cell to become inundated to a level of 6.66m AOD (approximately existing site level), allowing sufficient time for evacuation of site occupants or for relocation to proposed safe refuge areas. The site falls within Lower Severn Internal Drainage Board (LSIDB) jurisdiction in terms of the planning consultation process on flood risk and surface water management. Surface water management facilities will be designed to limit off-site runoff rates to those generated by the existing brownfield site, or less, in line with paragraph F10 of PPS25, or to rates to be agreed with the LSIDB.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 24 PPS25 Flood Risk Assessment October 2009 Extensive SuDS provision will manage and control surface water runoff, taking the form of surface water attenuation ponds (incorporating permanent water for fire suppression in the event of fire on site) forming an integral part of the green infrastructure, and will comprise marginal planting and reedbeds where practicable. Ponds will be designed as part of a holistic surface water and fluvial flood risk management strategy to be formulated in partnership with the Lower Severn Internal Drainage Board to protect the EfW facility for up to and including the 1% annual probability storm event (incorporating an allowance for climate change), to allow controlled release of runoff into the local watercourses. SuDS will be provided in the form of open surface water attenuation ponds, swales (by extending the rhine network into the site), and rainwater harvesting facilities. Impacts of any displaced fluvial flood storage, and of any excess surface water runoff generated as a result of the proposals, will be assessed as part of a fluvial flood modelling analyses to be undertaken by the LSIDB, and mitigation measures provided as part of a holistic surface water and fluvial flood risk management strategy to be formulated in partnership with the LSIDB. This Flood Risk Assessment, forming part of the Environmental Statement accompanying the planning submission, demonstrates that Part c) of the Exception Test may be satisfied with the implementation of reasonable, deliverable flood management and mitigation measures.
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 25 PPS25 Flood Risk Assessment September 2009 APPENDIX A SITE LOCATION PLAN & SITE PHOTOGRAPHS
Photograph 1: View north-west through derelict plant Photograph 2: View north of existing Warehouse
Photograph 3: View of southern boundary in the south-east of the site Photograph 4: Buildings in the west of the site
Photograph 5: View south of southern boundary Photograph 6: View east of Storage Tank and Warehouse
Photograph 7: View north of northern boundary Photograph 8: View south of Warehouse
Photograph 9: View of the south east corner of site
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 26 PPS25 Flood Risk Assessment September 2009 APPENDIX B LOWER SEVERN INTERNAL DRAINAGE BOARD WATERCOURSE PLAN & IDB CORRESPONDENCE
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 27 PPS25 Flood Risk Assessment September 2009 APPENDIX C DEVELOPMENT PROPOSALS
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 28 PPS25 Flood Risk Assessment September 2009 APPENDIX D ENVIRONMENT AGENCY FLOOD ZONE MAP & EA CORRESPONDENCE
CSC\27443 Crooks Marsh, Avonmouth Legend Main River Flood Zone 2 Flood Zone 3 Approx NGR ST 53777 81794 Date: 19 December 2008 RR Crown copyright. All rights reserved. Environment Agency, 100026380, 2004. This map is based on Ordnance Survey Landline data and produced for the Environment Agency with the permission of Ordnance Survey. Aerial imagery is copyright Getmapping plc, all rights reserved. Licence number 22047.
Mr William Legg Consulting Limited wlegg@slrconsulting.com Our ref: Your ref: NWX/CSC/27443 Date: 7 January 2009 Dear Mr Legg Information request Avonmouth, Bristol Thank you for your enquiry of 19 December 2008. We are happy to provide the following information: We do not own the model Strategic Flood Risk Assessment study of the Avonmouth to Severnside area, January 2007 however it is available from Bristol City Council s website at: The Strategic Flood Risk Assessment Avonmouth/Severnside Summary Report (Capita Symonds, January 2007) http://www.bristol.gov.uk/ccm/content/environment-planning/planning/ planning-policydocuments/bristol-development-framework/evidence-base-fsis/avonmouth-severnside-sfra.en). Please note that it includes the flood depths and hazard rating maps. The Flood Map indicates that the property is within Flood Zone 3. For your information enclosed is a Flood Map which indicates the estimated extent of flooding from the river which may occur from an extreme rainfall event. Zone 1 - is shaded white and shows areas with the lowest probability of flooding from rivers and the sea, where the chance of flooding in any one year is less than 0.1% (i.e. a 1000 to 1 chance). The Environment Agency Rivers House, East Quay, Bridgwater, Somerset TA6 4YS Tel: 08708 506506 Fax: 01278 452985 DX 135476 Bridgwater 3 Email: enquiries@environment-agency.gov.uk www.environment-agency.gov.uk
Zone 2 - is shaded turquoise and shows the area between Zone 1 and Zone 3. This represents an area with the chance of flooding in any one year between 0.1% and 1% fluvial or 0.5% tidal (i.e. between a 1000 to 1 and a 100 to 1 fluvial or 200 to 1 tidal chance). The outer edge of this zone is referred to as the Extreme Flood Outline (EFO). Zone 3 - is shaded blue and shows areas with the highest probability of flooding. The chance of flooding in any one year is greater than or equal to 1% (i.e. a 100 to 1 chance) for river flooding and greater or equal to 0.5% (i.e. a 200 to 1 chance) for coastal and tidal flooding. The data for the flood defences will follow in due course. We hope you find this information helpful and it is provided subject to the notice overleaf, which we strongly recommend you read. Yours sincerely NATASHA TURNER External Relations Officer Enc: Standard Notice, Commercial The Environment Agency Rivers House, East Quay, Bridgwater, Somerset TA6 4YS Tel: 08708 506506 Fax: 01278 452985 DX 135476 Bridgwater 3 Email: enquiries@environment-agency.gov.uk www.environment-agency.gov.uk
Page 1 of 1 William Legg From: Remiszewski, Richard [richard.remiszewski@environment-agency.gov.uk] Sent: 09 April 2009 10:38 To: William Legg Cc: SW Wessex North, External Relations Subject: CSC\27433 Avonmouth Attachments: Environment Agency Standard Notice - Commercial.doc Dear sir, The modelled tidal flood levels are: 1:200 year tidal = 9.12m AOD 1:200 year tidal + climate change = 9.51m AOD Richard Remiszewski Phonetic: REM IS CHEF SKI Flood Risk Mapping & Data Management Flood & Coastal Risk Management - Wessex Direct Dial +44(0)1278 484714 richard.remiszewski@environment-agency.gov.uk Environment Agency Rivers House East Quay Bridgwater Somerset TA6 4YS Please consider the environment - do you really need to print this email Information in this message may be confidential and may be legally privileged. If you have received this message by mistake, please notify the sender immediately, delete it and do not copy it to anyone else. We have checked this email and its attachments for viruses. But you should still check any attachment before opening it. We may have to make this message and any reply to it public if asked to under the Freedom of Information Act, Data Protection Act or for litigation. Email messages and attachments sent to or from any Environment Agency address may also be accessed by someone other than the sender or recipient, for business purposes. If we have sent you information and you wish to use it please read our terms and conditions which you can get by calling us on 08708 506 506. Find out more about the Environment Agency at www.environment-agency.gov.uk 04/09/2009
Mr William Legg Consulting Limited wlegg@slrconsulting.co.uk Our ref: Your ref: NWX/CSC/28076 Date: 22 April 2009 Dear Mr Legg Information request Information on Avonmouth Thank you for your enquiry of 20 April 2009. We are happy to provide the following information: The site lies close to two local authority boundaries. Although our records do not show any specific flood incidents at this location, we advise that you also contact the Drainage Engineer, Mr Chris Brinsdon of Bristol City Council, Brunel House, St Georges Road, Bristol BS1 5UY as he may be able to provide further advice with respect to localised flooding and drainage issues. Bristol City Council The Council House College Green BS1 5TR Tel: 0117 922 2000 - (Switchboard hours 8.30am - 5.00pm Monday to Thursday, 8.30am - 4.30pm Friday) The Environment Agency Rivers House, East Quay, Bridgwater, Somerset TA6 4YS Tel: 08708 506506 Fax: 01278 452985 DX 135476 Bridgwater 3 Email: enquiries@environment-agency.gov.uk www.environment-agency.gov.uk
Again our records do not show any specific flood incidents at this location, we advise that you also contact the Drainage Engineer Mr R Fuller of South Gloucestershire Council, The Elliott Buildings, Broad Lane, Yate, South Gloucestershire, BS37 7ES, as he may be able to provide further advice with respect to localised flooding and drainage issues. WEB PAGE http://www.southglos.gov.uk/nr/exeres/50778897-1f47-43fb-b848-703b722e15a2 EMAIL http//www.southglos.gov.uk We hope you find this information helpful and it is provided subject to the notice overleaf, which we strongly recommend you read. Yours sincerely PAUL KELLY Corporate Serices Assistant Enc: Standard Notice, Non-commercial The Environment Agency Rivers House, East Quay, Bridgwater, Somerset TA6 4YS Tel: 08708 506506 Fax: 01278 452985 DX 135476 Bridgwater 3 Email: enquiries@environment-agency.gov.uk www.environment-agency.gov.uk
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 29 PPS25 Flood Risk Assessment September 2009 APPENDIX E TOPOGRAPHICAL SURVEY
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 30 PPS25 Flood Risk Assessment September 2009 APPENDIX F EXTRACTS FROM AVONMOUTH / SEVERNSIDE STRATEGIC FLOOD RISK ASSESSMENT
Bristol City Council Strategic Flood Risk Assessment South Gloucestershire Council Summary report Lower Severn Drainage Board January 2007 Figure 7.1 Flood Zones 27
Bristol City Council Strategic Flood Risk Assessment South Gloucestershire Council Summary report Lower Severn Drainage Board January 2007 Figure 7.2 Tidal Residual and Actual Risk Flood Extents 28
Bristol City Council Strategic Flood Risk Assessment South Gloucestershire Council Summary report Lower Severn Drainage Board January 2007 Figure 7.3 Fluvial Residual and Actual Risk Flood Extents 29
Bristol City Council Strategic Flood Risk Assessment South Gloucestershire Council Summary report Lower Severn Drainage Board January 2007 Figure 7.4 Breach Hazard Bandwidth 30
Bristol City Council Strategic Flood Risk Assessment South Gloucestershire Council Summary report Lower Severn Drainage Board January 2007 Figure 7.5 Actual Risk Flood Depths 1% AEP River Flooding & 0.5% AEP Coastal Flooding 31
Bristol City Council Strategic Flood Risk Assessment South Gloucestershire Council Summary report Lower Severn Drainage Board January 2007 Figure 7.6 Actual Risk Flood Hazard Category 1% AEP River Flooding & 0.5% AEP Coastal Flooding 32
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 31 PPS25 Flood Risk Assessment September 2009 APPENDIX G WESSEX WATER SEWER & WATER MAIN RECORDS
Severn Road Resource Recovery Centre Ref: 402-0036-00374 Viridor Waste Management 32 PPS25 Flood Risk Assessment September 2009 APPENDIX H FLOOD DEFENCE BREACH ANALYSIS
N LEGEND 6-6.5m AOD Cell W E S 6.5-7m AOD Cell 7-7.5m AOD Cell 8 STOW COURT STOW-CUM-QUY CAMBRIDGE CAMBS CB5 9AS T: 01223 813805 F: 01223 813783 www.slrconsulting.com SEVERN ROAD RESOURCE RECOVERY CENTRE AVONMOUTH FLOOD RISK ASSESSMENT FLOOD CELL EXTENTS DWG No. 1 REPRODUCED BY PERMISSION OF ORDNANCE SURVEY ON BEHALF OF HMSO. CROWN COPYRIGHT AND DATABASE RIGHT OS DATA LICENCE EXPIRATION: 09/06/2010 ALL RIGHTS RESERVED. LICENCE NUMBER AL100012293 Scale NTS Date SEPTEMBER 2009
Job: Severn Road Resource Recovery Centre, Avonmouth - Breach Assessment (incorporating climate change) Tidal Flood Level 9.51 maod MLWN -2.72 maod Difference 12.23 m 1 / 12th 1.02 m Tide Cycle Tidal Level (maod) The tidal level exceeds the breach base (7mAOD) for approximately 213 minutes per cycle. 0-2.72 1-1.70 2 0.34 3 3.40 4 6.45 5 8.49 6 9.51 7 8.49 8 6.45 9 3.40 10 0.34 11-1.70 12-2.72 Flood Cells Hours Cd = 0.544 Q = c d 2/3B (2g) H 3/2 Min elevation (maod) Max elevation (maod) Area (m2) B = 50 m 6 6.5 4078000 Breach Base 7 maod 6.5 7 6450000 7 7.5 10528000
Time which Tidal Level Exceeds 7mAOD (mins) Tidal Level (maod) Htn (m) Q at Htn (m3/s) Ht n+1 (m) Q at Htn+1 (m3/s) Mean Flow (m3/s) tn+1 -tn (s) Volume Change (m3) Total Volume (m3) Flood Depth (m) Flood Level (maod) 1st Cycle 0 7 0 0.000 0.17 5.627 2.81 270 759.65 760 0.000 6.000 4.5 7.17 0.17 5.627 0.6 37.311 21.47 720 15457.56 16217 0.004 6.004 16.5 7.6 0.6 37.311 0.99 79.079 58.19 720 41900.09 58117 0.014 6.014 28.5 7.99 0.99 79.079 1.33 123.135 101.11 720 72797.03 130914 0.032 6.032 40.5 8.33 1.33 123.135 1.63 167.066 145.10 720 104472.39 235387 0.058 6.058 52.5 8.63 1.63 167.066 1.94 216.924 191.99 720 138236.38 373623 0.092 6.092 64.5 8.94 1.94 216.924 2.19 260.179 238.55 720 171757.12 545380 0.134 6.134 76.5 9.19 2.19 260.179 2.39 296.621 278.40 720 200448.07 745828 0.183 6.183 88.5 9.39 2.39 296.621 2.5 317.333 306.98 720 221023.72 966852 0.237 6.237 100.5 9.5 2.5 317.333 2.5 317.333 317.33 720 228480.00 1195332 0.293 6.293 112.5 9.5 2.5 317.333 2.39 296.621 306.98 720 221023.72 1416356 0.347 6.347 124.5 9.39 2.39 296.621 2.19 260.179 278.40 720 200448.07 1616804 0.396 6.396 136.5 9.19 2.19 260.179 1.94 216.924 238.55 720 171757.12 1788561 0.439 6.439 148.5 8.94 1.94 216.924 1.63 167.066 191.99 720 138236.38 1926797 0.472 6.472 160.5 8.63 1.63 167.066 1.33 123.135 145.10 720 104472.39 2031270 0.498 6.498 172.5 8.33 1.33 123.135 0.99 79.079 101.11 720 72797.03 2104067 0.510 6.510 184.5 7.99 0.99 79.079 0.6 37.311 58.19 720 41900.09 2145967 0.517 6.517 196.5 7.6 0.6 37.311 0.17 5.627 21.47 720 15457.56 2161424 0.519 6.519 208.5 7.17 0.17 5.627 0 0.000 2.81 270 759.65 2162184 0.519 6.519 213 7 0 0.000 0 0.000 0.00 0 0.00 2162184 0.519 6.519 2nd Cycle 0 7 0 0.000 0.17 5.627 2.81 270 759.65 2162944 0.519 6.519 4.5 7.17 0.17 5.627 0.6 37.311 21.47 720 15457.56 2178401 0.522 6.522 16.5 7.6 0.6 37.311 0.99 79.079 58.19 720 41900.09 2220301 0.528 6.528 28.5 7.99 0.99 79.079 1.33 123.135 101.11 720 72797.03 2293098 0.539 6.539 40.5 8.33 1.33 123.135 1.63 167.066 145.10 720 104472.39 2397571 0.556 6.556 52.5 8.63 1.63 167.066 1.94 216.924 191.99 720 138236.38 2535807 0.577 6.577 64.5 8.94 1.94 216.924 2.19 260.179 238.55 720 171757.12 2707564 0.604 6.604 76.5 9.19 2.19 260.179 2.39 296.621 278.40 720 200448.07 2908012 0.635 6.635 88.5 9.39 2.39 296.621 2.5 317.333 306.98 720 221023.72 3129036 0.669 6.669 100.5 9.5 2.5 317.333 2.5 317.333 317.33 720 228480.00 3357516 0.704 6.704 112.5 9.5 2.5 317.333 2.39 296.621 306.98 720 221023.72 3578540 0.739 6.739 124.5 9.39 2.39 296.621 2.19 260.179 278.40 720 200448.07 3778988 0.770 6.770 136.5 9.19 2.19 260.179 1.94 216.924 238.55 720 171757.12 3950745 0.796 6.796 148.5 8.94 1.94 216.924 1.63 167.066 191.99 720 138236.38 4088981 0.818 6.818 160.5 8.63 1.63 167.066 1.33 123.135 145.10 720 104472.39 4193454 0.834 6.834 172.5 8.33 1.33 123.135 0.99 79.079 101.11 720 72797.03 4266251 0.845 6.845 184.5 7.99 0.99 79.079 0.6 37.311 58.19 720 41900.09 4308151 0.852 6.852 196.5 7.6 0.6 37.311 0.17 5.627 21.47 720 15457.56 4323608 0.854 6.854 208.5 7.17 0.17 5.627 0 0.000 2.81 270 759.65 4324368 0.854 6.854 213 7 0 0.000 0 0.000 0.00 0 0.00 4324368 0.854 6.854
12 10 8 6 4 2 0-2 -4 Tidal Variation between MLWN and 0.5% annual probability tidal flood level (incorporating an allowance for climate change) 0 2 4 6 8 10 12 Time (Hours) Tidal Level (maod)
Job: Severn Road Resource Recovery Centre, Avonmouth - Breach Assessment Tidal Flood Level 9.12 maod MLWN -2.72 maod Difference 11.84 m 1 / 12th 0.99 m Tide Hours tidal level The tidal level exceeds the breach base (7mAOD) for approximately 197 minutes per cycle. Cycle 0-2.72 1-1.73 2 0.24 3 3.20 4 6.16 5 8.13 6 9.12 7 8.13 8 6.16 9 3.20 10 0.24 11-1.73 12-2.72 Cd = 0.544 Q = c d 2/3B (2g) H 3/2 Min elevation (maod) Flood Cells Max elevation (maod) Area (m2) B = 50 m 6 6.5 4078000 Breach Base 7 maod 6.5 7 6450000 7 7.5 10528000
Time which Tidal Level Exceeds 7mAOD (mins) Tidal Level (maod) Htn (m) Q at Htn (m3/s) Ht n+1 (m) Q at Htn+1 (m3/s) Mean Flow (m3/s) tn+1 -tn (s) Volume Change (m3) Total Vol (m3) Flood Depth (m) 1st Cycle 0 7 0 0.000 0.06 1.180 0.59 144 84.95 85 0.000 6.000 2.4 7.06 0.06 1.180 0.46 25.046 13.11 720 9441.40 9526 0.002 6.002 14.4 7.46 0.46 25.046 0.82 59.611 42.33 720 30476.61 40003 0.010 6.010 26.4 7.82 0.82 59.611 1.13 96.432 78.02 720 56175.66 96179 0.024 6.024 38.4 8.13 1.13 96.432 1.42 135.843 116.14 720 83619.28 179798 0.044 6.044 50.4 8.42 1.42 135.843 1.69 176.374 156.11 720 112398.40 292196 0.072 6.072 62.4 8.69 1.69 176.374 1.91 211.912 194.14 720 139783.16 431979 0.106 6.106 74.4 8.91 1.91 211.912 2.06 237.359 224.64 720 161737.75 593717 0.146 6.146 86.4 9.06 2.06 237.359 2.12 247.805 242.58 720 174659.08 768376 0.188 6.188 98.4 9.12 2.12 247.805 2.06 237.359 242.58 720 174659.08 943035 0.231 6.231 110.4 9.06 2.06 237.359 1.91 211.912 224.64 720 161737.75 1104773 0.271 6.271 122.4 8.91 1.91 211.912 1.69 176.374 194.14 720 139783.16 1244556 0.305 6.305 134.4 8.69 1.69 176.374 1.42 135.843 156.11 720 112398.40 1356955 0.333 6.333 146.4 8.42 1.42 135.843 1.13 96.432 116.14 720 83619.28 1440574 0.353 6.353 158.4 8.13 1.13 96.432 0.82 59.611 78.02 720 56175.66 1496750 0.367 6.367 170.4 7.82 0.82 59.611 0.46 25.046 42.33 720 30476.61 1527226 0.375 6.375 182.4 7.46 0.46 25.046 0.06 1.180 13.11 720 9441.40 1536668 0.377 6.377 194.4 7.06 0.06 1.180 0 0.000 0.59 144 84.95 1536753 0.377 6.377 196.8 7 0 0.000 0 0.000 0.00 0 0.00 1536753 0.377 6.377 2nd Cycle 0 7 0 0.000 0.06 1.180 0.59 144 84.95 1536838 0.377 6.377 2.4 7.06 0.06 1.180 0.46 25.046 13.11 720 9441.40 1546279 0.379 6.379 14.4 7.46 0.46 25.046 0.82 59.611 42.33 720 30476.61 1576756 0.387 6.387 26.4 7.82 0.82 59.611 1.13 96.432 78.02 720 56175.66 1632931 0.400 6.400 38.4 8.13 1.13 96.432 1.42 135.843 116.14 720 83619.28 1716550 0.421 6.421 50.4 8.42 1.42 135.843 1.69 176.374 156.11 720 112398.40 1828949 0.448 6.448 62.4 8.69 1.69 176.374 1.91 211.912 194.14 720 139783.16 1968732 0.483 6.483 74.4 8.91 1.91 211.912 2.06 237.359 224.64 720 161737.75 2130470 0.514 6.514 86.4 9.06 2.06 237.359 2.12 247.805 242.58 720 174659.08 2305129 0.541 6.541 98.4 9.12 2.12 247.805 2.06 237.359 242.58 720 174659.08 2479788 0.568 6.568 110.4 9.06 2.06 237.359 1.91 211.912 224.64 720 161737.75 2641526 0.593 6.593 122.4 8.91 1.91 211.912 1.69 176.374 194.14 720 139783.16 2781309 0.615 6.615 134.4 8.69 1.69 176.374 1.42 135.843 156.11 720 112398.40 2893707 0.633 6.633 146.4 8.42 1.42 135.843 1.13 96.432 116.14 720 83619.28 2977326 0.645 6.645 158.4 8.13 1.13 96.432 0.82 59.611 78.02 720 56175.66 3033502 0.654 6.654 170.4 7.82 0.82 59.611 0.46 25.046 42.33 720 30476.61 3063979 0.659 6.659 182.4 7.46 0.46 25.046 0.06 1.180 13.11 720 9441.40 3073420 0.660 6.660 194.4 7.06 0.06 1.180 0 0.000 0.59 144 84.95 3073505 0.660 6.660 196.8 7 0 0.000 0 0.000 0.00 0 0.00 3073505 0.660 6.660 Flood Level (maod)
10 8 6 4 2 0-2 -4 Tidal Variation between MLWN and 0.5% annual probability tidal flood level 0 2 4 6 8 10 12 Hours (hrs) Tidal Level (maod)
AYLESBURY 7 Wornal Park, Menmarsh Road, Worminghall, Aylesbury, Buckinghamshire HP18 9PH T: 01844 337380 / F: 01844 337381 BATH Westcross House, 73 Midford Road, Bath, Somerset BA2 5RT T: 01225 832832 / F: 01225 834343 BRADFORD-ON-AVON Treenwood House, Rowden Lane, Bradford-on-Avon, Wiltshire BA15 2AU T: 01225 309400 / F: 01225 309401 BRISTOL 109 Pembroke Road, Clifton, Bristol, Avon BS8 3EU T: 0117 906 4280 / F: 0117 317 9535 CAMBRIDGE 8 Stow Court, Stow-cum-Quy, Cambridge, Cambridgeshire CB25 9AS T: 01223 813805 / F: 01223 813783 CARDIFF Fulmar House, Beignon Close, Ocean Way, Cardiff CF24 5HF T: 029 20491010 / F: 029 20487903 CHELMSFORD Unit 77, The Waterhouse Business Centre, 2 Cromer Way, Chelmsford, Essex CM1 2QE T: 01245 392170 / F: 01245 392171 DUBLIN 7 Dundrum Business Park, Windy Arbour, Dublin 14, Ireland T: + 353 (0)1 2964667 / F: + 353 (0)1 2964676 EDINBURGH No. 4 The Roundal, Roddinglaw Business Park, Gogar, Edinburgh EH12 9DB T: 0131 3356830 / F: 0131 3356831 EXETER The Innovation Centre, Rennes Drive, University of Exeter Campus, Exeter EX4 4RN T: 01392 247913 / F: 01392 425246 FARNBOROUGH The Pavilion, 2 Sherbourne Road, South Farnborough, Hampshire GU14 6JT T: 01252 515682 / F: 01252 512274 GLASGOW 4 Woodside Place, Charing Cross, Glasgow G3 7QF T: 0141 3535037 / F: 0141 3535038 HUDDERSFIELD Westleigh House, Wakefield Road, Denby Dale, Huddersfield, West Yorkshire HD8 8QJ T: 01484 860521 / F: 01484 868286 LEEDS Suite 1, Jason House, Kerry Hill, Horsforth, Leeds, West Yorkshire LS18 4JR T: 0113 2580650 / F: 0113 2818832 MAIDSTONE 19 Hollingworth Court, Turkey Mill, Maidstone, Kent ME14 5PP T: 01622 609242 / F: 01622 695872 NEWCASTLE-UPON-TYNE Sailors Bethel, Horatio Street, Newcastleupon-Tyne, Tyne and Wear NE1 2PE T: 0191 2611966 / F: 0191 2302346 NOTTINGHAM Aspect House, Aspect Business Park, Bennerley Road, Nottingham NG6 8WR T: 0115 9647280 / F: 0115 9641576 REDDITCH Brockhill Court, Brockhill Lane, Redditch, Worcestershire B97 6RB T: 01527 597000 / F: 01527 584408 SHREWSBURY Mytton Mill, Forton Heath, Montford Bridge, Shrewsbury, Shropshire SY4 1HA T: 01743 850170 / F: 01743 850868 STAFFORD 8 Parker Court, Staffordshire Technology Park, Beaconside, Stafford, Staffordshire ST18 0WP T: 01785 253331 / F: 01785 246660 WARRINGTON Suite 9 Beech House, Padgate Business Park, Green Lane, Warrington, Cheshire WA1 4JN T: 01925 827218 / F: 01925 827977