Water Q1 (The Quadrant) Boston April Q1 (The Quadrant) Boston Flood Risk Assessment

Transcription

1 Water Q1 (The Quadrant) Boston April 2014 Q1 (The Quadrant) Boston Flood Risk Assessment

2 Prepared by Anna Gee Checked by Matthew Wilson Graduate Flood Risk Consultant Senior Engineer Approved by: Graham Knott Project Director Rev No Comments Checked by Approved by Date 1 Draft for review MW GK 31/03/ Revision following client comments MS CS 30/04/2014 5th Floor, 2 City Walk, Leeds, LS11 9AR Telephone: Website: Reference Tytton Lane FRA Date Created April 2014 This document has been prepared by AECOM Limited for the sole use of our client (the Client ) and in accordance with generally accepted consultancy principles, the budget for fees and the terms of reference agreed between AECOM Limited and the Client. Any information provided by third parties and referred to herein has not been checked or verified by AECOM Limited, unless otherwise expressly stated in the document. No third party may rely upon this document without the prior and express written agreement of AECOM Limited.

3 Table of Contents 1 Introduction Development Site Planning Policy Flood Risk Surface Water Management Flood Risk Mitigation Conclusions... 26

4 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 1 Capabilities on project: Water 1 Introduction 1.1 Terms of Reference AECOM has been commissioned by Chestnut Homes to produce a Flood Risk Assessment (FRA) in support of a hybrid outline and detailed planning application for the development of Q1 (the Quadrant) Boston, Lincolnshire (hereafter referred to as the proposed development site ) The proposed development site is approximately 29 hectares (Ha) in area. The hybrid planning application proposes the following description of the development; Hybrid (part-outline/part-full) planning application for a single composite development comprising: a new Community Stadium for Boston United Football Club (including education, community and sports facilities); a food store (Use Class A1) gross floor area approximately 7,000 sqm together with Petrol Filling Station; in the region of 500 dwellings (Use Class Order C3) offering a mix and range of house types and tenures; commercial and leisure uses (Use Classes A3, A4, A5 with a total gross floor area in the region of 2,200 sqm; a hotel (approximately 60 beds); a new distributor road connecting the A16 with London Road; vehicular, cycle and pedestrian access; associated car/coach parking spaces; and open space/landscape provision A FRA is required as the development site is over 1ha and located entirely within Flood Zone 3a, as defined by the Environment Agency and Boston Strategic Flood Risk Assessment (SFRA), and is therefore at high risk of fluvial or tidal flooding Policy guidance for development and flood risk is part of the wider National Planning Policy Framework (NPPF) and the associated planning practice guidance, published in March 2012 and March 2014 respectively. This FRA considers the development with regard to NPPF and addresses initial flood risk concerns raised by the Environment Agency (EA), Black Sluice Internal Drainage Board (BSIDB) and Boston Borough Council. 1.2 Purpose of Study The assessment is a holistic risk based assessment of potential flooding from all possible sources, including fluvial flooding from adjacent watercourses, tidal flooding from the Wash and tidal Haven, groundwater, surface water runoff, sewer systems and artificial sources. The assessment also identifies and examines the residual flood risk to the development site and neighbouring properties. The aim of this report is primarily to consider flood risk and satisfy requirements under NPPF. This assessment has also been undertaken in accordance with CIRIA C624 Development and Flood Risk Guidance for the Construction Industry (2004) and the NPPF planning practice guidance (2014) To inform the assessment, information has been obtained from the following sources: Site information provided by Signet Planning and Chestnut Homes, including proposed site development master plans dated December 2013; Consultation with Environment Agency (Partnerships & Strategic Overview), Black Sluice IDB and Boston Borough Council; Boston Strategic Flood Risk Assessment (SFRA); River Witham Catchment Flood Management Plan (CFMP); Northern Area Tidal Modelling. Volume 4: Breach Flood Mapping (Environment Agency, 2010); and Tidal Hydraulic Breach Modelling (AECOM 2014).

5 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 2 Capabilities on project: Water 2 Development Site 2.1 Existing Site The development site is located approximately 2km south west of Boston, Lincolnshire, at grid reference TF (Figure 1). The proposed development site is currently agricultural land bordered to the north and south by existing residential dwellings and to the east by further agricultural land. An IDB drain, Wyberton Towns Drain, runs along the southern boundary of the site. The tidally influenced Boston Haven, which provides the outfall for the entire River Witham catchment, flows in a south-easterly direction approximately 2km to the east of the site, before discharging into the North Sea The Boston Strategic Flood Risk Assessment (SFRA) indicates that the Haven is defended along its length to reduce the risk of tidal flooding. Downstream of the Black Sluice and Maud Foster Sluice (approximately 2km north-east of the proposed development site) the defences are primarily earth embankments with extensive toe revetments to minimise tidal scour. Upstream of these sluices hard defences are in place and afford a 0.66% (1 in 150 year) standard of protection. Maintenance of the defences is extensive and includes routine reactive repairs, mechanical and electrical maintenance and frequent revetment replenishment works. The site is also afforded some protection by the flood defences along the Lower River Witham which is located approximately 3.5km north the site The River Witham CFMP states that there is a substantial risk from tidal flooding within this area and that climate change will significantly increase the risk of flooding in Boston. The CFMP recommends that further action be taken in the future to reduce flood risk in both the long and short term The British geological Society (BGS) online map (accessed ) indicated that the site is characterised by mudstone bedrock overlain by superficial alluvium deposits. The site is not shown to be overlying any aquifer. Figure 1. Site location plan showing the proposed development site (in red) in relation to the town of Boston and the tidal Boston Haven.

6 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 3 Capabilities on project: Water 2.2 Development Proposals Chestnut Homes are intending to develop a mixed use site; including residential and commercial parcels (outline planning application) as well as a new BUFC stadium (detailed planning application). The residential area is to comprise approximately 500 N o. houses and will include open space and equipped play areas. Six commercial units are proposed and will include a hotel and restaurants. A food store and petrol filling station are also proposed to the south of this commercial area. The new community stadium will have a 5,000 capacity and is located to the east of the development site It is assumed that a phased approach to the residential and commercial development area will take place, although this has not been confirmed. The community stadium will be constructed whilst the masterplan for the residential and commercial area continues to be developed This FRA is to support the hybrid outline and detailed planning application for the overall development. The risk of all sources of existing flooding are outlined, including the risk of tidal flooding to the site following a breach. The mitigation measures to deal with the flood risk on site are investigated and the potential hydraulic impacts that these will have on the surrounding area presented A site parameters master plan is included within Appendix A.

7 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 4 Capabilities on project: Water 3 Planning Policy 3.1 Lincolnshire Local Flood Risk Management Strategy The Lincolnshire Local Flood Risk Management Strategy (LFRMS) aims to increase the safety of people across Lincolnshire by reducing the number of people at risk of flooding, increasing the resilience of local communities and reducing the impact of flooding. The Joint Lincolnshire Flood Risk and Drainage Management Strategy developed through public and stakeholder consultation in 2011 and 2012 provides a partnership approach to co-ordinated management by all organisations with responsibilities for flood risk and drainage management across the county. 3.2 Lincolnshire Preliminary Flood Risk Assessment In accordance with the Flood Risk Regulations 2009, Lincolnshire County Council has produced a preliminary flood risk assessment. This was submitted to the Environment Agency in June The preliminary flood risk assessment applies only to flooding from surface water, groundwater, ordinary watercourses and canals. It does not include fluvial flood risk. The proposed development site is not within an Indicative flood risk area. 3.3 River Witham Catchment Flood Management Plan (CFMP) The EA Catchment Flood Management Plan (CFMP) documents present catchment based policies for the future management of flood risk throughout the catchment for the next 100 years. The River Witham CFMP covers the area in which the proposed development site is located The CFMP states that the catchment area is predominantly rural with the main urban areas being Lincoln and Boston. The majority of urban drainage within the CFMP is managed by Anglian Water with five Internal Drainage Boards (IDBs) maintaining non rivers and the EA responsible for sea defences and works on main rivers Current flood risk in the area is associated with the River Witham, its tributaries and the sea. It is reported that tidal flooding from the Haven and overtopping of the tidal defences could inundate large parts of Boston The CFMP reports that climate change will cause the largest increase in flood risk in the future in this area through a combination of higher peak flows and more extreme flood levels. Policy Unit 10 covers Boston Town and includes the tidal Haven. The report state that there is a substantial risk from tidal flooding within this policy unit and indicates that climate change will significantly increase the risk. The CFMP recommends the adoption of Policy 5 ( Take further action to reduce flood risk now and/or in the future ) to allow the tidal flood risk in Boston to be reduced, including the impact of climate change. 3.4 Boston Borough Level 1 Strategic Flood Risk Assessment The Boston Borough Council SFRA published in October 2009 was produced to support the development of Boston. The SFRA identified that Boston, and the proposed development site, falls predominantly within the River Witham river catchment. The SFRA identifies tidal risk sources to the proposed development site from the Wash Banks and the Boston Haven (and Witham Outfall Channel) and fluvial flood risk sources to the site from the River Witham (upstream of Grand Sluice) and South Forty Foot Drain. Within the original SFRA report, published 2002, these four sources of flooding were considered the primary flood risk to the Boston area When overtopping of a large embanked watercourse such as the River Witham occurs the depth of water flowing over the flood bank or wall is likely to be small, a few centimetres at most. The bank will act like a weir and the rate of flow per unit length of bank will be relatively modest and this, provided that the duration of overtopping is finite, will limit the volume of water cascading over defences to cause flooding within the defended area. The SFRA indicates that the situation will become far more critical if overtopping of an embankment erodes the crest leading to a breach in the embankment. In this situation as the crest of the bank is washed away the flow though the initial gap increases and a small breach is created. This becomes steadily bigger as increasing flows pass through it and a rapid and progressive failure of the embankment follows. In an extreme event this may only take minutes The breaching of tidal flood embankments has two additional factors to those described above which compound the risk of failure. Severe wave action, such as in a storm surge can increase wave action and increase water levels by up to a

8 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 5 Capabilities on project: Water metre or more higher than normal spring tides. This can cause storm waves to break on the flood bank itself and thus the energy released can cause serious physical damage to the embankment. This impact is of greater relevance to defences exposed to the open sea, such as those along the shores of the Wash, than those along tidal estuaries, such as the Boston Haven. Secondly, in a storm surge the peak tide level (as well as the wave heights) will be considerably greater than normal and large volumes of tidal water may wash over the top of the flood bank on the crest of every wave. Although this wave crest overtopping will only occur for a relatively short time at the peak of the tide, while it does occur the flood bank will be subject to severe risk of erosion, and consequent failure, even though the peak tide level itself may still be well below the top of the embankment BSIDB are identified as the IDB which have responsibility for the area in which the proposed development site lies. The IDB maintains its drains for a standard of flood protection between a 10% (1 in 10 year) and a 1.3% (1 in 75%). Hydraulic modelling carried out for Wyberton Towns Drain indicates a flood level of 1.61m AOD on London Road (B1397) and 1.63m AOD along the Wyberton Bypass (A16). 3.5 Sequential Test NPPF aims to ensure inappropriate development is avoided in areas at risk of flooding. The Sequential Test, required under NPPF, is a tool for determining land uses that are compatible with the level of flood risk at each development site within a Local Authority area The Environment Agency produces Flood Zones that are the starting point for the Sequential Test. Flood Zones 2 and 3 indicate land at medium high probability of flooding during extreme events, and Flood Zone 1 is the low probability zone (all land outside Zones 2 and 3). These flood zones refer to the probability of sea and river flooding only, excluding any existing defences Table 2 summarises the annual probability of flooding in relation to the Flood Zones and the land uses considered appropriate for each Zone. It is based upon Tables 1, 2 and 3 of the NPPF Planning Practice Guidance. Table2: Flood Zones and Appropriate Land Use Flood Zone Annual Probability of Flooding Appropriate Land Uses Flood Zone 1 Flood Zone 2 Flood Zone 3a Flood Zone 3b < 1 in 1000 (0.1%) annual probability of flooding in any given year. 1 in in 1000 (1% - 0.1%) annual probability of river flooding in any given year; or 1 in in 1000 (1% - 0.1%) annual probability of tidal flooding in any given year. >1 in 100 (1%) annual probability of river flooding in any given year; or >1 in 200 (1%) annual probability of tidal flooding in any given year. Functional Flood Plain comprises land where water has to flow or be stored in times of flood. All land uses Essential Infrastructure Highly Vulnerable subject to Exception Test More vulnerable Less vulnerable Water compatible Essential infrastructure subject to Exception Test Less vulnerable More Vulnerable subject to Exception Test Water compatible Essential infrastructure subject to Exception Test Water compatible The proposed food store, commercial buildings and BUFC stadium can be classed as Less Vulnerable under the general heading Buildings used for shops; financial, professional and other services; restaurants, cafe and hot food

9 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 6 Capabilities on project: Water takeaways; offices; general industry, storage and distribution...and assembly and leisure. Less Vulnerable development is considered appropriately located within Flood Zone 3a (1% AEP) In relation to NPPF the residential areas and proposed hotel can be classed as More Vulnerable under the general heading Buildings used for dwelling houses... and hotels. For More Vulnerable development to be appropriately situated within the 1% AEP flood extent the Exception Test must be passed The proposed petrol station has been classed as Highly Vulnerable under the general heading Installations requiring hazardous substances consent. Whilst under NPPF Highly Vulnerable development is not sequentially appropriate in Flood Zone 3a, it is noted that much of Boston lies within this flood zone. As such, it is argued that this development will be suitable following the implementation of mitigation measures, specifically ground raising, as detailed in Section 6.1. It is suggested that the proposed petrol station is located on the development platform As outlined above, the Environment Agency flood maps show that the whole site lies within Flood Zone 3 and is defined as having a high probability of flooding. As such, the relative probability of flooding and residual risk of flooding (future flood hazard for the year 2115) presented within the SFRA, and further information provided by the EA, has been studied to better inform the Sequential Test In carrying out the Sequential Test guidance was sought from Boston Borough Council to determine: The datasets to be used primarily as the majority of Boston is within Flood Zone 3; Confirmation of the area within which the Sequential Test should be carried out for the different elements of the development, i.e. residential, commercial, BUFC stadium; Known potential development sites that should be considered; and Any specific search criteria required by Boston Borough Council for the different planning elements mentioned above The search area that has been used has been defined by Boston Borough Council follows the local authority boundary. The only exception is the proposed BUFC stadium for which it was suggested that the search area should be at least district wide. Each proposed land use has been looked at separately with residential, retail, commercial and assembly and leisure considered in turn; 1. Residential Information obtained from Boston Borough Council indicates that there are no local plan allocations remaining that have not been built or commenced which can be pointed to in order to show the availability of housing land; As a result, local plan allocations cannot assist in identifying sequentially preferable sites. Whilst some significant sites have received development consents over the past 18 months it is indicated that these do not meet the housing supply deficit. As a result it is suggested that no other sequentially preferable sites are available. However, given that residential housing is classed as a highly vulnerable, the Exception Test will be required for this component of the development and it is recommended that the Sequential Approach to development be considered. 2. Retail The only other site identified for retail development within the search area is the Wide Bargate/Red Lion Street Site which is shown to be at higher risk but lower probability of flooding than the proposed development site. However, the site has been refused planning permission on access grounds and it is suggested that this site is unsuitable for

10 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 7 Capabilities on project: Water retail development. Based on the size (7,000 sq m) and proposed use (food superstore) of retail development at the Tytton Lane site, Boston Borough Council is unable to point to a retail site that is sequentially more preferable or reasonably more available. 3. Commercial The proposed commercial uses suggested at the site are listed as a restaurant, pub, drive through and hotel. It is indicated that there are two sites on which outline planning approval has been granted for hotel developments. Swineshead Road has mixed hazard danger for all and danger for most and the undeveloped parts of a larger outline at Enterprise Park at Boardsides (not included in the outline approval), appear to be in the same hazard category as the Tytton Lane site. Based on the above review Boston Borough Council indicates that there are no other live consents with hotels or sites that are reasonably available, and, on this basis, it is considered that the Tytton Lane site is sequentially preferable for commercial development. Other than the hotel all of these uses are considered less vulnerable and so are acceptable in Flood Zone 3a. The hotel is classed as residential use vulnerability (highly vulnerable) and as such requires the Exception Test. 4. Assembly and Leisure (BUFC Stadium) Given the scale of this part of the proposed development there are no allocations or sites for uses on this scale that can be referred to. It is suggested that the search area used depends on local circumstances and the likely catchment for the category of development that is being proposed and therefore it is suggested that the search area is at least district wide. Further consideration needs to be given to the local circumstances and the likely catchment for the category of development that is being proposed. It is also indicated that the application of the Exception Test, whilst not directly relevant to this category of development, may be beneficial in demonstrating wider sustainability benefits to locating the development at this site The guidance from Boston Borough Council presented above indicates that there are no other sites sequentially preferable for residential, commercial or retail use than the proposed development site at Tytton Lane. As such, the above suggests that development in this location meets the requirements of the Sequential Test. 3.6 Exception Test NPPF indicates that if, following the application of the Sequential Test, it is not possible for development to be located in area with a lower probability of flooding, the Exception Test must be applied where appropriate. For the Exception test to be passed: it must be demonstrated that the development provides wider sustainability benefits to the community that outweigh flood risk, informed by a Strategic Flood Risk Assessment where one has been prepared; and a site-specific flood risk assessment must demonstrate that the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible will reduce flood risk overall. Both elements must be passed in order for development to be allocated or permitted An Exception Test is required for the proposed development as some if the proposed uses of the site are considered Highly Vulnerable. These include the residential dwelling and proposed hotel. 1. Residential As discussed as part of the Sequential test Boston Borough Council has indicated that there are no other available sites within Boston in which to locate residential development. It is also confirmed that the recent developments that have

11 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 8 Capabilities on project: Water taken place, or are in the process of being completed, are not sufficient to meet the current supply deficit. As such it is suggested that the development for residential purposes will address this deficit and thus deliver wider sustainability benefits for the community that outweigh the potential flood risk. In order to ensure that residential developments remain at low risk of flooding for their lifetime, the following mitigation measures are suggested: The Sequential Approach to development should be considered to ensure that the most vulnerable uses of the development site are located in the areas of least risk if practicable; Given expected flood depths over the lifetime of the development, the site is not currently suitable for single storey development. Dwellings must be a minimum two storey with no ground floor habitable accommodation. In addition the first floor accommodation must be above the highest predicted flood level; The construction of 500 three storey houses as dictated above is not compatible with the developer vision for the site. As such it is suggested that raising ground levels over certain areas of the site could mitigate for this. Ground raising would enable the construction of a mix of traditional one, two and three storey buildings where the ground levels are above the height of the flood levels thus creating a more varied development; Consultation with the Environment Agency has indicated that a proposal for ground raising would not be objected to in principle, however any proposal would need to be accompanied by detailed information to demonstrate that flood risk to the surrounding area will not be significantly increased as a result of these works. As a minimum it is suggested that: o hydraulic modelling would need to be carried out to understand the change in hazard, depths and velocities around any development platform in the floodplain over the lifetime if the development; o single storey development should consider the 0.1% future scenario for establishing a suitable finished floor level; and o development proposals that do not include ground floor sleeping can consider the 0.5% scenario, over the lifetime of the development. A further freeboard of mm is likely to be required above the flood level to allow for any modelling inaccuracies, and ensure the risk to development remains low. 2. Hotel The Sequential Test outlined that there are no other areas within the boundaries of the search that are sequentially preferable for locating a hotel. Development of this nature will provide wider sustainability benefits for the local community by providing a source of employment, potentially increasing income for surrounding businesses in the form of tourism revenue and increasing the provision of additional accommodation in the area. These benefits are considered to outweigh the risk from flooding. In order that the hotel remains at low risk of flooding for its lifetime, the following mitigation measures are suggested: Uses more compatible with high levels of risk, for example garages or utility spaces, should be located at ground floor level; and Sleeping accommodation should be located on at least the first storey and must be above the highest predicted flood depth.

12 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 9 Capabilities on project: Water 3. Other Site Uses Whilst the Exception Test is not required for less vulnerable aspects of the development the following mitigation measures are recommended: An area of safe refuge should be provided above the expected flood depth over the lifetime of the development At this juncture it should be noted that the above requirement could be used in support of locating the BUFC stadium at the Tytton Lane site. A stadium of the size proposed, if constructed at a level which is at low risk of flooding, could provide the location for this required refuge area as well as providing wider sustainability benefits in the form of employment and increased revenue to the area. Advice should be taken from the Emergency Services in order that consideration is given to safe access and egress routes. Consideration should also be given to developing a robust evacuation plan for the whole site. 3.7 Sequential Approach The Sequential Approach is a risk based approach to development which directs the most vulnerable types of development towards the areas of lowest risk. The EA maps presented in Appendix B have been used to carry out the following assessment. As discussed above, the maps demonstrate that the risk of flooding from a breach or overtopping even is relatively uniform across the site and on this basis it could be concluded that there is no area of lower risk which would be preferable for siting the most vulnerable development. Due to the uniformity of risk across the site mitigation, in the form of ground raising, has been proposed. As a result of ground raising all vulnerable development will be effectively situated outside of Flood Zone 3a once complete. The development platform and further mitigation measures proposed for the site are discussed further in Chapter 6.

13 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 10 Capabilities on project: Water 4 Flood Risk 4.1 Tidal Flooding The current Environment Agency online Flood Maps (Figure 2) show the majority of Boston Town to be located within Flood Zone 3 and as such the whole area is classed as having a high probability of fluvial or tidal flooding. The proposed development site is within this area and so has a >1% Annual Exceedence Probability (AEP) (1 in 100 year) of fluvial flooding and a 0.5% AEP (1 in 200 year) or greater chance of tidal flooding The Environment Agency publishes Flood Risk Zone Maps which relate to the likelihood and magnitude of fluvial and tidal flooding in a given area. The existing Flood Zones held by the Environment Agency for the Boston area (shown in Figure 2) indicates fluvial or tidal flood risk across the site, showing that the proposed development is located within: Flood Zone 3 (high probability) as represented by the darker blue shading - land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%), or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year. Figure 2. Environment Agency Flood Map for Planning with proposed development site highlighted (accessed: ) As flood risk is uniform across the site more detailed maps extracted from the SFRA have been used to differentiate areas within the Boston Town area, taking present flood defences into consideration Relative Probability of Flooding Within the SFRA, hydraulic modelling of the 1% (1 in 100 year) and 0.1% (1 in 1000 year) fluvial flood event and 0.5% (1 in 200 year) and 0.1% (1 in 1000 year) tidal flood event was carried out to determine the relative probability of flooding at the proposed development site taking present flood defences into account. Flooding was assumed to occur when a flood embankment overtopped. Where the defence was an earth embankment it was assumed that breaching would follow. Figure 3 indicates that the site is classified as having a medium relative probability of tidal flooding taking present flood defences into account.

14 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 11 Capabilities on project: Water Key Tidal Flood Probability Low Medium High Fluvial Flood Probability Low Medium Figure 3. Relative Flood Risk Map taken from Boston Borough Council SFRA (2010) Residual Risk of Flooding Residual risks of flooding arise from either extreme events with exceptionally high return periods (200+ years) or events which, due to their unpredictable nature, are not readily amenable to quantitative analysis, for example premature structural failure, serious operational or equipment failures or freak accidents which cannot be foreseen. The principal residual flood risk in the Boston area would be a result of premature failure of the flood embankments well before the defences were overtopped. The CFMP identifies that tidal flooding from the Haven and overtopping of the tidal defences could inundate large parts of Boston. Within the Boston Borough Council SFRA, a 2D model was developed for the 2115 climate change scenario to estimate the impact of a breach. The resulting future Flood Hazard Mapping (Figure 4) shows the entirety of the proposed development site is classed as being at high risk of residual flooding with danger for all should a breach of the present flood defences occur. It is noted that in the report this represents a worst case scenario and cannot be attributed to a particular magnitude event.

15 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 12 Capabilities on project: Water Key Flood Hazard 2115 Low Hazard Danger for Some Danger for Most Danger for All Figure 4. Flood Hazard Map (for 200 year event plus climate change) taken from Boston Borough Council SFRA (2010) Northern Area Tidal Breach Hazard Mapping Detailed maps from the Environment Agency Northern Area Tidal Hazard Mapping study have been obtained and reviewed to further ascertain the residual risk of flooding to the proposed development site in the event of a breach of the current defences. These are presented in Appendix B. For the 2115 (climate change) breach scenario the following is indicated: Hazard - During both the 0.5%AEP (1 in 200 year) event and 0.1%AEP (1 in 1000 year) event it is shown that the hazard rating is Danger for All across the whole site. Depth - For the 0.5%AEP scenario the depth following a breach is shown to be between 1 and 2 metres across the entirety of the site. For the 0.1%AEP event, the depth is shown to be between 1 and 2 metres across the majority of the site with some localised areas where the water depth is suggested to be greater than 2 metres. Velocity - The predicted velocity of water across the site is shown to be metres per second across the entire site for both the 0.5%AEP and 0.1%AEP scenarios Northern Area Tidal Overtopping Hazard Mapping Detailed maps from the Environment Agency Northern Area Tidal Hazard Mapping study have been obtained and reviewed to further ascertain the risk of flooding to the proposed development site in the event that the current defences are overtopped. These are presented in Appendix B. For the 2115 (climate change) overtopping scenario the following is indicated: Hazard - During the 0.5%AEP (1 in 200 year) event the hazard rating across the majority of the site is Danger for Most. There are some small areas where it is indicated that this risk is less and the hazard rating Danger for Some or Low Hazard. The same is true of the 0.1%AEP scenario, but the pockets of lower risk are smaller. Depth - In the 0.5%AEP scenario the depth following a breach is shown to be between metres across the majority of the site, with some small areas where the predicted depths are less (between m and m) and small areas where the predicted depths are greater (between 1-2m). During the 0.1%AEP event the depth of flooding is shown to be between metres across the majority of the site, with some localised areas where the predicted depth is greater (between 1-2metres) and small areas where the depth is less ( m). Velocity - The predicted velocity of flood water across the site is shown to be metres per second across the entire site for both the 0.5%AEP and 0.1%AEP scenarios.

16 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 13 Capabilities on project: Water 4.2 AECOM Tidal Breach Modelling The current Environment Agency modelling output, discussed above, which is provided in response to development enquiries presents a composite breach of all defences and as such represents a worst case scenario. More in depth hydraulic modelling was required to assess the risk of flooding to the proposed development site and to determine depths of water on site in the event of a breach in more detail Therefore, following the initial studies carried out as detailed above, AECOM were commissioned by Chestnut Homes Ltd to carry out flood modelling works to verify the existing base case flood risk conditions to the proposed Tytton Lane development site and to assess any change in flood risk to the site and surrounding area as a result of the design proposals This first phase of hydraulic modelling works has assessed the base case flooding scenario for the site in the event of a breach for both the 200 year and 1000 year return period. Both return periods have been modelled for present day (2006) and future climate change (2115) tidal levels in line with the current Environment Agency model of the East Coast of England which includes the Humber, East Coast and The Wash The package of modelling outputs can be found in Appendix C. Only the results for the 200 year event under a climate change scenario (2115) have been presented as this scenario is the design event the site will be protected to Hydraulic Modelling Two-dimensional hydraulic modelling has been carried out using the TUFLOW package. The model was obtained from the Environment Agency in February Breach location W29 has been used in the modelling undertaken, which is situated in The Wash (W) reach of the Northern Area Tidal Modelling study area, at the mouth of the Witham Haven The breach model considers the consequences of a tidal breach only as tidal risk is the dominant flood source in the area. Fluvial flooding and flooding from surface water or as a result of insufficient drainage capacity in is not considered as this is beyond the scope of works commissioned. In addition the breach model does not consider the probability of a breach occurring as that is beyond its scope, it only considers the consequences of a breach For each scenario the maximum flood depth and flood hazard (based on Flood Risk to People: FD2320) have been produced Development Platform As discussed with Chestnut Homes at the scoping stage of this hydraulic modelling work, three development scenarios have been considered for the proposed development platform Development Platform Scenario: This first scenario used a development platform covering 90% of the site. The entireties of the residential and commercial areas were raised to a height of 5m AOD, as was the BUFC stadium. The areas of car park were left at current ground level accounting for the remaining 10%. 5m AOD was used as a very worst case scenario based on analysis of the maximum flood depths on site under a 200 year plus climate change (2115) scenario (see Drawing No.3a for spot levels denoting maximum depths at certain points across the site). This scenario will allow the construction of standard houses across the development site, with no requirement for the ground floor level to be reserved for less vulnerable uses Development Platform Scenario: 002 The second scenario run created a platform covering 50% of the stadium area and 50% of the residential parcel. The stadium itself was raised, again to 5m AOD based on a worst case scenario, and the car parks left at current ground level. The north western corner of the site, allocated for residential development, was raised to 5m AOD. This location was chosen as it was felt that ground raising in this area would have the least detrimental impact to flood risk in the surrounding area. This scenario will allow the construction of standard houses on the development platform, with no requirement for the ground floor level to be reserved for less vulnerable uses. Residential properties which are not located on the development platform shall have the ground floor reserved for less vulnerable uses such as garages.

17 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 14 Capabilities on project: Water Development Platform Scenario: 003 A further third scenario was run for the 200yr 2115 event only, in which parts of the residential parcel designated for dwellings were raised to 5m AOD whilst the access roads through these areas remained at current ground level. This scenario will allow the construction of standard houses across the development site, with no requirement for the ground floor level to be reserved for less vulnerable uses, whilst reducing the overall land take of the platform in comparison to Development Platform Scenario It should be noted that whilst the development platform under all scenarios (001, 002 and 003) was raised to 5m in the model as a worst case scenario, the exact height required for the platform will be determined from the spot heights plan (Drawing No.3a). However for the purpose of modelling, the change in flood risk would be expected to be the same as long as the modelled platform is above the 200yr 2115 flood depths Hydraulic Modelling Results The results of the modelling carried out to date are presented in Appendix C. The following plans are included; o Drawing No. 1 Draft 200 Year Depth (2006) o Drawing No. 2 Draft 200 Year Hazard (2006) o Drawing No. 3 Draft 200 Year Depth Plus Climate Change (2115) o Drawing No. 3a Draft 200 Year Depth Plus Climate Change (2115) Spot Heights o Drawing No. 4 Draft 200 Year Hazard Plus Climate Change (2115) o Drawing No. 9 Draft 200 Year Depth Plus Climate Change (2115) Development Platform Scenario:001 o Drawing No. 10 Draft 200 Year Hazard Plus Climate Change (2115) Development Platform Scenario:001 o Drawing No. 13 Draft 200 Year Depth Plus Climate Change (2115) Development Platform Scenario:002 o Drawing No. 14 Draft 200 Year Hazard Plus Climate Change (2115) Development Platform Scenario:002 o Drawing No. 25 Draft 200 Year Depth Plus Climate Change (2115) Development Platform Scenario: 003 o Drawing No. 26 Draft 200 Year Hazard Plus Climate Change (2115) Development Platform Scenario: 003

18 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 15 Capabilities on project: Water Under Development Platform scenario 001 there is shown to be a slight increase in depths along the southern boundary, particularly along Causeway and in the area between Clarke Court and Cavendish Drive. The flood depth increase in this area is on average 0.07m. An increase in depths of approximately 0.1m is also shown along the eastern extent between the eastern site boundary and the Elmfield Cottage/Tytton Hall area. However the predominant land use in this area is agricultural. Under scenario 001 a decrease in flood depths is shown along the northern boundary of the site with depths of water decreasing along Tytton Lane East and the areas north of here by approximately 0.1m. Flood risk to existing residential areas is reduced along the western boundary of the development by, on average, 0.12m. Parts of Vine Crescent, Delfield Road, Deldale Road, Collingwood Close and Tytton Lane West are shown to benefit from the development platform A slight increase in the overall hazard rating is shown to the east of the site under scenario 001 and areas north of the northern boundary, in particular Yarborough Road are shown to experience an increase in hazard from Danger for Most to Danger for all. Along the southern boundary of the site parts of Clarke Court and Granville Avenue experience a similar increase in hazard. Significant parts of the existing residential area along the western boundary experience a decrease in hazard, from Danger for All to Danger for Most following the installation of the development platform Under Development Platform Scenario 002 similar results are indicated in terms of impact on the surrounding area. Slight increases in depths are shown along the southern boundary with depth increases shown along Causeway and the Cavendish Drive area. Increases along the eastern boundary are also shown, but once again land use in this area is predominantly agricultural. Similar decreases to the 001 scenario are shown along the northern extent with Tytton Lane East benefitting from reduced depths. The existing residential areas along the western boundary benefit from the development platform under the 002 scenario although it is noted that benefit to these areas is slightly less than under the 001 scenario. Under Scenario 002 depths on site are slightly increased through the central area A slight increase in hazard rating is shown along the southern and eastern boundaries of the site under 002 however, this is mainly in areas of agricultural land. Some increase in hazard is also indicated to the north of the site in particular in the area around Yarborough Road. In the existing residential area to the west of the site boundary Tytton Close, Collingwood Close and parts of Deldale Road and London Road benefit from a reduction in hazard following the installation of the development platform. There is some reduction in hazard on the site, in particular to areas surrounding the development platforms under Under Development Platform Scenario 003 there is shown to be a slight increase in depths along the southern boundary when compared to 1 in 200 year 2115 base case. In particular along Causeway and in the Clarke Court/Cavendish Drive area where depths increase by approximately 0.06m. To the east of the site there is some increase in depth between the east of the site and Wyberton Low Road, particularly in the area to the south of Tytton Hall where depths increase by around 0.06m. A marginal increase in depths, approximately 0.05m, is seen to the north east of the site. It is noted that the predominant land use in the areas to the east of the site is agricultural. The development platform scenario 003 reduces flood depth to the west of the site with a decrease in depth of approximately 0.1m shown along London Road, Vine Crescent, Delfield Road and Deldale Road. Tytton Road West and Collingwood Close are also shown to benefit from a reduction in flood depths of approximately 0.09m. A slight increase in flood depth on site (approximately 0.103m) is shown for one small area, immediately west of the A16, where parking areas are proposed. North of the site, along Tytton Lane East, depths are shown to decrease by around 0.11m, and in the associated residential area a decrease in flood depths of approximately 0.08m is seen Under 003 there is a slight increase in the overall hazard rating shown in areas to the east of Tytton Hall, which is predominantly agricultural land. Hazard is shown to increase from Danger for Most to Danger for All for some areas along Causeway and Clarke Court. Small areas along Granville Avenue and Solhem/Parthian Avenue are also shown to experience an increase in hazard under the 003 scenario. To the north of the site there is some increase in hazard shown along Tytton Lane East and the land to the north, in particular the land around Yarborough Road. A reduction in

19 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 16 Capabilities on project: Water hazard from Danger for All to Danger for Most is shown for a large proportion of the residential area immediately to the west of the site. A reduction in hazard is also seen to the north of Tytton Lane West and along London Road. There is some reduction in hazard on the site, in particular to areas surrounding the development platforms Other development sites in Boston have mitigated flood risk through one metre of ground raising with flood resilient construction used to make up the freeboard. This option can be taken forward subject to further discussions with the EA and Boston Borough Council on the scenarios tested to date Hydraulic Modelling Conclusions Following a review of the draft outputs it is shown that a development platform on the proposed site does not significantly change flood risk in the immediate area. Whilst there are some areas within the local vicinity, mainly to the south and east of the site, where a small increase in flood depths and hazards are experienced under all of the modelled scenarios, these are shown to be minimal in the order of 0.06m-0.1m. Some existing residential areas, particularly to the west and north of the proposed development, experience a positive effect in flood depths and hazard as a result of the platform with flood depths reduced by between 0.08m and 0.12m. It is recommended that the results of the modelling are discussed with the EA and local planning authority before proceeding with design development, to ensure that the level raising is considered acceptable to all parties. 4.3 Fluvial Flooding As shown in Figure 2 the entirety of the site falls within EA Flood Zone 3a and is shown to be at high risk of flooding from fluvial sources. However, as the predominant risk source to the proposed development site its tidal, fluvial flooding has not been considered further within this FRA. As tidal flooding is considered to be the main source of flooding, the mitigation proposed for tidal flooding is considered sufficient to mitigate for fluvial flooding. 4.4 Pluvial (Surface Water) Flooding Flooding from land may occur with intense, often short duration rainfall which is unable to soak into the ground or enter drainage systems. It is made worse when soils are saturated so that they cannot accept any more water. The excess water then ponds in low points, overflows or concentrates in minor drainage lines that are usually dry. Often there is limited warning before this type of localised flooding occurs, although the duration is usually short lived In the absence of a Surface Water Management Plan (SWMP) an initial review of the PFRA was carried out to determine the likelihood of pluvial flooding to the proposed development site. The Environment Agency Flood Map for Surface Water (FMfSW) presented within the PFRA, and information within the SFRA, indicates that the site is at low risk of surface water flooding The Environment Agency publishes Risk of Flooding from Surface Water (RFfSW) Maps which relate to the likelihood (high, medium, low and very low) of flooding from surface water in a given area. The depths and velocities (speed and direction) expected for each likelihood event are also given The Environment Agency RFfSW mapping for the Tytton Lane area (shown in Figure 5) indicates areas of surface water flood risk, confirming that the likelihood of surface water flooding occurring across the site are: Very low area assessed as having a less than 1 in 1,000 (0.1% AEP) change of flooding annually from surface water; and Low area assessed as having between a 1 in 100 (1% AEP) and 1 in 1,000 (0.1% AEP) chance of flooding from surface water in any given year. The RFfSW maps show that the majority of the site is at very low risk of pluvial flooding with some localised areas of low risk, predominantly associated with the field drains that bisect the site.

20 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 17 Capabilities on project: Water The Drainage Strategy summarised in Chapter 5 and presented in full in Appendix D, outlines that management strategies will be in place to ensure that the risk of pluvial flooding following development of the site, will remain low. Figure 5. Environment Agency Risk of Flooding from Surface Water (accessed ) 4.5 Groundwater Flooding The SFRA states that flooding from groundwater is of no relevance in the Boston area and this is confirmed by the EA Susceptibility of Groundwater Flooding Map presented in the Lincolnshire PFRA. During correspondence with the EA they stated that they are not aware of any history of groundwater flooding at the site or within the immediate vicinity (1km radius). The site is underlain by unproductive strata and as such the groundwater below the site is not considered to be a sensitive receptor. As such the proposed development site is not considered to be at risk of flooding from groundwater emergence. 4.6 Flooding from Artificial Waterbodies The current Environment Agency online Flood Maps and the PRFA indicate that flooding from reservoirs and other artificial water bodies such as canals are not significant in the Boston area. A qualitative assessment of four ponds located approximately 250m north east of the site suggests that they do not pose a risk of flooding to the proposed development site due to their relatively small volume, the flat topography of the site and given that they are regulated waterbodies. As such the risk to the proposed development site of flooding from artificial waterbodies is considered to be low. 4.7 Internal Drainage Board Drains Consultation with BSIDB indicates that all drains through the proposed development site, open and piped, are maintained on a rolling schedule that includes the removal of vegetation in the summer/autumn and de-silting of selected watercourses in the winter. Where drains are privately owned BSIDB provides advice and support in this regard. Modelling of these watercourses is not available however no recent or historical instances of flooding have been recorded from any of the drains at the proposed site. As such the IDB drains are not considered to pose a significant risk of flooding to the site.

21 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 18 Capabilities on project: Water The Master Planning stage should take into account the locations of these drains and must take account of the relevant byelaws and requirements for consent. A commitment to future maintenance should be included in any management proposals for the development, to ensure that the drains remain in a good condition and do not pose a future flood risk.

22 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 19 Capabilities on project: Water 5 Surface Water Management 5.1 Public Sewer Network The public sewer network in this area is managed by Anglian Water. In their pre-development assessment report (October 2011) Anglian Water confirmed that there are no surface water sewers in the vicinity of the site. Given the land use of the existing site it is not envisaged that there are any existing foul water sewers crossing the site. An existing foul water sewer has been indentified running along the western boundary of the site. As Anglian Water have a statutory duty to maintain its assets the probability of sewer flooding affecting the proposed development is deemed unlikely. 5.2 Drainage Statement A standalone Drainage Statement has been prepared by Hall Infrastructure Design Ltd, that contains a concept drainage design to inform the master planning process for the proposed development. The full statement is provided in Appendix D and summarised below The information in this section has been summarised from the Drainage Statement, with supplementary guidance and assessment by AECOM. 5.3 Existing Surface Water Management Topographic surveys of the proposed development site show that the land is generally flat with an average level 2.2m - 2.3m above ordnance datum (AOD). At its lowest point the site level is approximately 1.9m AOD, rising to approximately 3.1m AOD at its highest point As stated in Chapter 2 the site is approximately 29 Ha in area and is drained by a number of local open riparian drains with assumed tile land drainage, piped culverts and BSIDB maintained watercourses including the Towns Drain. For the purposes of drainage design the proposed site area has been sub divided as detailed in Table Existing green field run off values and volumes have been calculated using the ICP SuDS Mean Annual Flood Method and the Microdrainage green field runoff calculations are shown in Table 3. Table 3. Green field run off values and volumes for the existing site Site Sub Phase Area (Ha) 2 year (l/s) 30 year (l/s) 100 year (l/s) Residential (100 units) Residential (150 units) Residential (250 units) Foodstore Commercial Area Commercial Area Commercial Area BUFC Stadium Primary Road & Link Total

23 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 20 Capabilities on project: Water Preliminary soakaway tests in accordance with BRE Digest 365, were carried out on site in September These indicate that the site generally comprises 500mm of dark brown silty clay over a 700mm light brown silty layer underlain by light brown, slightly clayey silt. Ground water levels were noted to be in excess of 1.5m below ground level It has been recommended that for full depth traditional soakaways an infiltration rate of 5 x 10-7ms be adopted and for shallow soakaways an infiltration rate of 5 x 10-6ms be adopted. Soakaway testing has been carried out and shown that full depth traditional soakaways will not drain down within the permitted 24 hour half drain down period and the use of these soakaways has therefore been discounted. 5.4 Proposed Surface Water Drainage In accordance with NPPF a hierarchy of surface water discharge has been followed. This hierarchy is as follows: 1. Infiltration 2. Watercourse 3. Public Sewer Table 4 outlines the proposed changes in impermeable area as a result of the development and the proposed surface water drainage method of each site sub phase. Table 4. Changes in impermeable area as a result of development and proposed method of surface water drainage Site Sub Phase Existing Area (Ha) Area Impermeable post development (Ha) Area Impermeable post development (%) Method of surface water drainage for each site sub phase (% of impermeable area) Infiltration (%) Watercourse (%) Public Sewer (%)* Residential (100 ) Residential (150) Residential (250) Foodstore Commercial Area Commercial Area Commercial Area BUFC Stadium Primary Road & Link *Note: There are no proposals for and surface water from any of the sub phases to discharge to public sewers as Anglian Water have confirmed that there are no surface water sewers in the vicinity of the development The concept drainage design includes the use of infiltration SuDS and source control SuDS throughout all sub phases of the development. Permeable surfaces provide flood and pollution reduction whilst proposed soakaways and the North- South storage drain provide flood and pollution reduction as well as added landscape benefits. It may be possible to accommodate other features such as swales and infiltration trenches at the detailed design stage. Similarly it may be possible to accommodate riparian drains (given their post development use will otherwise be diminished) into attenuation for the proposed site In order to protect the receiving aquifer, watercourse or sewer from pollution, CIRIA Report C522 (Sustainable Urban Drainage Systems Design Manual for England and Wales, 2000) suggests an approach for setting the level of treatment that surface water runoff will pass through before being discharged. The CIRIA Report suggests that one level

24 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 21 Capabilities on project: Water of treatment is provided for residential developments, two levels of treatment are provided for non-residential developments and three levels of treatment are provided for industrial developments The Flood Water Management Act 2010 has identified a need for SuDS to be approved by local approving bodies known as SuDS Approval Bodies (SABs). The date of implementation of SABs is yet to be confirmed. The Act makes the use of SuDS compulsory where applicable on Site and requires new developments in England and Wales to have their drainage proposals approved by SABs on all projects where there is more than one curtilage. The SAB will be responsible for adopting and maintaining SuDS which are submitted for approval SuDS must be maintained correctly to ensure their safe operation and that flood risk on or off Site is not increased. The scope of implementation of such systems should be considered at detail design in conjunction with the relevant SAB Table 5 outlines the type of SuDS that could potentially be used within the development. It should be noted that not all SuDS methods are suitable or necessary for all developments. Many factors, such as available space and ground conditions, will influence the choice of methods for a particular development. Further ground investigations are necessary to determine the suitability of the Site for SuDS applications.

25 22 Table 5: Capability of different SuDS techniques (Extract from CIRIA C697, Table 1.7) Management Train Suitability Water Quantity Water Quality Environment al Benefits Technique Description Prevention Conveyance Pre-treatment Source control Site Control Regional Control Conveyance Detention Infiltration Water Harvesting Sedimentation Filtration Adsorption Biodegradation Volatilisation Precipitation Uptake by plants Nitrification Aesthetics Amenity Ecology Water butts, site layout Good housekeeping and design practices. and management Pervious pavement Allow infiltration of rainwater into underlying construction/soil. Filter drain Linear drains/ trenches filled with a permeable, often with a perforated pipe at the base of the trench. Filter strips Vegetated strips of gently sloping ground designed to drain water from impermeable areas and filter out silt and other particulates. Swales Shallow vegetated channels that conduct and/or retain water (and can permit infiltration when underlined). The vegetation filters particulates. Ponds Depressions used for storing and treating water. They have a permanent pool and bankside emergent and aquatic vegetation. Wetlands As ponds, but the runoff flows slowly but continuously through aquatic vegetation that attenuates and filters the flow. Shallower than ponds. Detention Basin Dry depressions designed to store water for a specified retention time. Soakaways Sub-surface structures that store and dispose of water via infiltration. Infiltration Trenches As filter drains, but allowing infiltration through trench base and sides. Infiltration basins Depressions that store and dispose of water via infiltration. Green roofs Vegetated roofs that reduce runoff volume and rate. Bioretention areas Vegetated areas for collecting and treating water before discharge downstream, or to the ground via infiltration. Sand filters Treatment devices using sand beds as filter media. Silt removal devices Manhole and/or proprietary devices to remove silt. Pipes, subsurface Conduits and their accessories as conveyance measures and/or storage storage. Water quality can be targeted using sedimentation and filter media. Key Recommended Some opportunities, subject to design

26 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 23 Capabilities on project: Water 5.5 Proposed Foul Water Drainage In regard to foul water drainage for the site, Anglian Water have confirmed that: 1. Limited (4 l/s) foul water discharge may be connected into their existing foul sewer network; 2. Remaining flows will need to discharge directly to Frampton Sewerage Treatment Works approximately 1.7km south of the proposed development site; and 3. There is scope to accept temporary low flow gravity connections into local infrastructure in advance of a strategic solution Connection into the existing sewerage network is considered too problematic due to location and invert level to use as a gravity outfall location. It is however suggested that, subject to agreement with Anglian Water, this option could be used as an initial temporary discharge point for pumped flows It is proposed that a pumping station and rising main will be established through requisition by Anglian Water Serviced Ltd. to serve the development. Anglian Water Services Ltd have been approached to undertake a costing and timescale analysis with regard to foul water discharge solutions for the development site.

27 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 24 Capabilities on project: Water 6 Flood Risk Mitigation 6.1 Development Platform Due to the proposed development site being located entirely within EA Flood Zone 3a, and containing a mixture of Highly Vulnerable, More Vulnerable and Less Vulnerable land uses, mitigation in the form of ground raising is proposed. This would ensure that all development was raised above the tidal breach flood level as defined in the AECOM tidal breach modelling as detailed in Chapter Three scenarios are proposed (001, 002 and 003 as detailed in 4.2) in which a development platform is constructed to the flood depth determined by the hydraulic modelling. Flood depths on site for a 200 year event plus allowance for climate change (2115) have been used. It is envisaged that ground raising on site will be between 1m and 2m above present ground levels on site. Spot heights for the 200 year plus climate change depth are presented in Appendix C, Drawing No. 3a Due to the outline nature of this application, three scenarios have been presented for this site. The preferred option for this site has yet to be determined, subject to further discussions with the EA and Boston Borough Council. Whilst it is noted that all three ground raising scenarios result in a minimal increase in flood depths to the surrounding area, the preferred scenario from a flood risk point of view is Scenario 002 in which 50% of the stadium parcel and 50% of the residential parcel are raised A further scenario, in which the ground is raised to 1m with the rest of the freeboard accounted for using flood resilient construction, has been identified and can be taken forward subject to further discussion on the scenarios modelled to date. 6.2 Flood Resilient/Resistant Construction As defined under NPPF residual risks are those remaining after applying the sequential approach and taking mitigations measures. As such flood resistance and resilience measures have been considered for use at the proposed development Flood Resilient measures are defined as buildings designed to reduce the consequences of flooding and facilitate recovery from the effects sooner than conventional buildings. Flood resistant construction can prevent entry of water or minimise the amount of water that may enter a building when there is flooding outside NPPF notes that the use of flood resilient construction is preferred as it can be achieved more consistently and is less likely to encourage occupiers to remain in buildings that can be inundated by rapidly rising water levels. Additional to the ground raising proposed above, it is suggested that flood resilience is incorporated into all development on the proposed site In order to reduce the amount of ground raising on site, freeboard above the modelled depth has not been considered. Therefore to account for modelling uncertainty, a suitable freeboard is incorporated through the use of flood resilient construction. Where buildings are to be constructed on the development platform proposed above, the following measures are recommended: Use of water resistant materials for floors, walls and fixtures; Siting of electrical controls, cables and appliances at least 300mm above the flood depth; and Consideration of lower floors for uses compatible with flooding.

28 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 25 Capabilities on project: Water Where development is not to be sited upon raised ground it is recommended that the above flood resilient construction measures are incorporated up to 600mm above the existing ground level, in addition to the reservation of the ground floor level for less vulnerable uses such as garages Subject to further discussion with the EA and Boston Borough Council, it has been suggested that the height of the development platform is increased by 300mm to account for the freeboard required, in place of using flood resilient construction methods. This would allow conventional building techniques to be used on these areas of the site. 6.3 Access and Egress It is noted that the development platform will be designed to be out of the floodplain and thus areas of raised ground across the proposed development site should be safe in the event in the event of a breach. The additional use of flood resilient design should mean that development located on the platform will be safe in a flooding event Where development is sited at existing ground level, or should there be a requirement to evacuate the raised areas of site, it is recommended that both pedestrians and vehicles exit the site eastward to London Road. This area is shown to be an area of lower hazard, with lower flood depths under both development platform scenarios. 6.4 Safe Haven It has been indicated that there is potential for the proposed BUFC Stadium to be used as a Safe Haven, subject to further consultation with Lincolnshire County Council and Lincolnshire Fire and Rescue Service.

29 AECOM Q1 (The Quadrant) Boston Flood Risk Assessment 26 Capabilities on project: Water 7 Conclusions The development site is located approximately 2km south west of the centre of Boston, Lincolnshire, at grid reference TF The proposed development site is currently agricultural land bordered to the north and south by existing residential dwellings and to the east by further agricultural land. An IDB drain, Wyberton Towns Drain, also runs along the southern boundary of the site The tidally influenced Boston Haven, which provides the outfall for the entire River Witham catchment, flows in a south-easterly direction approximately 2km to the east of the site, before discharging into the North Sea The Environment Agency flood zone maps show the site is located entirely within Flood Zone 3a and as such there was a requirement to produce more detailed site specific tidal breach modelling. Three scenarios (001, 002 and 003) were modelled for the 200 year event plus climate change (2115) The results of this modelling have shown that mitigation in the form of a development platform on the proposed site will not significantly change flood risk in the immediate area. Whilst there are some areas within the local vicinity, mainly to the south of the site, where a small increase in flood depths and hazards are experienced, these are predominately agricultural areas. Some existing residential areas, particularly to the west of the proposed development, experience a positive effect in flood depths and hazard as a result of the platform. Based on modelling outputs Scenario 002 is outlined as the preferred scenario from a flood risk point of view for the new development The site is at low risk of flooding from groundwater, pluvial and sewer flooding. The risk of flooding from artificial waterbodies within the vicinity of the site and IDB is also shown to be low. As tidal flooding is the predominant risk source to the development, fluvial flooding has not been considered further A number of options have been provided for surface water attenuation to Greenfield rates which will be considered further at detailed design stage Flood mitigation in the form of a development platform, raised to the 200 year plus climate change (2115) flood depth, is proposed. Based on tidal breach hydraulic modelling carried out by AECOM it is suggested that the development platform will be between 1m and 2m above existing ground levels. Further details on flood depths above ground level are presented in Appendix C, Drawing No. 3a The extent of the development platform is to be confirmed. Residential properties which are not located on the development platform shall have the ground floor reserved for less vulnerable uses such as garages The use of flood resilient construction methods, in conjunction with ground raising, is recommended for all buildings constructed on the proposed development site Access and egress routes have been identified which are situated in an area of lower hazard and lower flood depths. The use of the BUFC Stadium as a safe haven should be investigated further.

30 Appendix A Masterplan PARAMETERS PLAN

31

32 Appendix B Consultation ENVIRONMENT AGENCY CONSULTATION BOSTON BOROUGH COUNCIL CONSULTATION BLACK SLUICE INTERNAL DRAINAGE BOARD CONSULTATION

33 Matthew Stokes Aecom Our ref: CCN/2013/35308 Your ref: Date: 15 October 2013 Dear Matthew Request for information under the Freedom of Information Act 2000 (FOIA) / Environmental Information Regulations 2004 (EIR) Thank you for your of 1 October Requests for information that is recorded are generally governed by the Freedom of Information Act 2000 (FOIA).The information you have requested is environmental and it is therefore exempted from the provisions of FOIA by FOIA s.39(1). We have therefore considered your request under the provisions of the Environmental Information Regulations 2004 (EIR). Hazard Mapping Breaching Enclosed with this letter is a plan showing the location of the breaches we have modelled, together with four plans showing the maximum values of flood depth, velocity and hazard rating (danger to people) for the following scenarios: Year 2006 Year 2006 Year 2115 Year % (1 in 200) chance event 0.1% (1 in 1000) chance event 0.5% (1 in 200) chance event 0.1% (1 in 1000) chance event Hazard Mapping Overtopping Please find enclosed two plans showing the maximum values of flood depth, velocity and hazard rating (danger to people) resulting from simulated overtopping of defences. The plans show data for the following scenarios: Year 2115 Year % (1 in 200) chance event 0.1% (1 in 1000) chance event Your site is not affected by overtopping for the present day (2006) scenarios. It is important that you read the contextual notes on the maps. Waterside House, Waterside North, Lincoln, LN2 5HA. Customer services line: enquiries@environment-agency.gov.uk Calls to 03 numbers cost the same as calls to standard geographic numbers (i.e. numbers beginning with 01 or 02

34 Groundwater information We are not aware of any history of groundwater flooding at this location or within its immediate vicinity (i.e. within 1 km radius). The site is underlain by unproductive strata, superficial geology - clay + silt and bedrock mudstone. As such groundwater below the site is not considered to be a sensitive receptor. We do not have any records to show that contamination issues have been investigated on site and as such we are unable to comment on whether or not there are known issues. We would therefore recommend that you contact the Local Authority who are the principal regulators for the contaminated land regime. I hope the information is of use to you. Should you have any further queries please do not hesitate to contact me again. This information is subject to the attached notice, which we advise you read. If you are not satisfied with our response to your request for information you can contact us to ask for our decision to be reviewed. If you are still not satisfied following this, you can then make an appeal to the Information Commissioner, who is the statutory regulator for Freedom of Information. The address is: Office of the Information Commissioner, Wycliffe House, Water Lane, Wilmslow, Cheshire SK9 5AF. Tel: Fax: mail@ico.gsi.gov.uk. Website: http// Yours sincerely Katie Bonnett (Mrs) Customers and Engagement Officer Direct dial: Katie.bonnett@environment-agency.gov.uk Awarded to the Environment, Planning & Engagement Department, Anglian Region, Northern Area

35 Use of Environment Agency Information for Flood Risk / Flood Consequence Assessments Important If you have requested this information to help inform a development proposal, then we recommend that you undertake a formal pre-application enquiry using the form available from our website:- Depending on the enquiry, we may also provide advice on other issues related to our responsibilities including flooding, waste, land contamination, water quality, biodiversity, navigation, pollution, water resources, foul drainage or Environmental Impact Assessment. In England, you should refer to the Environment Agency s Flood Risk Standing Advice, the technical guidance to the National Planning Policy Framework and the existing PPS25 Practice Guide for information about what flood risk assessment is needed for new development in the different Flood Zones. These documents can be accessed via: idance ate You should also consult the Strategic Flood Risk Assessment produced by your local planning authority. In Wales, you should refer to TAN15 for information about what flood consequence assessment is needed for new development in the different flood zones zb3ylczf20xn7lk3zk0nmk! ?orig=/topics/planning/policy/tans/tan15/ You should also consult the Strategic Flood Consequence Assessment if one has been produced by your local planning authority.

36 In both England and Wales you should note that: 1. Information supplied by the Environment Agency may be used to assist in producing a Flood Risk / Consequence Assessment (FRA / FCA) where one is required, but does not constitute such an assessment on its own. 2. This information covers flood risk from main rivers and the sea, and you will need to consider other potential sources of flooding, such as groundwater or overland runoff. The information produced by the local planning authority referred to above may assist here. 3. Where a planning application requires a FRA / FCA and this is not submitted or deficient, the Environment Agency may well raise an objection. 4. For more significant proposals in higher flood risk areas, we would be pleased to discuss details with you ahead of making any planning application, and you should also discuss the matter with your local planning authority.

37 Modelled Breach Locations Kilometres This map indicates the location of where we have modelled the consequence of breaches in the defences along the coastline and tidal rivers. We have mapped the the maximum values of Hazard Rating (Danger to People), Depth and Velocity. We have not assumed that all breaches occur at the same time, but have modelled each breach individually and overlaid the results to find the maximum values. Our modelling only considers the consequences of a breach, it does not make any assumption about the likelihood of a breach occurring. Our defences generally provide a good standard of flood defence but a risk of breaching remains. Please contact the Environment Agency for information on how these maps are used in the management of flood risk. General Enquiries No: Weekday daytime calls cost 8p plus up to 6ppm from BT Weekend Unlimited. Mobile and other providers charges may vary Produced by th e Flood Risk Mapp ing & Data Manag emen t Team, Lin coln General Enqui ries No: Northern Area Tidal Hazard Mapping Location of Modelled Breaches This map is reproduced by permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office. Crown copyright. All rights reserved. Environment Agency , Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.

38 Max Hazard Max Depth Max Velocity Kilometres Kilometres Kilometres Modelled Breach Locations - see also the accompanying plan "Location of Modelled Breaches" Max Hazard Max Depth (m) Max Velocity (m/s) (Flood Risk to People : FD2320) Less than 0.75 (Low Hazard) Between 0.75 and 1.25 (Danger for Some) Date Printed Between 1.25 and 2.0 (Danger for Most) Greater than 2.0 (Danger for All) October 2013 Scenario year Scenario Annual Chance % (1 in 200) This map shows the level of flood hazard to people (called a hazard rating) if our flood defences are breached at certain locations, for a range of scenarios. The hazard rating depends on the depth and velocity of floodwater, and maximum values of these are also mapped. The map is based on computer modelling of simulated breaches at specific locations. Each breach has been modelled individually and the results combined to create this map. Multiple breaches, other combinations of breaches, different sized tidal surges or flood flows may all give different results. The map only considers the consequences of a breach, it does not make any assumption about the likelihood of a breach occurring. The likelihood of a breach occurring will depend on a number of different factors, including the construction and condition of the defences in the area. A breach is less likely where defences are of a good standard, but a risk of breaching remains. General Enquiries No: Weekday Daytime calls cost 5p plus up to 6p per minute from BT Weekend Unlimited. Mobile and other providers charges may vary Northern Area Tidal Breach Hazard Mapping Map Centred on TF This map is reproduced by permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office. Crown copyright. All rights reserved. Environment Agency , Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.

39 Max Hazard Max Depth Max Velocity Kilometres Kilometres Kilometres Modelled Breach Locations - see also the accompanying plan "Location of Modelled Breaches" Max Hazard Max Depth (m) Max Velocity (m/s) (Flood Risk to People : FD2320) Less than 0.75 (Low Hazard) Between 0.75 and 1.25 (Danger for Some) Date Printed Between 1.25 and 2.0 (Danger for Most) Greater than 2.0 (Danger for All) October 2013 Scenario year Scenario Annual Chance % (1 in 1000) This map shows the level of flood hazard to people (called a hazard rating) if our flood defences are breached at certain locations, for a range of scenarios. The hazard rating depends on the depth and velocity of floodwater, and maximum values of these are also mapped. The map is based on computer modelling of simulated breaches at specific locations. Each breach has been modelled individually and the results combined to create this map. Multiple breaches, other combinations of breaches, different sized tidal surges or flood flows may all give different results. The map only considers the consequences of a breach, it does not make any assumption about the likelihood of a breach occurring. The likelihood of a breach occurring will depend on a number of different factors, including the construction and condition of the defences in the area. A breach is less likely where defences are of a good standard, but a risk of breaching remains. General Enquiries No: Weekday Daytime calls cost 5p plus up to 6p per minute from BT Weekend Unlimited. Mobile and other providers charges may vary Northern Area Tidal Breach Hazard Mapping Map Centred on TF This map is reproduced by permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office. Crown copyright. All rights reserved. Environment Agency , Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.

40 Max Hazard Max Depth Max Velocity Kilometres Kilometres Kilometres Modelled Breach Locations - see also the accompanying plan "Location of Modelled Breaches" Max Hazard Max Depth (m) Max Velocity (m/s) (Flood Risk to People : FD2320) Less than 0.75 (Low Hazard) Between 0.75 and 1.25 (Danger for Some) Date Printed Between 1.25 and 2.0 (Danger for Most) Greater than 2.0 (Danger for All) October 2013 Scenario year Scenario Annual Chance % (1 in 200) This map shows the level of flood hazard to people (called a hazard rating) if our flood defences are breached at certain locations, for a range of scenarios. The hazard rating depends on the depth and velocity of floodwater, and maximum values of these are also mapped. The map is based on computer modelling of simulated breaches at specific locations. Each breach has been modelled individually and the results combined to create this map. Multiple breaches, other combinations of breaches, different sized tidal surges or flood flows may all give different results. The map only considers the consequences of a breach, it does not make any assumption about the likelihood of a breach occurring. The likelihood of a breach occurring will depend on a number of different factors, including the construction and condition of the defences in the area. A breach is less likely where defences are of a good standard, but a risk of breaching remains. General Enquiries No: Weekday Daytime calls cost 5p plus up to 6p per minute from BT Weekend Unlimited. Mobile and other providers charges may vary Northern Area Tidal Breach Hazard Mapping Map Centred on TF This map is reproduced by permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office. Crown copyright. All rights reserved. Environment Agency , Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.

41 Max Hazard Max Depth Max Velocity Kilometres Kilometres Kilometres Modelled Breach Locations - see also the accompanying plan "Location of Modelled Breaches" Max Hazard Max Depth (m) Max Velocity (m/s) (Flood Risk to People : FD2320) Less than 0.75 (Low Hazard) Between 0.75 and 1.25 (Danger for Some) Date Printed Between 1.25 and 2.0 (Danger for Most) Greater than 2.0 (Danger for All) October 2013 Scenario year Scenario Annual Chance % (1 in 1000) This map shows the level of flood hazard to people (called a hazard rating) if our flood defences are breached at certain locations, for a range of scenarios. The hazard rating depends on the depth and velocity of floodwater, and maximum values of these are also mapped. The map is based on computer modelling of simulated breaches at specific locations. Each breach has been modelled individually and the results combined to create this map. Multiple breaches, other combinations of breaches, different sized tidal surges or flood flows may all give different results. The map only considers the consequences of a breach, it does not make any assumption about the likelihood of a breach occurring. The likelihood of a breach occurring will depend on a number of different factors, including the construction and condition of the defences in the area. A breach is less likely where defences are of a good standard, but a risk of breaching remains. General Enquiries No: Weekday Daytime calls cost 5p plus up to 6p per minute from BT Weekend Unlimited. Mobile and other providers charges may vary Northern Area Tidal Breach Hazard Mapping Map Centred on TF This map is reproduced by permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office. Crown copyright. All rights reserved. Environment Agency , Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.

42 Max Hazard Max Depth Max Velocity Kilometres Kilometres Kilometres Max Hazard (Flood Risk to People : FD2320) Less than 0.75 (Low Hazard) Between 0.75 and 1.25 (Danger for Some) Between 1.25 and 2.0 (Danger for Most) Greater than 2.0 (Danger for All) Date Printed October 2013 Max Depth (m) Scenario year Max Velocity (m/s) Scenario % (1 in 200) The map is based on computer modelling of simulated overtopping of the main coastal defences for specific tidal scenarios. t does not include overtopping along the following tidal rivers which are currently being investigated: Witham Haven (upstream of Hobhole), and Welland (upstream of Fosdyke Bridge) The map only considers the consequences of overtopping of the defences, and does not show the possible consequences of breaches of the tidal defences. Separate maps of the flood extent from just breaching of the defences are available. For future climate change scenarios it is assumed that defences remain at 2006 heights. These maps do not replace the flood zone maps used in Planning Policy Statement 25 (PPS25). Please contact the Environment Agency for information on how these maps are used in the management of flood risk. General Enquiries No: Weekday Daytime calls cost 5p plus up to 6p per minute from BT Weekend Unlimited. Mobile and other providers charges may vary Northern Area Tidal Overtopping Hazard Mapping Map Centred on TF This map is reproduced by permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office. Crown copyright. All rights reserved. Environment Agency , Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.

43 Max Hazard Max Depth Max Velocity Kilometres Kilometres Kilometres Max Hazard (Flood Risk to People : FD2320) Less than 0.75 (Low Hazard) Between 0.75 and 1.25 (Danger for Some) Between 1.25 and 2.0 (Danger for Most) Greater than 2.0 (Danger for All) Date Printed October 2013 Max Depth (m) Scenario year Max Velocity (m/s) Scenario % (1 in 1000) The map is based on computer modelling of simulated overtopping of the main coastal defences for specific tidal scenarios. t does not include overtopping along the following tidal rivers which are currently being investigated: Witham Haven (upstream of Hobhole), and Welland (upstream of Fosdyke Bridge) The map only considers the consequences of overtopping of the defences, and does not show the possible consequences of breaches of the tidal defences. Separate maps of the flood extent from just breaching of the defences are available. For future climate change scenarios it is assumed that defences remain at 2006 heights. These maps do not replace the flood zone maps used in Planning Policy Statement 25 (PPS25). Please contact the Environment Agency for information on how these maps are used in the management of flood risk. General Enquiries No: Weekday Daytime calls cost 5p plus up to 6p per minute from BT Weekend Unlimited. Mobile and other providers charges may vary Northern Area Tidal Overtopping Hazard Mapping Map Centred on TF This map is reproduced by permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationary Office. Crown copyright. All rights reserved. Environment Agency , Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.

44 Gee, Anna From: Stokes, Matthew G. Sent: 15 October :04 To: Gee, Anna Subject: FW: Flood risk mitigation - South West Boston - Tytton Lane From: Morris, Debbie [mailto:debbie.morris@environment-agency.gov.uk] Sent: 14 October :06 To: Stokes, Matthew G. Cc: Paul Edwards Subject: RE: Flood risk mitigation - South West Boston - Tytton Lane Matt Thank you for your enquiry. We do not have a specific position on the use of large scale ground raising in the tidal floodplain and are content to be led by the evidence. Any such proposal would need to be accompanied by detailed information and data that demonstrated that flood risk was not significantly increased to third parties as a result of these works. It is likely that, as a minimum, you would need to rerun a hydraulic model to understand the change in hazard, depths and velocities of a tidal breach around any development platform in the floodplain, over the lifetime of the development. Single storey development should consider the 0.1% future scenario for establishing a suitable finished floor level and development proposals that do not include ground floor sleeping can use the 0.5% scenario, over the lifetime of the development. I would strongly recommend that you discuss such proposals with the planning authority, Black Sluice Internal Drainage Board and Lincolnshire County Council Highways over their views on such mitigation measures, before investing in the preparation and provision of suitable evidence. These authorities will have differing areas of focus for consideration, such as SuDs, impacts on pluvial pathways and local drainage etc. If you want to pursue the purchase of our tidal model, please let me know and I can arrange for likely costs to be identified; you would then need to engage a consultant to rerun this model with your development platform included. If you have any further queries, please do not hesitate to contact me. Kind regards Debbie Morris Coastal Partnerships & Strategic Overview Advisor Environment Agency, Anglian Region, Northern Area Guy Gibson Hall, Manby Park, Louth, LN11 8UR ext: int: debbie.morris@environment-agency.gov.uk We continually want to improve our service to you. Please tell us how we did. (5 = good, 1 = poor, n/a = non applicable) 1) Were you happy with the Timeliness of our service? 2) Was our Information / advice clear and relevant? 1

45 3) Was our service Professional? 4) Did we have a friendly and polite Attitude? 5) Overall did you get the right Result from us? Any other comments? Floods happen. Be prepared. Check if you are at risk from flooding and sign up for FREE flood warnings. From: Stokes, Matthew G. [mailto:matthew.stokes@aecom.com] Sent: 09 October :21 To: Morris, Debbie Cc: hall.design@btinternet.com Subject: Flood risk mitigation - South West Boston - Tytton Lane Good Afternoon Debbie I have just called your office but I understand you are away until Friday. I have been given your name as the Partnership & Strategic Overview Officer for the South West Boston site (attached is draft masterplan) which I have recently requested Hazard Mapping data for and am awaiting delivery. I also understand you provided comments on the attached planning proposal letter. My query is regarding the required flood mitigation options for the site. Your planning proposal letter states: The minimum level of mitigation necessary must ensure that the consequences of flooding are adequately managed to the development, taking account of the vulnerability of the future users. Therefore in this hazard category, given the future depths, proposals must be a minimum 2 storey with no ground floor habitable accommodation. The first floor living accommodation shall be above the highest predicted flood depth. The applicant is advised to refer to the following document for information on flood resilience and resistance techniques Improving Flood Performance of New Buildings - Flood Resilient Construction (Department for Communities and Local Government 2007). As we are at the master-planning stage we are currently looking at all potential options for flood mitigation including the use of 2 or 3 storey developments as you request above and the idea of ground raising across the site (by the order of 1 2m) has been raised. As the EA have not stated in the letter their stance on ground raising on the site I would welcome your thoughts. Ground raising has been raised as a possibility to vary residential development type across the site as the ground would be raised above the predicted breach depth and also to aid the design of drainage infrastructure across the site. As stated above I would welcome your thoughts on this. Kind regards Matt Matthew Stokes Senior Flood Risk Consultant D +44 (0) Mob +44 (0) matthew.stokes@aecom.com AECOM 2 City Walk, Leeds, LS11 9AR T +44 (0) F +44 (0)

46 This is confidential and is for the intended recipient only. If you are not the intended recipient, please contact the author and you must not disclose or use the contents in any way. The author bears responsibility for any legal action or disputes arising from views or professional advice expressed which do not relate to the business of AECOM Ltd. AECOM Limited Registered in England No: Registered Office: AECOM House, Victoria Street, St Albans, Herts, AL1 3ER Please consider the environment before printing this Find out more about ONE, AECOM s global e-magazine This message has been scanned and no issues discovered. 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 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. 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. 3

47 Our ref: CCN Your ref: Date: 11 February 2014 Dear Mr Stokes Provision of Products 5, 7 & 8 for Tytton Lane, Boston. Thank you for your request of 13 th January 2014 to use Environment Agency data, Product 5, 7 & 8, in the development of the Flood Risk Assessment (FRA) for the above site. The information is attached. If you have requested this information to help inform a development proposal, then you should note the detail in the attached advisory text on the use of Environment Agency Information for Flood Risk Assessments. Product 5 & 7 Breach Model Due to the size of the Northern Area Tidal Breach Model for W29 and the associated report, the information has been uploaded to our Data Share website. The link to download the information can be found in the accompanying . Product 8 - Hazard Mapping Breaching Enclosed with this letter is a plan showing the location of the breaches we have modelled, together with four plans showing the maximum values of flood depth, velocity and hazard rating (danger to people) for the following scenarios: Year % (1 in 200) chance event Year % (1 in 1000) chance event Year % (1 in 200) chance event Year % (1 in 1000) chance event Product 8 - Hazard Mapping Overtopping Please find enclosed two plans showing the maximum values of flood depth, velocity and hazard rating (danger to people) resulting from simulated overtopping of defences. The plans show data for the following scenarios: Year % (1 in 200) chance event Year % (1 in 1000) chance event Your site is not affected by overtopping for the present day (2006) scenarios. Contd / Waterside House, Waterside North, Lincoln, LN2 5HA Customer services line: enquiries@environment-agency.gov.uk Weekday Daytime calls cost 5p plus up to 6p per minute from BT Weekend Unlimited. Mobile and other providers charges may vary

48 Please note that the modelling completed to date, and hence the overtopping represented on the maps, does not include overtopping along the following tidal rivers: Witham Haven (upstream of Hobhole) and Welland (upstream of Fosdyke Bridge). It is important that you read the contextual notes on the maps. This information is provided subject to the enclosed license, which you should read. If you have any queries or would like to discuss the content of this letter further please contact Clare Fravigar using the telephone/ details below. Please quote our CCN reference number in all correspondence where data is referenced, including the Flood Risk Assessment. Yours sincerely Clare Fravigar Modelling and Hydrology Team Direct dial Direct fax Direct Enc. FRA Advisory Text Breach Location Plan Breach Hazard Maps x 4 Overtopping Hazard Maps x 2 License CaVMID W29 Report 2

49 Gee, Anna From: Paul Edwards Sent: 09 October :16 To: Gee, Anna Cc: Christopher Holliday Subject: Sequential test...sw Boston Chestnuts new football ground & etc Dear Anna, Further to your mails of 27 and 30 September. Agents acting for Chestnuts (Signet Planning) now have a copy of the EA letter of response to the pre-app process that has started to engage with statutory consultees. The EA letter is dated 25 September Clearly, with all the other sequential tests that will become necessary, I have tried to restrict my comments to the flood risk tests. I appreciate and would caution that the case for enabling development and any future queries about opportunities for disaggregation are likely to follow but that I expect might be part of the applicants case over the uniqueness of the package and its requisite parts. I am grateful for the opportunity to give you some advice since it is the responsibility of the applicant to provide all of the necessary evidence so that the lpa can apply the sequential test. I would add at this stage, and without prejudice to any future decision of the local planning authority, that the EA response is clearly from a consultee and may not represent the opinion or decision of the lpa at this time: I will however respond to your bulleted points in the order in which you raised them: The hazard mapping information referred to by the Agency in their letter is, as I understand, a finer level of detail than our own SFRA and it would be these datasets that I would expect you to use to inform the FRA. The Council s SFRA, confirms that all of the lands identified on the Dwg No TLB/-09 are within the Danger for All hazard category but clearly the EA data might enable judgements over a refined sequential test within the sites. The SFRA shows the entire land as at Medium tidal flood probability. Housing. The sequential test with respect to the housing element.. given that this is the highest level of vulnerability classification (more vulnerable), is significantly influenced by the agreed fact that presently the Borough does not have a five year supply of housing land. Local Plan housing Policy H1 is the only specific saved supply policy. However, there are no local plan allocations remaining that have not been built or commenced which can be pointed to in order to show the availability of housing land. In any event since we do not have a five year supply, we have taken the view (NPPF) that H1 must be considered to be out of date. Thus the view we have taken, and to which the EA subscribes, is that local plan allocations cannot assist in seeking sequentially preferable sites. You may wish to look at the SFRA, since it refines the EA data on probability contained in the flood zone maps. Clearly the Exception Test will be necessary for the housing proposals. Although some not insignificant consents have been given over the past 18 months which we believe are available these, nevertheless have not met the supply deficit. Monthly monitoring of the 5-year supply of housing land is now available on the Council s website so that this information is always available to the public. 1

50 The other area which could potentially assist the Sequential Test, in the absence of any allocated sites, is the SHLAA. However, at this point in time, the SHLAA sites have not been assessed or graded to pick out preferences or levels of suitability or availability. It is also unlikely that this exercise would be able to be referred to for at least 6 months. In any event, we take the view that a SHLAA proposal, mooted by a land owner will not have any material weight in terms of a sequentially preferable site until it is a proposed allocation as part of an emerging plan rather than remaining only in a SHLAA. The emerging South East Lincs Local Plan (SELLP) Strategies and Policies DPD Full Consultation contains broad locations for housing growth but the subject site does not feature specifically. Retail. Defined as less vulnerable. The only allocated site (Policy RTC1) in the Boston inset map to the Plan that has not been developed is the Wide Bargate/Red Lion Street site (B/09/0190). The principal retail policies in the local plan were not saved and in any event for retailing purposes we are likely to consider that the 1999 retail policies are not up to date with either the former PPS6 or the NPPF. The EA hazard mapping shows this site at generally a lower hazard rating but it has a High Tidal flooding probability (as assessed in the SFRA). Thus this site appears to have a higher risk but a lower probability than your subject site. However, the last application for retail development on this site was refused over reasons of access and, in any event we believe that this is unlikely to be a suitable site for convenience retailing on the basis that the A16 retail site is anchored by a food superstore (7,000 sq m). I am not aware of any other allocated retail sites or sites that are large enough that might satisfy the Flood Risk Sequential Test, clearly the RIA sequential test is something else. Also, at some point the question of disaggregation might come up. Thus, I am not able to point to a likely retail site that is either sequentially more preferable and reasonably available than the subject site that can carry any weight in terms of a consent, an existing or an emerging allocation. The preferred Policy option in the SELLP is for a hierarchy of centres focusing retail on larger settlements and the NPPF default threshold for retail impact assessment of 2,500 sq m would apply. Commercial. These areas have been identified for pub/restaurant/ drive through /hotel. Other than hotel, these are all less vulnerable with the hotel being a residential use vulnerability which will require the Exception Test.. There is an outline hotel approval on Swineshead Road B/12/0163 which is mixed hazard Danger for All and for Most. I do not see and I am not aware of any other live hotel consents that are still capable of implementation or a site that may be reasonably available. A larger outline was give at the Enterprise Park at Boardsides that included a hotel but the undeveloped parts of that area (not under that outline) appear to be in the same hazard category as the subject site. Assembly & Leisure. There are, as you might expect, no other allocations or sites for uses of this scale that I can refer you to. I suspect that other proposals for this type of development would only come forward as part of a larger scheme which might incorporate elements of enabling development and thus local plan documents are silent on a 13 acre site for stadia or community/recreation uses. The SE Lincs Joint Sports Provision and Open Space Assessment which is informing the SELLP shows an extra need to 2031 (of probable relevance here) for 1.5 sports hall, 1 synthetic turf pitch, 6.5 adult football pitches and 7 junior pitches. The overall policy option is likely to be an approach that seeks to ensure that all sections of the community have access to high quality open space and opportunities for sport; although sustainable principles tell us that they should be close to town centres and main centres of population. A football ground, we can accept does raise particular land use planning challenges and there will be a balance between accessibility for a wider community and accessibility at this location by means other than the private car. I cannot therefore assist in terms of other reasonably available sites. 2

51 The search area for the sequential test sites depends I think on local circumstances and the likely catchment for the category of development that is being proposed. This is reflected in the PPS25 Practice Guidance and the National Planning Practice Guidance. Para 4.18 of the PPS Practice Guidance refers to circumstances where sites outside Zones 2 & 3 may not be reasonable alternatives. Thus the area of search for the stadium will clearly be a wider area than for commercial uses and on the face of it a view could be taken that the catchment of the stadium will be as large as or even beyond the local authority boundary (or boundaries to cover SELLP area). Your clients might have information on the spread of season ticket holders or any other catchment/ post code data they might have. I think the comments above have already addressed the area of search for the other elements..based upon the likely existence of reasonably available alternative sites but since the current local plan does not envisage a sports stadium I can only suggest that the area of search is district wide. I have looked for assistance in the former Regional Strategy to see if it had anything to say on sub regional sport and recreation need. It does not specifically say anything that might help..other than there being adequate provision for sports and recreation facilities. You might wish to seek advice from Sports England and/or the Football Association in terms of catchments to justify an area of search.. I conclude, as a minimum, it should be district wide and I see at para 4.27 to the PPS Guidance that the evidence for a sequential test can include how the exception test will be applied. Although the Exception test is not relevant for the stadium use per se..as part of the wider package and the applicants likely case about the need and enabling development, it may be that the wider sustainability benefits for the community might feature in support of the sequential test. The EA Standing Advice version 3.1 dated April 2012 on the Sequential test might be worth consulting although I do appreciate it is potentially out of date. Your third bullet has already been addressed I cannot suggest any specific search criteria other than that which I have referred to above. You will see that I have copied this to Mr Millbank at the EA who replied to the pre-app exercise, so that we are all kept informed over our actions for such a development of this scale and to continue close working. I trust that this is of assistance but naturally please do not hesitate to contact me when or if you require anything further. Paul Edwards Development Control Manager Tel: To keep up to date with Council information please sign up to the electronic Boston Bulletin by sending your address to graphics.unit@boston.gov.uk with Boston Bulletin in the subject box. We can provide this information in other languages and formats for example, in large print, in Braille, CD or audio cassette or cd. Please telephone for this service. This may contain sensitive or personal data, please think before including in any forwarded correspondence. The information within this is confidential. It is intended solely for the addressee and access to this by anyone else is unauthorised. Such unauthorised use, disclosure, copying, distribution, any action or inaction in reliance of it is strictly prohibited and may be unlawful. If you have received this in error: 1. notify the sender immediately; 3

52 2. do not use or disclose the information in any way; and 3. delete the from your system. Think about the environment. Only print this if you need to. 4

53 Gee, Anna From: planning Sent: 30 September :25 To: Gee, Anna Subject: RE: Sequential Test - Request for guidance Dear Anna, I have forwarded your query onto Paul Edwards, our Development Control Manager who advises that he is currently dealing with Pre Application Advice for this site and is happy to respond to any of your queries directly, he can be contacted on paul.edwards@boston.gov.uk. In respect of specific data sets for this site, you are advised to contact Annette Hewitson at the Environment Agency, the number for that office is Kindest regards, Melissa Phillips Planning Services Support Assistant T: F: E: planning@boston.gov.uk You should be aware that the above is my opinion only and is made without prejudice to any future decision made by Boston Borough Council. It relates only to Planning and does not cover any other acts or legislation. From: Gee, Anna [mailto:anna.gee@aecom.com] Sent: 27 September :31 To: planning Subject: Sequential Test - Request for guidance To whom it may concern, AECOM have been commissioned to undertake a Sequential Test for a proposed mixed use development on a site in South West Boston and as such require some guidance from within Boston Borough Council. The site is located to the south of Tytton Lane in Wyberton, Boston and the proposed development comprises residential and commercial units, along with the erection of a new football stadium. The Sequential Test is being undertaken to inform the master-planning stage prior to undertaking the required flood risk assessment. Specific guidance that we require from yourselves is as follows; Guidance on the application of the Sequential Test within Boston and datasets to be used primarily as the majority of Boston is within Flood Zone 3; Confirmation of the search area within which the Sequential Test should be carried out for the different elements of the development, i.e. residential, commercial and football stadium; Known potential development sites that should be considered or, direction as to where to locate sites for assessment; and Any specific search criteria that is required by Boston Borough Council for the different planning elements. If you have any questions regarding this request please don t hesitate to contact me. Kind Regards, 1

54 Anna Anna Gee BSc (Hons) MSc Graduate Flood Risk Consultant D +44 (0) anna.gee@aecom.com AECOM 2 City Walk, Leeds, LS11 9AR T +44 (0) F +44 (0) This is confidential and is for the intended recipient only. If you are not the intended recipient, please contact the author and you must not disclose or use the contents in any way. The author bears responsibility for any legal action or disputes arising from views or professional advice expressed which do not relate to the business of AECOM Ltd. AECOM Limited Registered in England No: Registered Office: AECOM House, Victoria Street, St Albans, Herts, AL1 3ER Please consider the environment before printing this Find out more about ONE, AECOM s global e-magazine To keep up to date with Council information please sign up to the electronic Boston Bulletin by sending your address to graphics.unit@boston.gov.uk with Boston Bulletin in the subject box. We can provide this information in other languages and formats for example, in large print, in Braille, CD or audio cassette or cd. Please telephone for this service. This may contain sensitive or personal data, please think before including in any forwarded correspondence. The information within this is confidential. It is intended solely for the addressee and access to this by anyone else is unauthorised. Such unauthorised use, disclosure, copying, distribution, any action or inaction in reliance of it is strictly prohibited and may be unlawful. If you have received this in error: 1. notify the sender immediately; 2. do not use or disclose the information in any way; and 3. delete the from your system. Think about the environment. Only print this if you need to. 2

55 Gee, Anna From: Andrew Scott Sent: 14 October :30 To: Gee, Anna Cc: Ian Warsap Subject: RE: Website Enquiry Attachments: AECOM.pdf; FX1050.pdf; FX1051.pdf Hi Anna. Please find attached some plans showing the Boards watercourses at the locations requested. I have included an overview of the area to show where the water flows either under gravity or during pump operations. You will note that with reference your enquiry regarding the flow of the Wyberton Towns Drain at the Tytton Lane East development that water can flow in either direction. I have indicated culverts on the smaller plans to show locations. Please be aware that the Board does not own these culverts, and it is assumed that any culverts under roads will be the responsibility of Lincolnshire County Council Highways. The Board is merely responsible for the maintenance of the channel through which water flows. All watercourses marked in blue, or blue and yellow dashes, are watercourses vested to the Board for all maintenance and/or improvement under the Land Drainage Act A rolling schedule of maintenance of Board watercourses continues throughout the year, and includes the removal of vegetation during the summer/autumn, and the de-silting of selected watercourses during winter. All other water courses, marked light blue, are regarded as private or riparian watercourses. These are the responsibility of the adjacent land or property owners. The Board has supervisory responsibility for these watercourses, and offers advice regarding maintenance & upkeep. Discharge of any water into any watercourse requires full written consent from the Board. You will be aware that legislation is due in the coming year regarding the use of Sustainable Drainage Systems (SuDS) in all future developments. The Board has a standard requirement that any discharge into its systems should be a rate of no more than 1.41 ltrs/sec/ha this is the current greenfield run-off rate, and is set against the pumping capacity of the Boards numerous pumping stations across its district. Any discharge above this rate will be subject to a development fee which will be used by the Board to make any necessary improvements to its watercourses to accept the additional flows. You should also see Section 23 of the Land Drainage Act 1991 this prohibits the obstruction of any watercourse without the consent of the relevant IDB. There are numerous Board and private watercourses across both sites indicated, and if any of these (in particular private watercourses) are to be piped or filled, then consent will be required from the Board. The loss of any existing volume storage capacity will need to be considered, and provision included to the Boards satisfaction, in any future surface water drainage scheme. All Board watercourses have various byelaws which pertain to them, in particular Byelaw No 3 regarding the discharge of water, and Byelaw 10 regarding the siting of structures with 9 metres distance of a Board watercourse. Please advise any potential clients that no structures will be permitted within 9 metres of a Boards open or piped watercourse. A summary of the Boards Byelaws can be found here: There is a link at the top of the page for full details of the byelaws if required. A hard copy is available on request. There have been no recent or historical instances of flooding of the areas requested. 1

56 If you require any further information, please do not hesitate to contact me. Kind regards. Andy Scott Planning & Enforcement Officer Black Sluice IDB Tel: From: Gee, Anna Sent: 10 October :11 To: Andrew Scott Subject: RE: Website Enquiry Hi Andy, I was just wondering whether you have had the opportunity to look into my enquiry below? Many thanks, Anna From: Andrew Scott [mailto:andrew.scott@blacksluiceidb.gov.uk] Sent: 02 October :13 To: Gee, Anna Subject: RE: Website Enquiry Hi Anna. With regards to both sites, I can certainly provide you with plans showing our maintained watercourses, but it won t be until next week as I m a bit eyeballs out at the moment. Thanks. Andy Scott Planning & Enforcement Officer Black Sluice IDB Tel: From: Gee, Anna [mailto:anna.gee@aecom.com] Sent: 02 October :32 To: Andrew Scott Subject: RE: Website Enquiry Hi Andy, Thanks for getting back to me so quickly. Please find attached a site location map (Grid Ref: TF ) and also the proposed layout for the site at Tytton Lane (Appendix 3). On a related note, whilst Tytton Lane is our priority at this point, we are also carrying out an extremely high level assessment of another site in the area known as the South West Quadrant (Site map attached, Grid Ref: TF

57 4270 ). As such if you come across any information that might be of relevance to this site whilst looking for information regarding Tytton Lane that you would be able to pass it on I would be grateful. If you require any further information please let me know. Many thanks, Anna From: Andrew Scott [mailto:andrew.scott@blacksluiceidb.gov.uk] Sent: 02 October :15 To: Gee, Anna Subject: RE: Website Enquiry Hi, Anna. Regarding your below, could you please provide a map showing the location of the site, so that I may provide you with the relevant information regarding the Boards watercourses. Please be aware that all flood mapping requests, including modelled flood levels, are to be made via the Environment Agency. Kind regards. Andy Scott Planning & Enforcement Officer Black Sluice IDB Tel: From: Gee, Anna [mailto:anna.gee@aecom.com] Sent: 01 October :15 To: TempUser Subject: Website Enquiry To whom it may concern, I am contacting you regarding a Flood Risk Assessment that AECOM have been commissioned to carry out for a large mixed use development site within the Black Sluice IDB area. As such we require some high level information about the drains in the area that I am hoping you are able to provide. As mentioned above the site is proposed for a mixed use development and is located immediately south of Tytton Lane East in Wyberton, South West Boston (TF ). The information required from the site is as follows: Information about the drains that run through the site itself, specifically any historical incidences of flooding and general information about the maintenance of these drains Information about Towns Drain which borders the southern extent of the proposed site, in particular historical incidences of flooding, maintenance of this drain and confirmation of the direction of flow and where it discharges into (South Forty Foot Drain?) Any further information about the drains in the vicinity of the site, for example modelled flood levels. If you have any questions please don t hesitate to contact me. I look forward to hearing from you. Kind Regards, Anna Gee 3

58 Anna Gee BSc (Hons) MSc Graduate Flood Risk Consultant D +44 (0) anna.gee@aecom.com AECOM 2 City Walk, Leeds, LS11 9AR T +44 (0) F +44 (0) This is confidential and is for the intended recipient only. If you are not the intended recipient, please contact the author and you must not disclose or use the contents in any way. The author bears responsibility for any legal action or disputes arising from views or professional advice expressed which do not relate to the business of AECOM Ltd. AECOM Limited Registered in England No: Registered Office: AECOM House, Victoria Street, St Albans, Herts, AL1 3ER Please consider the environment before printing this Find out more about ONE, AECOM s global e-magazine 4

59 Chain Bridge ") Cook's Lock ") ± South West Quadrant Tytton Lane East Water may flow in both directions here Kirton & Frampton Cartchment Legend BSIDB Open Drains BSIDB Piped Drains ") Pumping Stations Boundary of District EA Watercourses Wyberton Marsh Catchment Black Sluice Internal Drainage Board Station Road, Swineshead, Boston, Lincolnshire PE20 3PW Tel: Crown Copyright and database right All rights reserved. Ordnance Survey Licence number Date: Wyberton Marsh ") General Overview of BSIDB Drains & Catchments October 2013 Scale: 1:25,000

60 !R!R!R!R FX1050!R!H!H!H!R!H!R!R!R!R!R!R!R!H!H!.!.!R!R ±!H!R!R!R!R!R!H!R!H!H!H F L O W!R!R!H Legend!R BSIDB Open Drains BSIDB Piped Drains!H BSIDB/LCC Culverts Private Watercourses!R!R Proposed development!r!h!h!r!r!h!h!h!h Black Sluice Internal Drainage Board Station Road, Swineshead, Boston, Lincolnshire PE20 3PW Tel: mailbox@blacksluiceidb.gov.uk Disclaimer:Flow arrows shown next to BSIDB Watercourses are deemed to show correct flow direction - flow arrows next to Private Watercourses are assumed only, and should not be taken as accurate. BSIDB Watercourses - Tytton Lane East, Boston!R Crown Copyright and database right All rights reserved. Ordnance Survey Licence number Date: October 2013 Scale: 1:5,000

61 Appendix C Tidal Breach Modelling AECOM TIDAL BREACH MODELLING OUTPUTS Drawing No. 1 Draft 200 Year Depth (2006) Drawing No. 2 Draft 200 Year Hazard (2006) Drawing No. 3 Draft 200 Year Depth Plus Climate Change (2115) Drawing No. 3a Draft 200 Year Depth Plus Climate Change (2115) Spot Heights Drawing No. 4 Draft 200 Year Hazard Plus Climate Change (2115) Drawing No. 9 Draft 200 Year Depth Plus Climate Change (2115) Development Platform Scenario:001 Drawing No. 10 Draft 200 Year Hazard Plus Climate Change (2115) Development Platform Scenario:001 Drawing No. 13 Draft 200 Year Depth Plus Climate Change (2115) Development Platform Scenario:002 Drawing No. 14 Draft 200 Year Hazard Plus Climate Change (2115) Development Platform Scenario:002 Drawing No. 25 Draft 200 Year Depth Plus Climate Change (2115) Development Platform Scenario: 003 Drawing No. 26 Draft 200 Year Hazard Plus Climate Change (2115) Development Platform Scenario: 003

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