Hedon Haven Evidence Base

Baseline Flood Risk Study

4706 2982 September 2013

Prepared for: East Riding of Council

UNITED KINGDOM & IRELAND

East Riding of Yorkshire Council Haven Evidence Base

REVISION SCHEDULE

Rev Date Details Prepared by Reviewed by Approved by

1 July 2012 Draft Richard James Elizabeth Young Kirsty Cobb Consultant Senior Consultant Associate

2 September Final Richard James Elizabeth Young Kirsty Cobb 2012 Consultant Senior Consultant Associate

3 September Final with revisions Richard James Elizabeth Young Neil Stephenson 2013 Consultant Senior Consultant Technical Director

URS WestOne Wellington Street LS1 1BA

0113 204 5000

Hedon Haven Baseline Study September 2013 Flood Risk Council Hedon Haven Evidence Base

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Hedon Haven Baseline Study September 2013 Flood Risk East Riding of Yorkshire Council Hedon Haven Evidence Base

Contents

1 Introduction ...... 1 1.1 Land at Hedon Haven ...... 1 2 Methodology ...... 2 2.1 Scope of Study ...... 2 2.2 Sources of Information/ Data ...... 2 3 Baseline Conditions ...... 4 3.1 Potential Sources of Flooding ...... 4 3.2 Tidal Flooding ...... 4 3.3 Fluvial Flooding ...... 11 3.4 Groundwater Flooding ...... 14 3.5 Surface Water Flooding ...... 15 3.6 Limitations or Difficulties ...... 17 4 Future Considerations for Development ...... 18 5 Conclusions ...... 24 6 References ...... 27

Figures Figure 1: Site Location Plan Figure 2: EA Indicative Flood Zone Map Figure 3: Watercourse and Flood Defence Map Figure 4: 2007 Historic Flood Outline Figure 5: Overtopping Scenario – 0.5% AEP (2010) Figure 6: Overtopping Scenario – 0.5% AEP (2115) Figure 7: Breach Scenario at Holme – 0.5% AEP (2010) Figure 8: Breach Scenario at – 0.5% AEP (2010) Figure 9: Breach Scenario at Paull Holme – 0.5% AEP (2115) Figure 10: Fluvial Flood Mapping Figure 11: Indicative Surface Water Flood Hazard

Appendix Appendix A: Site Photograph Log

Hedon Haven Baseline Study September 2013 Flood Risk East Riding of Yorkshire Council Hedon Haven Evidence Base

1 Introduction

1.1 Land at Hedon Haven

1.1.1 The land at Hedon Haven considered in this report predominantly comprises farmland, and is described in Figure 1.

1.1.2 A parcel of land to the south of Salt End, adjacent to the (approximately 80 ha) is allocated for employment uses by the District Wide Local Plan in 1999 (East Riding of Yorkshire Council, 1999). An allocation of up to 240 ha (comprising this parcel and an additional 160ha of land in the surrounding area) to cater for the expansion of the is being considered through the emerging East Riding Local Plan and is referred to as HAV1/2 in the Allocations Document.

1.1.3 A series of baseline environmental studies have been undertaken to inform the emerging East Riding Local Plan Strategy and Allocations Documents, and the supporting Sustainability Appraisal/ Strategic Environmental Assessment and Habitats Regulations Assessment.

1.1.4 This report summarises the flood risk baseline information in relation to the site.

1.1.5 For ease of reference, the 240 ha site associated with the proposed Policy HAV1/2 allocation is subdivided within this report as follows (see Figure 1):

• Paull part of the site (i.e. the HAV1 element of the allocation). • Hedon Haven North part of the site (i.e. part of the HAV2 element of the allocation); and, • Hedon Haven South part of the site (i.e. the remaining part of the HAV2 element of the allocation)

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2 Methodology

2.1 Scope of Study

2.1.1 The general objectives of this study were to:

• undertake a site visit to observe and take a photographic log of watercourses, drains and other water features on the site, in addition to defences, tidal barriers and outfalls; • review existing information relating to the flood risk posed to the site, from all sources (including fluvial, tidal, groundwater, surface water and sewer flooding); • consult the Environment Agency, East Riding of Yorkshire Council, Preston Internal Drainage Board and Associated British Ports regarding flood risk to the site and any requirements they may have for future development; and • assess the flood risk to the site under existing and future conditions (taking into account climate change), in accordance with the National Planning Policy Framework (NPPF) (DCLG, 2012) and the East Riding Level 1 Strategic Flood Risk Assessment (SFRA) guidance (Jacobs, 2010)

2.2 Sources of Information/ Data

2.2.1 Table 1 below summarises the information that has informed this baseline study.

Table 1: Sources of information/ data

Aim Data Reviewed Comments

Identification of hydrological Landranger Map features Environment Agency Indicative Identification of tidal inundation Flood Zone Map extents and historical flooding Strategic Flood Risk Assessment Flood risk, defences, historical (SFRA) (Jacobs, 2010) events Modelled water levels from the Environment Agency North Bank Humber North Bank Study and Modelling Study (EA, 2011a) information of flood defences. Identifying the existing Humber Estuary Shoreline Information relating to the flood tidal flood extents and Management Plan (SMP) defences levels Identification of interaction between Infrastructure Study Update the Humber, and surface water drainage NEECA 2 South Holderness Study Information relating to breaching (EA, 2011b) and overtopping of the defences Information on the condition and Humber Flood Risk Management anticipated lifetime of the flood Strategy (EA, 2008) defences Topographic Survey for the Paull Information on ground levels and part of the site flood defence levels

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Aim Data Reviewed Comments

SFRA, EA, Preston Internal Drainage Board, Infrastructure Identification of fluvial flood risk Study Update Information relating to fluvial flood NEECA 2 South Holderness Study modelling and hydrological Identification of flooding catchments from other sources SFRA, EA, Preston Internal Identification of flood risk from Drainage Board, Infrastructure surface water Study Update Identification of flood risk from SFRA, EA, BGS Boreholes groundwater

EA Mapping Identifying historical flood extents

SFRA Historical

Identifying the historical FEH CD-ROM Version 3.0 (IoH, Rainfall data for the calculation of flooding regime 2009) runoff from the site. www.dundee.ac.uk//cbhe Details of previous flood events

News articles about previous Internet Sources flooding events

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3 Baseline Conditions

3.1 Potential Sources of Flooding

3.1.1 There are a number sources of flooding which could potentially impact the site. The Paull part of the site lies adjacent to the Humber Estuary and the EA’s Flood Zone map shows that all three sites lie predominantly within Flood Zone 3 (Figure 2). The Level 1 Strategic Flood Risk Assessment (SFRA) confirms that this area of Flood Zone 3 is tidally dominated.

3.1.2 There are a number of watercourses and drains that traverse the site. Burstwick Drain is a main river that bisects the Hedon Haven North site and the Hedon Haven South part of the site prior to discharging through a tidal barrier on the northern side of the Paull part of the site. This tidal reach of the watercourse is referred to as Hedon Haven prior to its discharge into the Humber Estuary at the western side of the Paull part of the site, as shown in Figure 3.

3.1.3 Reedmere Sewer is an ordinary watercourse that flows east to west across the Hedon Haven North part of the site. In addition to these watercourses all three sites are crossed by a number of land drains.

3.1.4 The site may be at risk from surface water flooding, as indicated by the presence of surface water drains on site, and the risk from groundwater sources is also considered.

3.1.5 The sites are not considered to be at risk from artificial sources including reservoirs and canals as there are none present in the vicinity.

3.2 Tidal Flooding

3.2.1 All three parts of the site lie predominantly within Flood Zone 3 (i.e. a high probability of flooding), as identified within the EA’s Flood Zone map shown in Figure 2. This zoning indicates that the site has a >0.5% annual exceedance probability (AEP) (1 in 200 or greater annual probability) of flooding from the sea (in any given year.

3.2.2 Due to the relatively flat topography of the site, the extent of Flood Zone 2 (i.e. the area of land assessed as having between a 0.5% - 0.1% AEP of tidal flooding (1 in 200 and 1 in 1,000 year) is only marginally larger than the extent of Flood Zone 3.

3.2.3 Two isolated ‘islands’ of Flood Zone 1 are found within the Hedon Haven North part of the site and one small pocket is found within the Hedon Haven South part of the site. Flood Zone 1 corresponds with areas assessed as having a less than <0.1% AEP of river or sea flooding in any year . Cumulatively these areas represent approximately 10.8 ha (4.5%) of the total site area (240 ha).

3.2.4 Owing to the close proximity to the Humber Estuary, the SFRA identifies that the flood zoning in the site is considered to be predominantly associated with tidal sources.

3.2.5 The main rivers and ordinary watercourses on the site ultimately discharge into the Humber Estuary and are therefore likely to be influenced by the tide water levels. A tidal barrier is present on Burstwick Drain which discharges into Hedon Haven. During the site visit on 28th June 2012, it was observed that tidal backflow occurs during low tides. However, according to the SFRA and the EA, at high tides the barrier shuts and results in the tide-locking of Burstwick

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Drain (East Riding of Yorkshire Council, 2011; EA, 2012a). This tide-locking may also prevent the surface water land drains from discharging into the Humber Estuary/ Burstwick Drain.

3.2.6 At present there is no permanent pumping facility at the tidal barrier to pump water over the barrier during high tide; when tide-locking occurs water in Burstwick Drain backs up until the tide has receded. Historically this has been responsible for surface water and sewer flooding incidents in Hedon town and the site area, which is discussed in greater detail in the surface water and fluvial flooding sections.

Historic Tidal Flooding

3.2.7 A significant area of the Paull part of the site was inundated in February 1953 during the 1953 Flood, with the inundation extent demarcated in Figure 4. This event occurred as a combination of a severe European windstorm and high spring tide and it affected locations in the Netherlands, Belgium, and Scotland (National Meteorology Library and Archive, 2011).

3.2.8 The Chronology of British Hydrological Events Flood History Database (Law et al., 2012) does not include any other historical sea flooding events for Hedon or Paull. Several flood events have been recorded in the database alongside the Humber, but none of those recorded specifically mention the site or its surrounding settlements.

3.2.9 According to the EA, around a quarter of the Paull part of the site was flooded in the June 2007 flood event when the local drainage network was over-whelmed.

Flood Defences

3.2.10 According to the EA Flood Zone maps, the sites are not classified as an area benefiting from flood defences. However, it is afforded protection from tidal sources due to the presence of an earth embankment with stone protection on the estuary face, raised high ground and, to a lesser extent, gabion boxes. The tidal defences border the western side of the Paull part of the site along the Humber Estuary and along the southern bank of Hedon Haven to the tidal barrier. Figure 3 shows a location map of these defences and photographs are shown in the picture log in the Appendices.

3.2.11 The EA has provided conceptual defence levels based upon a combination of high resolution LiDAR and survey data for the west/ north-western edges of the Paull part of the site. These conceptual levels range from a minimum elevation of 6.44 m Above Ordnance Datum (AOD) to 7.62 m AOD.

3.2.12 A topographic survey has been undertaken for the Paull part of the site and it shows that the surveyed levels along the defences generally align with the conceptual defence levels provided by the EA; spot heights along the crest of the defences range from a minimum of 6.33 m AOD to a maximum of 7.62 m AOD.

3.2.13 The EA is responsible for the maintenance of all of the flood defences bordering the Paull part of the site and regularly inspect the defences to ensure they are fit for purpose. Data provided by the EA in May 2013 states that the current condition of the adjacent flood defences are all considered to be either 1 (very good) or 2 (good), on a scale of 1 (very good) to 5 (very poor).

3.2.14 The Humber Flood Risk Management Strategy (HFRMS) states that the estuary flood defences were considered to be in good condition at the time of writing in 2008. The document states

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that the defences around Hull (to the west of the Hedon Haven area) were considered to be provide a 0.5% AEP event standard of protection, whilst those around Paull (to the south) provide a standard of protection of up to the 1% AEP event. The HFRMS also states that the defences were anticipated to have a remaining life of 10 to 20 years from when the document was written in 2008.

3.2.15 Following correspondence with the EA between January and March 2013, it is understood that the last structural assessment of the flood defences in the area identified that the anticipated lifetime of the defences along Hedon Haven was 10-20 years. A subsequent visual inspection undertaken on behalf of the EA in 2011 suggested that the lifetime of the defences on the south bank of Hedon Haven may be less than previously assessed (5-10 years).

3.2.16 According to the HFRMS, the proposed management approach is to continue to protect this area. Furthermore, the HFRMS states that work was planned at Paull village to review the risk of waves overtopping the sea wall and flooding adjacent properties, and to carry-out improvements if necessary.

Modelled Flood Levels

3.2.17 The EA has provided modelled water levels for the Humber Estuary for a range of flood return periods, including an allowance for the potential impact of climate change. The modelled levels have been extracted from the Humber Tidal Modelling North Bank study and reflect still water levels for the baseline year of 2010.

3.2.18 Modelled water levels, which take into account climate change, are indicative of the effects of sea-level rise by the year 2115. A 1.125 m increase in sea level was calculated for this time period and is based upon the climate predictions given by the Department for Environment, Food and Rural Affairs (DEFRA) and also presented in the NPPF. This value was added to the 0.5% AEP water level for the baseline year (2010) to project the water levels under 2115 climate conditions.

3.2.19 Relevant modelled water levels are presented with respect to the conceptualised defence levels in Table 1 below. A location map of the model nodes and flood defences is shown in Figure 3.

Table 1: Modelled tidal levels in the Humber Estuary

Return period (years) Model 200 + 1000 + Conceptual Node 10 50 100 200 1000 CC CC defence height

OT 48 4.77 4.95 5.08 5.16 5.34 6.29 6.47 7.62

OT 49 4.77 4.95 5.08 5.16 5.34 6.29 6.47 7.62

OT 50 4.77 4.95 5.08 5.17 5.35 6.3 6.47 6.97

OT 51 4.77 4.96 5.08 5.17 5.35 6.3 6.48 6.44

3.2.20 Assuming the defences are not damaged or breached the information provided on the conceptual defence heights suggests that they could provide protection up to the 0.1% AEP event for 2010 and the 0.5% AEP event plus climate change tidal event for 2115. This standard of protection assumes the correct operation of the tidal barrier on Burstwick Drain.

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3.2.21 The elevation of the banks of Burstwick Drain upstream of the tidal barrier ranges from a minimum of 4.77 m AOD to a maximum of 5.35 m AOD. If the tidal barrier was to fail and tidal waters flowed into Burstwick Drain, the channel may only be able to accommodate the 1 in 10 year tidal flood levels (not accounting for influence of fluvial contribution).

Flood Risk from Overtopping and Breach of Defences

3.2.22 There is a residual risk of flooding as a result of overtopping of and a breach of the flood defences.

3.2.23 The EA commissioned a study to establish the risk of overtopping and breach of the defences along the north bank of the Humber (EA, 2009). The assessment included two-dimensional modelling to determine the risk for different flood return periods for the baseline scenario (for the year 2010) and also taking into account the potential impact of climate change on sea level rise to the year 2115. The sea level rise allowance to the year 2115 is +1.125 m above the 2010 (baseline) levels, as per the recommendations of the Technical Guidance to the NPPF.

3.2.24 The design tide hydrographs used in the EA-commissioned overtopping and breach assessment considered both the astronomical tide and the surge element in accordance with EA and DEFRA guidance. The surge profile was based on the 1953 event on the Humber and the tidal hydrograph was scaled to the design peak water levels (as presented in Table 1).

3.2.25 An additional 0.85 m was added onto the modelled water levels to account for wave heights, with the 0.85 m being equivalent to the 1 in 1 year significant wave height around the Salt End Chemical Works. An increase of 10% was applied to wave heights to represent the impacts of climate change in line with the requirements of the NPPF Technical Guidance.

3.2.26 In order to assess the overtopping of the flood defences, the defence heights were conceptualised based on a combination of LiDAR data and surveys (where available).

Baseline Overtopping Assessment (2010)

3.2.27 The outputs from the defended overtopping assessment (EA, 2011a) show that some areas of the western part of the Paull part of the site, bordering the Humber Estuary and Hedon Haven, could be inundated with flood water from the 0.5% AEP and the 0.1% AEP design events. In both cases the depth of the floodwaters from overtopping is predominantly between 0 and 0.25 m, though isolated areas of depths up to 2 m are also shown within the drainage ditches located behind the flood defences.

3.2.28 Figure 5 shows the inundation extents for the 0.5% AEP return period for the year 2010. The risk to people is flagged as ‘Caution’ (flood zone with shallow flowing water or deep still water). The outputs from the overtopping assessment suggest that part of the Paull part of the site is at risk during the 0.5% AEP event for the baseline scenario.

3.2.29 The overtopping assessment shows that the Hedon Haven North and Hedon Haven South parts of the site would not be affected by overtopping of the defences during a 0.5% AEP design event under the 2010 baseline.

Future Overtopping Assessment (2115)

3.2.30 Figure 6 shows that for the 0.5% AEP tidal flood overtopping scenario (2115) the majority of the Paull part of the site would be affected, with flood depths of up to 2 m across most of the site.

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In this scenario only a small raised area in the northern part of the site would remain free from inundation.

3.2.31 Both the Hedon Haven North and Hedon Haven south parts of the site would be affected by flooding under the 0.5% AEP plus climate change scenario, with depths of up to 2 m across the Hedon Haven South part of the site and up to 1m across the Hedon Haven North part of the site.

3.2.32 The risk to people was determined to range from ‘Dangerous for Most’ and ‘Dangerous for All’ across the Paull and Hedon Haven South parts of the site and up to ‘Dangerous to Some’ across the Hedon Haven North part of the site.

3.2.33 The overtopping scenario for the 0.1% AEP flood event plus climate change was not modelled in the study.

Risk from Overtopping

3.2.34 The western side of the Paull part of the site is considered to be at risk of inundation from floodwater overtopping the flood defences during the 0.5% AEP flood event on the Humber (baseline), with the entire site at risk during the 0.5% AEP event in the year 2115.

3.2.35 The Hedon Haven North and South parts of the site are not shown as being at risk from overtopping under 2010 baseline for the 0.5% AEP event, though significant flooding is shown on both sites under the future (2115) baseline for the same design event.

Breach Assessment

3.2.36 The information provided by the EA from the Humber North Bank defence breach assessments (EA, 2011a) included five breach assessments with locations from Paull Holme (2.5 km south- east of the Paul site site at National Grid Reference (NGR) 518990, 423990) to a breach at Lords Clough (1.4 km north-west of the Paull part of the site at NGR 515698, 428619).

3.2.37 The breach scenarios assume a 20 m or 50 m wide breach in the defence (depending on whether they are classed as hard or soft defences) on the rising part of the tidal cycle, with the breach down to ground level for a period of 72 hours (3 days). The assessment included simulating the 0.5% and 0.1% AEP events for baseline (2010) and for the year 2115 (including climate change). The breach assessments looked at the extent of flooding, depth and velocity of the floodwater and the hazard to people.

Baseline Breach Assessment (2010)

3.2.38 For the baseline 0.5% AEP event, a small area to the south of the Paull part of the site was shown as being affected by shallow flooding (<0.25 m) from a breach in the defences adjacent to the village of Paull (HB15), approximately 400 m to the south of the site. A hazard to people rating was determined with areas identified as ‘Dangerous for Some’ (i.e. children) with small isolated areas of ‘Dangerous for Most’, which corresponds with relatively deep and fast flowing water that is considered to be unsafe for the general public, though potentially not for the emergency services.

3.2.39 The entire Paull and Hedon Haven South parts of the site would be significantly affected by a breach at Paull Holme (HB14). A breach in this location would result in flood depths of up to 2 m at the site for the baseline 0.5% AEP tidal flood event. The model suggested a hazard to people rating of ‘Danger to Most’. Floodwaters from this breach location are modelled as

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reaching the two sites within 4 hours of the breach occurring. Figure 7 shows the maximum flood depths, velocity and hazard severity associated with the breach scenario at Paull Holme for this 0.5% AEP event (HB14).

3.2.40 The Hedon Haven North part of the site would be affected by a breach at Paull Holme, though the floodwater would be constrained to the southern half of the site, with depths being typically less than 0.25 m (as shown by Figure 7). However, a breach at the Salt End Chemical Works (HB16; Figure 8) indicates that the North part of the site would be affected by up to 2m of flooding for the 0.5% AEP event, with a corresponding hazard rating of ‘Danger to Most’. Under this scenario floodwaters could reach the site within 2 hours of a breach occurring.

Future Breach Assessment (2115)

3.2.41 The breach modelling shows that by the year 2115, all three of the sites would be inundated with floodwater from breaches at four of the five modelled locations for the 0.5% AEP tidal flood event. Figure 9 shows the results of a breach at Paull Holme under the 2115 baseline.

3.2.42 In all of the scenarios that the model suggested would affect the sites, floodwater is shown as inundating the majority of the area, with depths between 0.5 and 2 m and a hazard severity rating ranging between ‘Danger to Most’ and ‘Danger to All’.

3.2.43 In the worst-case 2115 0.5% AEP scenario, floodwaters may reach the Paull part of the site within 2 hours of a breach occurring at Paull (HB15). The modelling outputs show that floodwaters may reach the Hedon Haven South part of the site within 4 hours of a breach at Paull, whilst Hedon Haven North may be inundated within 2 hours of a breach occurring at Salt End (HB16).

Risk from Breach

3.2.44 The outputs from the breach assessment suggest that the majority of the three sites would be at risk from a breach in the defences. Floodwater is shown as inundating the Paull and Hedon Haven South parts of the site within 4 hours of the breach occurring at Paull Village under the 2010 0.5% AEP scenario. Hedon Haven North could also be inundated within 2 hours of a breach occurring at Salt End under the same design event.

3.2.45 Depths of flooding would typically be between 0.5 to 2 m for the 0.5% AEP 2010 scenario, with some localised areas being in excess of 2 m under the climate change (2115) scenario.

Tidal Flooding: Summary of Risk

3.2.46 All three sites lies predominantly within Flood Zone 3 (i.e. a high probability of flooding), although they are afforded protection by the presence of flood defences along Hedon Haven.

3.2.47 Though the conceptual flood defences heights are greater than the modelled 0.1% AEP still water levels (under the 2115 baseline), there is the residual risk of overtopping or breaching of the flood defences. The Paull part of the site is considered to be at the greatest risk from overtopping during the 0.5% AEP event under the 2010 baseline and all three sites are at risk from overtopping under the future 2115 climate chance scenario.

3.2.48 All three sites are at risk of a breach in the defences during a 0.5% AEP tidal flood event, with all three showing a potential time to inundation of approximately 2-4 hours under the worst- case breach location. Flood depth and hazard varies depending on the breach location, though

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modelled scenarios under the 0.5% AEP 2010 baseline typically depict flood depths between 0.5 m and 2 m, with localised depths in excess of 2m across all three sites.

3.2.49 Although the hazard to the sites in the event of a breach of the defences would be extremely high, it is a residual risk as the likelihood of a breach occurring is considered to be low; the EA regularly inspects the defences to ensure they are fit for purpose and this section of the flood defences is currently considered by the EA to be Grade 1 (i.e. ‘very good’) to Grade 2 (i.e. ‘good’).

3.2.50 It is noted, however, that the anticipated lifetime of the defences was estimated as being approximately 10-20 years from the time of the HFMRS assessment in 2008. Further, the EA have suggested that the lifetime of the defences on the south bank of Hedon Haven (adjacent to the Paull part of the site) may be less than previously assessed (5-10 years).

3.2.51 The residual risk to the sites will therefore increase after this timeframe unless the defences are maintained and/or improved in the near future.

3.2.52 The EA has stated it will attempt to secure defence improvements to the tidal defences currently securing the sites via the HFRMS, although contributions will be sought to ensure that Flood Defence Grant in Aid funding might be secured for this work.

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3.3 Fluvial Flooding

Local Watercourses

3.3.2 In addition to the flood risk posed by the River Humber, a number of watercourses cross the sites which pose a further fluvial flood risk. Local watercourses of relevance include:

• Preston New Drain; • Reedmere Sewer; • Burstwick Drain (which discharges into the Humber via Hedon Haven); and, • An unnamed ordinary watercourse within the Paull part of the site

3.3.3 Figure 3 shows the location of these watercourses.

3.3.4 The EA commissioned an assessment of the fluvial flood risk in this area as part of the NEECA2 South Holderness Study (EA 2011b). The EA’s South Holderness study outlines, reviews and summarises flood risk for South Holderness. The study analysed thirteen catchments within the South Holderness area, which includes catchments for Preston New Drain (which includes Reedmere Sewer) and Burstwick Drain. The study does not, however, take into consideration any flood defences present along the rivers and watercourses in the study area.

Preston New Drain and Reedmere Sewer

3.3.5 Preston New Drain is a small catchment of approximately 9 km2. The drain is culverted for 400 m out of 700 m through the Salt End Chemical Works, prior to discharging into Hedon Haven at Pollard’s Clough via a gravity outfall. It becomes tide-locked at high tides. Reedmere Sewer borders the northern extent of Hedon, flowing west towards the Salt End Chemical Works where it discharges into Preston New Drain.

3.3.6 The main flooding mechanism is through tide-locking combined with higher flows. This increases water levels within Preston New Drain, with overtopping of the banks and backing-up of field drains which are unable to discharge to the drain.

3.3.7 The agricultural land north of the A1033 was reported to have flooding during June 2007 (surface water and fluvial flooding). During the June 2007 event, water levels in Preston New Drain are reported to have been high but the Salt End Chemical Works were not flooded.

Burstwick Drain

3.3.8 The Burstwick Drain catchment drains an area of approximately 71 km2, is classified as a main river from to the Humber Estuary and drains into the River Humber via pointing doors at Hedon Haven.

3.3.9 The tidal barrier was constructed in 1969 and was designed so that it could be converted into a pumping station if required. Burstwick Drain becomes tide-locked at high tides. This influences fluvial flooding, but also surface water flooding where surface water drainage is unable to discharge into Burstwick Drain.

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3.3.10 The EA has confirmed that the tidal outfall utilises hinged wooden pointing doors that open and close with the tides. There are vertical gates upstream of the pointing doors, that can be closed to prevent the incursion of the tide should the pointing doors fail. In addition, the EA deploys a 24-inch mobile pump to pump over flows from Burstwick Drain into the downstream tidal section whilst the outfall is tide-locked. The EA state that these measures, deployed a number of times a year, alleviate the risk of flooding to Burstwick and Hedon settlements.

3.3.11 The EA has confirmed that dredging and channel modifications have been undertaken on the watercourse in an attempt to increase the carrying capacity. It was reported to reduce the flooding hazard, but not significantly (Yorkshire Post, 2012).

Unnamed Ordinary Watercourse (Paull part of the site)

3.3.12 An unnamed ordinary watercourse crosses the Paull part of the site and flows from south to north prior to discharging into Hedon Haven via a flapped gravity outfall, as shown by photograph 6, Appendix A.

3.3.13 South West Holderness Councillors have stated that the catchment for the watercourse includes Paull Village and that it plays a key role in collating and removing surface water from the settlement and the surrounding land.

Historic Fluvial Flooding

3.3.14 The EA South Holderness Study (2011) identifies that the South Holderness area was affected by both fluvial and surface water flooding during the large scale flooding experienced across the UK during the summer of 2007.

3.3.15 Figure 4 shows the extent of flooding on the site in June 2007. Due to extremely heavy and prolonged rainfall on the 14th and 15th of June, ground in the East Riding area became saturated. Subsequently intense rainfall between the 23rd and 25th of June caused surface water to overwhelm the existing drainage system in Hedon, which discharges into Burstwick Drain. River and drain levels rose rapidly and in some cases overtopped the defences (EA, 2010). The EA has provided data which suggests that flooding occurred on the three sites. This could possibly be a consequence of the capacity of the land drains and watercourses being exceeded, runoff from roads or saturation of the underlying ground.

3.3.16 Fluvial flood defences have been raised upstream in Hedon following the June 2007 surface water and fluvial flooding (EA, 2010a). However, there are no formally recognised defences along Burstwick Drain between the tidal barrier and the . Steep channel banks indicate some capacity for floodwater, although the banks are not elevated above ground level.

Modelling of Fluvial Flood Risk

3.3.17 The EA’s South Holderness study incorporates the results from strategic 2D fluvial modelling undertaken in the Hull and Coastal Streams Catchment Flood Management Plan (CFMP).

3.3.18 The Hull and Coastal Streams CFMP consultation report was published in May 2010. The CFMP is a high-level planning tool that sets an overall framework for managing flood risk at a catchment scale. The Hull and Coastal Streams CFMP is divided into several policy units, three of which are included within the South Holderness Study area.

3.3.19 As part of the CFMP process, broad-scale modelling was undertaken to improve the understanding of fluvial flood risk at the catchment scale. The flood flow was obtained for

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various flood probabilities at every 200 m of watercourse where the catchment is greater than 3 km2. These flows were obtained from the National Inflows Database, and are based on FEH methods. The channel capacity was either estimated or predetermined through existing knowledge, and the flow in excess of this capacity was routed over a DEM surface of the floodplain.

3.3.20 The South Holderness study specifically reviews the modelled results from the CFMP for both the 1% AEP and the 0.1% AEP undefended fluvial flood outlines.

3.3.21 The mapping shows that the large majority of the Hedon Haven North part of the site is within the 1% AEP undefended fluvial flood outline (as associated with Reedmere Sewer, Preston New Drain and Burstwick Drain). A marginally greater area of this site is therefore within the 0.1% AEP undefended outline.

3.3.22 The southern sites are shown to be less affected by fluvial flooding. In terms of the Paull part of the site, the 1% AEP undefended fluvial flood extent is confined to a small area of the site’s north-east corner and the 0.1% AEP outline extends further into the site, covering approximately 20% of the land.

3.3.23 Hedon Haven South is shown as being at risk of flooding from the 1% AEP undefended fluvial flood in its north-west corner, with the extent running between Burstwick Drain and Paull Road. In this instance the 0.1% AEP undefended fluvial outline is not significantly greater than that associated with the 1% AEP undefended outline.

Fluvial Flooding: Summary of Risk

3.3.24 The data collated from the EA South Holderness study, the EA and the Hull and Coastal Streams CFMP indicates that the three sites are in an area considered to be at a high risk of fluvial flooding.

3.3.25 In general, the South Holderness study identifies that fluvial flood risk in this area arises from a combination of factors, including:

• the low lying nature of this area means that many of the drainage channels have a low gradient, and therefore flood water is not conveyed as quickly through the catchment and the tidal outfall creeks to the Humber Estuary; • many of the drainage channels (including Preston New Drain, Reedmere Sewer and Burstwick Drain) within the South Holderness area have a gravity outfall to the River Humber. At high-tides the drainage channels become tide-locked, as they are unable to discharge into the River Humber; • the combination of low gradients and tide-locking makes these watercourses prone to flooding when a high-tide coincides with a high rainfall event; and • the lack of gradient and tide-locking also encourages siltation of the watercourses, further reducing channel capacity and gradient.

3.3.26 The broad-scale modelling is the only information received from the Environment Agency on fluvial flood risk. Due to the broad-scale nature of the assessment, the outputs should be treated with caution when considering them in relation to a site-specific assessment.

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3.4 Groundwater Flooding

3.4.1 A large proportion of the East Riding area is underlain by Chalk, a Principal Aquifer that is highly susceptible to rising groundwater levels following heavy rainfall. The Level 1 SFRA notes that groundwater flooding has been documented in several locales in the wider area but there have not been any incidents reported around Paull and Hedon.

3.4.2 The superficial geology on the sites is largely composed of impermeable estuarine clays that prevent the upward movement of groundwater (EA, 2012c); this is reflected in the groundwater emergence map commissioned by Defra in 2004.

3.4.3 The groundwater emergence map shows two small areas of potential emergence in the Hedon Haven South part of the site; these areas correspond with superficial glacial sand and gravel deposits that are classified as a Secondary A Aquifer.

3.4.4 The EA’s South Holderness study corroborates the conclusions of the Level 1 SFRA, stating that there is very limited potential for groundwater flooding from the Chalk aquifer due to the capping effect of the thick boulder clay. Little recharge to the Chalk is therefore likely to occur in the South Holderness area. In the confined aquifer, fluctuations due to recharge are less marked (response lags by several months) and, where present, pumping effects dominate.

3.4.5 A British Geological Survey borehole TA12NE192a was drilled off-site where the A1033 borders the Salt End industrial complex, in 1992. Borehole logs indicate that a groundwater strike was found at 10.80 m below ground level (bgl) which represents groundwater may be present in or perched upon the low permeability clays. Groundwater is likely found within the low permeability clays of the alluvium and Glacial Till. However, this is likely to be discontinuous and influenced by sand and gravel lenses within the clay where present. Given the site’s proximity to the Humber Estuary, the groundwater level may possibly be tidally influenced.

3.4.6 Elevations within the sites vary, though they sit predominantly between 2 – 4 mAOD. Based upon the above information, the risk of groundwater flooding is therefore considered to be low.

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3.5 Surface Water Flooding

Local Context

3.5.2 The Level 1 SFRA identifies that the risk of surface water flooding is an important consideration in East Riding; approximately 6,000 homes, 200 businesses, 38 schools and 12,000 ha of agricultural land were affected in East Riding during the summer 2007 event, and surface water flooding was the primary source of flooding in this instance (Jacobs, 2010).

3.5.3 The EA South Holderness study states that the area is particularly susceptible to surface water flood risk due to the flat topography. Ponding of surface water affected flooding of agricultural land during June 2007, and surface water runoff contributed to flooding of properties and roads within key settlements, including the town of Hedon to the north-east.

3.5.4 Figure 4 shows the documented extent of surface water flooding on the site in June 2007. Due to extremely heavy and prolonged rainfall on the 14th and 15th of June, ground in the East Riding area became saturated. Subsequently intense rainfall between the 23rd and 25th of June caused surface water to overwhelm the existing drainage system in Hedon, which discharges into Burstwick Drain. River and drain levels rose rapidly and in some cases overtopped the defences (EA, 2010a).

3.5.5 High water levels within drainage channels and ditches exacerbated this problem by preventing surface water drainage systems discharging into them via gravity outfalls, causing backing-up of these systems. Under such conditions gravity-driven surface water drains may become unable to discharge into the Burstwick Drain (pers comm. East Riding of Yorkshire Council).

3.5.6 The surface water drains discharging into Burstwick Drain have been known to be locked for days at a time and the EA indicated that 70% of property flooding in Hedon and Burstwick was caused by surface water flooding in 2007 (pers comm. East Riding of Yorkshire Council).

3.5.7 The severity of the surface water issues in the area prompted East Riding of Yorkshire Council to commission a review of existing evidence of flood risk in Hedon. The review considered potential mitigation options, including a pumping scheme estimated to cost in the region of £7.3 million. East Riding of Yorkshire Council has advised that although several options have been explored, the construction of a detailed hydraulic model for option testing is recommended prior to implementing further mitigation.

3.5.8 The review advises that the most appropriate flood risk management strategy for Hedon would include a mixture of some strategic solutions (such as a Burstwick Drain diversion channel to the Humber), and some site specific measures to mitigate against the risk of surface water flooding.

SFRA Pluvial Modelling

3.5.9 To assist with identifying the potential severity of the surface water hazard, the Level 1 SFRA undertook strategic level pluvial modelling to identify where localised flooding could occur as based upon depressions in topography (i.e. where ponding can occur) and geology (i.e. where soils are highly impermeable and can reduce infiltration into the ground during wet weather). Figure 11 shows the indicative severity of the surface flood hazard across the sites.

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3.5.10 As Figure 11 shows, there are several small depressions across the site showing a low surface water hazard severity (equivalent to depressions in the topography of between 0.2 – 0.5 m). These modelled hazard areas also reflect upon the impermeable tidal clays that underlie the site and the location of the drainage ditches, particularly Reedmere Sewer and the drain on the Paull part of the site that outfalls into Hedon Haven. The site is considered to be at low risk from off-site sources of surface water flooding.

Existing Surface Water Runoff Rates

3.5.11 As new developments should not increase the risk of flooding to their site and elsewhere, it is necessary to calculate the existing rates of surface water runoff to form a basis for comparison with the rates from future development.

3.5.12 As the site is entirely greenfield, the IoH124 method for calculating runoff from small catchments was utilised in the WinDes micro drainage software. The results of this calculation are shown for a range of return periods, including climate change in Table 2 below.

Table 2: Existing surface water runoff rates

Return period Runoff (years) (l/s per hectare)

QBAR (mean annual) 2.8

30 4.2

100 5.0

100 + CC 6.5

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3.6 Limitations or Difficulties

3.6.1 The main limitations associated with the flood risk baseline assessment relate to data gaps and with the quality of data provided.

3.6.2 The risk of a combination of how tide-locking may interact with high fluvial flows is unknown.

3.6.3 The extent to which the tides influence the surface water drainage on the site is relatively uncertain. Whilst it is understood that tide-locking of Burstwick Drain can result in the local surface water gravity drains becoming impeded, it has not been possible to quantify how this may affect the surface water drainage on the HAV1/2 site. Tide-locking occurs twice daily at Hedon New Clough on the end of Burstwick Drain. However anecdotal evidence indicates that locking of Hedon's surface water drains draining via gravity can occur for days at a time during severe weather due to prolonged high-water levels in the drain.

3.6.4 It is not known how tide-locking affects drains that outfall on the Humber side of the tidal barrier and whether tidal backflow up these drains is possible.

3.6.5 The BGS borehole log from Salt End that was used to infer the groundwater conditions was produced in 1992. It was also not taken directly onsite, but within the Salt End industrial area on the A1033. Though other evidence suggests the risk of groundwater emergence is low, it is important to acknowledge that groundwater levels may now be different to that reported by the BGS log.

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4 Future Considerations for Development

4.1.1 This section provides information on the types of flood risk mitigation measures that may need to be considered when developing the site.

Fluvial and Tidal Flooding

4.1.2 The HFRMS states that the flood defences were anticipated to have a remaining life of 10 to 20 years from when the document was written in 2008, and that a visual inspection undertaken on behalf of the EA in 2011 suggested that the lifetime of the defences on the south bank of Hedon Haven may be less than previously assessed (5-10 years). The defences will therefore need to be improved as sea levels rise and the existing defences deteriorate.

4.1.3 The EA have stated they will attempt to secure defence improvements to the tidal defences currently securing the sites via the HFRMS, though they will need contributions to ensure that they can secure Flood Defence Grant in Aid funding for this work.

Management Options

4.1.4 Due to the residual risk associated with a breach or overtopping of the flood defences, it is recommended that an emergency plan be prepared for any developments (both for construction and operation phases), in liaison with ERYC. All personnel entering the sites should be inducted and aware of all the appropriate health and safety procedures related to the plan.

4.1.5 All developments should adopt the emergency plan, which would provide appropriate action levels and procedures in case of a flood warning and breach of the defences. For example, the emergency plan could include:

• commitment that all developments sign up to the EA’s Floodline flood warning and notification system – this will inform the critical point at which the ground floor and outdoor areas should be evacuated and the procedures for monitoring or receiving notice of this critical point; • procedures for safe evacuation of the ground floor and outdoor areas; • details of appropriate access and egress routes; • details of appropriate safe passages to safe upper levels (refuges), including how safe routes will be marked within the building, such as appropriate signage; and • details of responsibilities for the implementation of the emergency plan and for ensuring it remains up to date and that site staff are aware of the procedures.

4.1.6 Although the sites do not lie within an existing Flood Warning Area (FWA), it is adjacent to the North Bank of the Humber Estuary at Paull and Paull Holme Sands FWA. It also resides within the larger geographic area of the Humber Estuary from Pumping station to Lords Clough, for which the EA provides a general Flood Alert notification in instances of possible flooding. Subscription to the EA Flood Alert notifications would enable personnel working on the sites to receive flood warnings when the Humber Estuary levels are high.

4.1.7 Appropriate evacuation routes (and associated access and egress) would be dependent on the location of a breach in the defences; the outputs from the EA’s breach modelling suggest that

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floodwater may inundate access roads to the north or to the south of the site depending on the location of the initial breach. The evacuation plan should therefore need to consider multiple routes of access and egress.

4.1.8 Provision of an internal safe refuge should be provided and an appropriate emergency evacuation/ invacuation plan created. Since the sites are in close proximity to the Humber Estuary, safe refuge may be necessary because there may be relatively little lead time from the flood warning following a breach of the defences and the site being inundated (if the breach is close to the site).

4.1.9 Safe refuge could be a communal space in the building that can be accessed via internal stairs and is above the maximum modelled flood depth resulting from a breach in the defences during a 0.5% AEP event (which varies between 0.5 - 2.0 m, as shown in Figure 7). Areas of safe refuge should not constitute ‘dry islands’ and essential supplies such as food, water and medical treatment should be available within the safe refuge for the duration of the flood event.

4.1.10 Opportunities could be taken to adopt flood resilient design techniques on the ground floor, and to allow for the removal of water in the event of inundation. The utilisation of flood resilient construction techniques would assist with managing the residual risk associated with a breach in the flood defences and from fluvial flooding associated with Burstwick Drain, Reedmere Sewer, the ordinary watercourse and land drains. Resilient construction measures would reduce the impact of a flood event on the structure of the building and enable quicker recovery following a flood.

4.1.11 Extremely sensitive equipment (such as electricity sub-stations, machinery) could be located above the flood level or contained in areas that are resistant to floodwater (i.e. areas incorporating an exclusion strategy).

4.1.12 There will be a residual risk of flooding associated with fluvial and tidal sources, including Burstwick Drain, ordinary watercourse and land drains. Consideration should be given to this when determining the site layout, by sequentially locating uses considered more vulnerable to flooding away from high risk areas.

Surface Water Management

4.1.13 Surface water generated as a consequence of development on the site will need to be managed so that it does not increase the risk elsewhere.

Paull (HAV1)

4.1.14 The EA has confirmed (EA, 2012a) that surface water from the Paull part of the site could be discharged into the Humber Estuary at a potentially unrestricted rate. This is considered to be acceptable in relation to flood risk considerations, due to the large tidal regime of the Lower Humber. Unrestricted discharge from the site would not increase the risk of flooding from the Humber Estuary elsewhere, because the volume of water entering the Humber would be negligible relative to the extremely large volumes of water associated with the tidal cycle.

4.1.15 Although it may be acceptable to discharge at an unrestricted rate into the Humber Estuary, a pumping system would likely be required due to the tide-locking of gravity based outfalls during high tide. Tidal predictions for King’s Dock in Hull shows that the water level regularly exceeds 6.9 m Above Chart Datum (ACD), which corresponds with the an elevation of 3 m AOD. The topographic elevations behind the flood defences on the Paull part of the site are below

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3 m AOD. Surface water would therefore be unable to continually drain into the Humber Estuary via gravity. The surface water drainage system may discharge via gravity at low tides, though a pumping facility would ultimately be required to ensure the effective drainage of the site under all tidal conditions.

4.1.16 Should a pumping facility be considered to be unfeasible (due to cost or other reasons), it is recommended that the development provide a sufficient volume of surface water storage to restrict discharge into the existing tidal outfall to a greenfield runoff rate for the 1% AEP rainfall event plus climate change (+20%).

4.1.17 A storage facility, such as a balancing pond or attenuation lagoon, could therefore enable surface water flows to accumulate and be stored when the gravity-based outfalls are tide- locked, thereby meeting with the requirements of the SFRA with regards to temporary exceedance of the drainage system.

4.1.18 The Paull LDO Flood Risk Assessment (URS, 2013) was produced in support of an application for industrial use on the Paull (HAV1) site. The report presents a high-level level assessment of the worst-case attenuation volumes that may be required to retain surface water on-site during tide-locking of an outfall.

4.1.19 The calculations presented within the report assume that:

• the site layout, uses and proportion of the site to be covered by impermeable surfaces are unknown. The high-level assessment assumes that 80% of the site is impermeable (equivalent to approximately 64 hectares). This was considered to be a conservative assumption; • it was assumed that there will be a restricted discharge at a greenfield rate of 1.4 litres/second/hectare into the ordinary watercourse which passes through the site and discharges into Hedon Haven; • calculations have been undertaken to determine storage volumes for the 1% AEP design storm event plus a 30% allowance for climate change; • due to the size of the site, WinDes outputs suggest a critical storm duration of 48 hours. In reality, there could be an opportunity to discharge at a higher than greenfield rate whilst the water levels in the Humber Estuary and Hedon Haven are lower during the tidal cycle; and • no infiltration within the storage volume has been allowed for, thereby giving a conservative estimate in lieu of detailed percolation testing and confirmation of the ground conditions.

4.1.20 The indicative calculations undertaken within the FRA suggest that the storage requirements for the LDO site in aggregate would be in the region of 57,000 - 70,000 m3. The area of land required to accommodate the storage volume is dependent on the depth of water storage. Table 3 below provides an indication of the indicative storage per hectare of the site, total area requirements and what this is as a proportion of the total site area.

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Table 3: Indicative attenuation storage volumes for the Paull part of the site (i.e. HAV1) (80% impermeable)

Indicative Storage 2 Land Take (hectares) Proportion of Site (%) (m /hectare)

Storage Depth (m) Min Max Min Max Min Max

1.0 716 879 5.7 7.0 7.2 8.8

1.5 477 586 3.8 4.7 4.8 5.9

2.0 358 440 2.9 3.5 3.6 4.4

4.1.21 Based on these indicative volumes, potential area requirements (assumed to constitute an 80% impermeable area), it is confirmed that the Paull part of the site can accommodate the storage requirements based on a greenfield discharge rate of 1.4 l/s/ha.

4.1.22 As the site layout becomes defined, detailed assessments can be undertaken to determine the extent that the critical storm, the impact of water levels in the Humber Estuary and/or Hedon Haven, and the potential solutions available have on these numbers. This can then be used to determine the optimum storage volumes.

4.1.23 As previously highlighted, alternative means of discharging surface water may also be established through the detailed design stage, and may include options such as pumping surface water into the Humber Estuary or Hedon Haven during high-tides. Using a pumped system would reduce the volume of storage that would be required on site because the discharge rate could be substantially higher than a greenfield rate (for example, a continual pumped rate of 300 l/s could reduce the volume of storage to in the region of 42,000 m3 - 59,000 m3). However any such method would need to be subject to its own application.

Hedon North and Hedon South (HAV2)

4.1.24 Surface water runoff from the Hedon Haven North and South parts of the site would have to be carefully managed as they are not directly adjacent to the Humber Estuary and may have to discharge into one of the local watercourses (i.e. Reedmere Sewer or Burstwick Drain). Due to the issues of tide-locking, channel capacity and history of flooding around Hedon, any discharge into these watercourses would have to be restricted to the equivalent greenfield runoff rate in order to avoid increasing flood risk elsewhere. Pumping may be also be required to overcome the difference in site-levels and the water level within the watercourses during tide-locking.

4.1.25 In order to determine the likely attenuation volumes that would be required to restrict discharge from both Hedon North and South (i.e. HAV2) to a greenfield runoff rate, the WinDes quick storage estimate has been utilised in line with the methodology utilised by the 2013 Paull LDO FRA. In brief, the WinDes calculations assume that:

• the site layout, uses and proportion of the site to be covered by impermeable surfaces are unknown. Unlike the calculations presented in the Paul LDO FRA (which was undertaken specifically for a large industrial complex), this assessment assumes that approximately

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60% of the combined Hedon North and South area (i.e. HAV2) is impermeable, which is equivalent to approximately 92 hectares; • it is assumed that there will be a restricted discharge at a greenfield rate (1.4 litres/second/hectare); • calculations have been undertaken to determine storage volumes for the 1% AEP design storm event plus a 30% allowance for climate change; and • no infiltration within the storage volume has been allowed for, thereby giving a conservative estimate in lieu of detailed percolation testing and confirmation of the ground conditions.

4.1.26 Table 4 presents the results of the above calculation.

Table 4: Indicative attenuation storage volumes for Hedon North and South (i.e. HAV2) (60% impermeable) Indicative Storage Requirement Land Take (hectares) Proportion of Site (%) (m2/hectare)

Storage Depth (m) Min Max Min Max Min Max

1.0 539 665 8.3 10.2 10.4 12.8

1.5 360 444 5.5 6.8 6.9 8.5

2.0 270 333 4.1 5.1 5.2 6.4

4.1.27 Based on the above indicative volumes and potential area requirements it is confirmed that the combined Hedon North/ South parts of the site (together comprising the HAV2 allocation) can feasibly accommodate the storage requirements as based upon a greenfield discharge rate of 1.4 l/s/ha.

4.1.28 Dependent on the detailed design of the overall surface water drainage system, it may be possible to direct runoff from the Hedon Haven South part of the site through the Paull part of the site and into the Humber Estuary. This could potentially reduce the total volume of attenuation storage required on site should the drainage system be permitted to discharge into the Humber Estuary at rates above the standard greenfield stipulation.

Other Surface Water Considerations

4.1.29 The SFRA states that sustainable drainage systems (SuDS) must be implemented on all sites, unless it can be demonstrated that they are not practicable or that they will present an unacceptable pollution risk to controlled waters. Any SuDS design must take into account the presence of groundwater (for example, a high water table) and underlying geological conditions. The site is not located in a groundwater source protection zone, so infiltration based SuDS may be appropriate. However, borehole information for locations close to the site shows that there are clays present. This suggests that infiltration type SuDS might not be appropriate for the development, though this will need to be confirmed by undertaking infiltration tests. If infiltration based SuDS are not appropriate for the site then focus will need to be on retention on site, for example, rainwater harvesting, green roofs, permeable surfaces, swales, ponds and wetlands can all operate without infiltration

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4.1.30 Since the sites are situated around an existing network of drainage ditches, it may be necessary to divert and/ or culvert them. However, the ordinary watercourse that passes through the Paull part of the site is currently envisaged to remain open, with a 9 m easement either side of the banks for maintenance and access (ERYC, 2012).

4.1.31 Based upon observations made during a site visit and a review of Ordnance Survey mapping, land drains to the south and east of the Paull part of the site are understood to discharge into the land drains and ordinary watercourse that traverse the Paull part of the site. It will therefore be necessary to ensure that after any diversions to the drainage ditches on-site, the off-site land drains either retain their connection with the ordinary watercourse and the drainage network, or are diverted away from the site with new outfalls constructed to the Humber Estuary.

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5 Conclusions

5.1.1 Using all available information, the flood risk to the sites from all sources has been identified. In summary:

• the main source of flooding to the site is from the tidal Humber. The majority of the site lies within Flood Zone 3 and therefore the default risk of tidal flooding is high (>0.5% AEP ). According to the flood zone maps, the EA does not classify the area as benefiting from defences, however conceptual defence levels and a topographic survey indicate the embankments along the Paull part of the site are above the modelled still water levels for the 0.5% AEP event . The risk of tidal flooding can therefore be considered to be less than the indicative flood zone map otherwise indicates. At present, the EA considers all of the defences in the area to be in good to fair condition; • the Humber Flood Risk Management Strategy (HFRMS) indicates that the flood defences around Hull are assigned a standard of protection of up to the 0.5% Annual Exceedance Probability (AEP) tidal flood event, though the defences around Paull only afford protection up to the 1% AEP tidal flood. The HFRMS states that the defences may only have a lifetime of 10-20 years from the time of their assessment in 2008. Correspondence with the Environment Agency suggests that the lifetime of the defences along the south bank of Hedon Haven is in the region of 5-10 years; • although the flood defences are currently above the height of the modelled water levels for the 0.5% AEP event plus climate change, work undertaken in the Humber North Bank modelling study (EA, 2011a) shows that areas along the western site boundary of the Paull part of the site are at risk of flooding due to wave-induced overtopping for the 0.5% AEP event in 2010. The area and severity of the overtopping is projected to increase due to the effects of climate change, with modelling suggesting flood depths of up to 2 m across the majority of the Paull and the Hedon Haven South parts of the site and up to 1 m of flooding for the Hedon Haven North part of the site by 2115. Whilst the lifetime of the developments may not extend to 2115, it is anticipated that the risk of flooding from overtopping will increase during the lifetime of the development; • there is also the residual risk of a breach in the flood defences. Though the likelihood of this occurring is very low due to the regular maintenance and inspection of the defences, breach modelling simulations centred at Paull Holme show potential flood depths of up to 2 m across the sites for the 0.5% AEP tidal flood event. The simulation outputs for flood hazards to people show that floodwaters would be predominantly considered to be ‘Danger to Most’, with a time to inundation of approximately 4 hours under the current baseline. In a similar manner to the risk of overtopping, the severity of flooding resulting from a breach is anticipated to increase due to the effects of climate change; • the large majority of the sites are also shown to be at risk of flooding from the 1% AEP fluvial event associated with the local watercourses and drainage. The flood mapping does not, however, account for the presence of any fluvial flood defences; • the risk of surface water flooding is considered to be high. EA mapping indicates that areas of the site were flooded in June 2007. Surface water modelling undertaken for the SFRA identifies that some of the site may be susceptible to flooding. Impermeable estuarine clays also underlie the site and will likely inhibit infiltration of rainfall, potentially resulting in ponding of surface water on the surface. Furthermore, the surface water drains on the site

Hedon Haven Baseline Study September 2013 Flood Risk 24 East Riding of Yorkshire Council Hedon Haven Evidence Base

outfall into Hedon Haven and Burstwick Drain and may become tide-locked and unable to discharge during high water levels in the receiving waterbodies; and • the risk of groundwater flooding to the site is considered to be low. BGS Borehole data near the site indicates groundwater was found to occur at 10.8 m bgl. Groundwater emergence maps do not indicate that the site is at risk and the impermeable estuarine clays that underlie the site will likely prevent groundwater from emerging at the surface.

Implications for Development • The Technical Guidance to the National Planning Policy Framework stipulates that ‘Less Vulnerable’ and ‘Water Compatible’ types of development are considered appropriate within Flood Zone 3. Less Vulnerable development includes offices, general industry, storage and distribution and non-residential institutions. • As the site is almost wholly within Flood Zone 3, future development can only be considered follow the application of the Sequential Test whereby new development is steered towards areas with the lowest probability of flooding. The Flood Zones therefore form the starting point for this sequential approach and development in Flood Zone 3 would only be considered where there are no reasonably available sites in Flood Zones 1 and 2. The Exception test would be required if the proposed development incorporates ‘More Vulnerable’ development (e.g. residential) and ‘Essential Infrastructure’ (e.g. power stations) within Flood Zone 3. • The SFRA states that a flood risk assessment would be required to show how the building and its users will be made safe in the event of a flood event. Safe refuge should be made available on the upper floors, providing an immediate route of escape should a breach occur in the flood defences. It is unlikely that basements would be permitted as they are subject to rapid inundation without warning in the event of a breach of the flood defences. • New development would have to provide an 8 m easement along the watercourses and flood defences. For Reedmere Sewer this is increased to 9 m due to local byelaws. The EA and LPA are likely to encourage that the number of crossings of watercourses and drains are kept to a minimum, to reduce the extent of culverting. The culverting of watercourses would need to consider the potential impact upstream. • Surface water management strategies that discharge into Reedmere Sewer or Burstwick Drain will need to restrict discharge from the site to the equivalent Greenfield runoff rate. This will require the provision of surface water storage to ensure that the flood risk to the site and surrounding area is not increased. Indicative attenuation storage volumes to accommodate the 1% AEP design storm event plus an allowance for climate change, have been calculated for the Hedon Haven North and South parts of the site based on a range of impermeable areas. The calculations suggest that significant storage will be required if discharge is restricted to a Greenfield runoff rate. • Pumping of surface water into Reedmere Sewer or Burstwick Drain may be required due to tide-locking. If pumping is necessary then level control will be required to ensure that no pumping occurs when the levels in the receiving watercourse reach an agreed maximum level. The Maximum cut-off level for any pumping will be agreed with the EA and the South Holderness IDB. A surface water drainage strategy should therefore take into account the requirement for the provision of attenuation storage during periods when the cut-off level is exceeded.

Hedon Haven Baseline Study September 2013 Flood Risk 25 East Riding of Yorkshire Council Hedon Haven Evidence Base

• Since the Paull part of the site borders the Humber Estuary, it could be acceptable to discharge surface water into the Humber Estuary at an unrestricted rate. However, the discharge of surface water into the Humber Estuary will need to consider the impact of tide- locking. It is anticipated that pumping will be required to ensure surface water can be discharged during high tides. Storage of surface water may still be required on site to attenuate the 1% AEP design storm event plus climate change and the volume of storage required on site will depend on the discharge/ pumping rate at the outfall. • The SFRA states that SuDS must be implemented on all sites, unless it can be demonstrated that they are not practicable or that they will present an unacceptable pollution risk to controlled waters. Any SuDS design must take due account of groundwater and geological conditions. Borehole information for locations close to the site shows that there are clays present, which suggests that infiltration type SuDS might not be appropriate for the development. However, this cannot be confirmed until infiltration tests are undertaken.

Hedon Haven Baseline Study September 2013 Flood Risk 26 East Riding of Yorkshire Council Hedon Haven Evidence Base

6 References

Department for Communities and Local Government (2012) National Planning Policy Framework

Department for Communities and Local Government (2012) Technical Guidance to the National Planning Policy Framework

Department for Food and Rural Affairs (20076) FCDPAG3 economic Appraisal Supplementary Note to Operating Authorities – Climate Change Impacts

East Riding of Yorkshire Council (2011a) Preliminary Flood Risk Assessment

East Riding of Yorkshire Council (2011b) Infrastructure Study 2013

Environment Agency (2008) The Humber Flood Risk Management Strategy

Environment Agency (2010a) Burstwick and Hedon Flood Report

Environment Agency (2011a) River Humber, North Bank Tidal Modelling Report

Environment Agency (2011b) NEECA2 South Holderness Study, Assessment of Flood Risk, 211366-00, March 2011

Environment Agency (2012a) Personal Communication

Environment Agency (2012b) Response to Draft Additional Analysis of Flood Risk in Hedon Paper

Environment Agency (2012c) Data request correspondence

Jacobs (2010) East Riding Strategic Flood Risk Assessment

Law, FM, Black, AR, Scarrott, RMJ, Miller JB and Bayliss, AC (2012) Chronology of British Hydrological Events. Access online on 12/7/2012 at: http://www.trp.dundee.ac.uk/cbhe/welcome.htm

Marshall, D.C.W. & Bayliss, A.C. (1994) Flood estimation for small catchments. Report No 124

Murphy, J.M., Sexton, D.M.H., Jenkins, G.J., Boorman, P.M., Booth, B.B.B., Brown, C.C., Clark, R.T., Collins, M., Harris, G.R., Kendon, E.J., Betts, R.A., Brown, S.J., Howard, T. P., Humphrey, K. A., McCarthy, M. P., McDonald, R. E., Stephens, A., Wallace, C., Warren, R., Wilby, R., Wood, R. A. (2009) UK Climate Projections Science Report: Climate change projections. Met Office Hadley Centre, Exeter.

National Meteorology Library and Archive (2011) Saturday 31 January 1953: East Coast Floods

Yorkshire Post (2012) Flooding study confirms limited impact of drain maintenance. Accessed online on 12/7/2012 at: http://www.yorkshirepost.co.uk/news/around-yorkshire/local- stories/flooding study confirms limited impact of drain maintenance 1 3456095

URS (2013) Paull LDO Flood Risk Assessment

Hedon Haven Baseline Study September 2013 Flood Risk 27 East Riding of Yorkshire Council Hedon Haven Evidence Base

FIGURES

Hedon Haven Baseline Study September 2013 Flood Risk 1 Key Hedon Haven North site

Hedon Haven South site

Paull site

Site Location

Copyright Reproduced from Ordnance Survey digital map data (c) Crown copyright 2012. All rights reserved. Licence number 0100031673

Drawing Title Scale @ A4 1:100,000 & NTS FIGURE 1 Drawn Checked Approved CLH LM LM Date Rev SITE LOCATION PLAN 25.09.13 www.ursglobal.com HEDON HAVEN Drawing Number N

Hedon Haven North site

Key

Site boundaries

Outfall Hedon Haven South site Main river

Flood defences Paull site June 2007 February 1953

Areas benefiting from flood defences Flood Zone 3 Flood Zone 2

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 2 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street ENVIRONMENT AGENCY CLH CLH RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client INDICATIVE FLOOD ZONE MAP 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

NHUM_055 OT56 Main River (unnamed) Reedmere Sewer

NHUM_056

NHUM_054

OT54 Hedon Haven North site

Burstwick Drain 1232102410201L01001 1232102410201L01006 1232102410201L01005 1232102410201L01004

NHUM_057 1232102410101L03001

NHUM_051

Tidal Barrier

OT52 OT50 Key Hedon NHUM_052 Haven Site boundaries

NHUM_050 Outfall Hedon Haven South site Modelled water level nodes NHUM_053 Conceptual Flood defence sections Paull site Watercourse

1232282760501L06001

NHUM_049

OT49

OT48

NHUM_048

OT48

NHUM_047

OT46 NHUM_046

1232282760501L05001

1232282760501L04003 NHUM_045

1232282760501L04002

OT45 1232282760501L04001

OT44

Copyright Environment Agency copyright and / or database rights 2011. All rights NHUM_044 reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 3 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street WATER COURSE AND CLH CLH RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client FLOOD DEFENCE MAP 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Hedon Haven North site

Hedon Haven South site

Paull site

Key

Site Boundary

2007 Historic Flood Outline

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 4 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street 2007 HISTORIC FLOOD OUTLINE CLH CLH RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Key Site Boundary

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 5 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street OVERTOPPING SCENARIO-0.5% AEP (2010) PB PB RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Key Site Boundary

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 6 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street OVERTOPPING SCENARIO-0.5% AEP (2115) PB PB RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Key Site Boundary

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 7 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street BREACH SCENARIO AT PAULL HOLME PB PB RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client (0.5% AEP (2010) 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Key Site Boundary

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 8 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street BREACH SCENARIO AT SALT END PB PB RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client (0.5% AEP (2010) 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Key Site Boundary

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 9 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street BREACH SCENARIO AT PAULL HOLME PB PB RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client (0.5% AEP (2115) 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Key

Site Boundary

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 10 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street FLUVIAL FLOOD MAPPING PB PB RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS N

Key

Site Boundary

Copyright Environment Agency copyright and / or database rights 2011. All rights reserved. (c) Crown Copyright and database right. All rights reserved. Environment Agency, 100026380, 2012

Project Title Drawing Title Purpose of issue FINAL URS Infrastructure & Environment UK Limited FIGURE 11 Designed Drawn Checked Approved Date WESTONE HEDON HAVEN Wellington Street INDICATIVE SURFACE WATER PB PB RJ RJ 29.09.13 URS Internal Project No. Suitability Leeds, LS1 1BA Tel: (0113) 204 5000 Client FLOOD HAZARD 47062982 Drawing Number Rev Fax: (0113) 204 5001 Scale @ A3 Zone / Mileage By www.ursglobal.com Revision Details Date Suffix EAST RIDING OF YORKSHIRE COUNCIL Check NTS East Riding of Yorkshire Council Hedon Haven Evidence Base

APPENDIX A

SITE PHOTOGRAPH LOG

Hedon Haven Baseline Study September 2013 Flood Risk 13 East Riding of Yorkshire Council Hedon Haven Evidence Base

View of the tidal defences looking north from Paull. Photograph No: 1 (Photo taken 28/6/12)

View of tidal defences looking south towards Paull. Photograph No: 2 (Photo taken 28/6/12)

Hedon Haven Baseline Study September 2013 Flood Risk East Riding of Yorkshire Council Hedon Haven Evidence Base

View of the tidal barrier at Hedon Haven (looking northeast). Photograph No: 3 (Photo taken 28/6/12)

View of the Burstwick Drain from the tidal barrier (looking east). Photograph No: 4 (Photo taken 28/6/12)

Hedon Haven Baseline Study September 2013 Flood Risk East Riding of Yorkshire Council Hedon Haven Evidence Base

Drainage ditches within the Paull Site (looking east from the tidal Photograph No: 5 barrier). (Photo taken 28/6/12)

Drainage ditch outfall into Hedon Haven (inland view). (Photo Photograph No: 6 taken 28/6/12)

Hedon Haven Baseline Study September 2013 Flood Risk