HARBOURS ACT 1964 (AS AMENDED) THE POOLE HARBOUR REVISION (WORKS) ORDER 2014 ENVIRONMENTAL STATEMENT VOLUME 4: FLOOD RISK ASSESSMENT

Transcription

1 Intended for Poole Harbour Commissioners Report Reference 19463/ENV/R12 Date May 2014 FINAL HARBOURS ACT 1964 (AS AMENDED) THE POOLE HARBOUR REVISION (WORKS) ORDER 2014 ENVIRONMENTAL STATEMENT VOLUME 4: FLOOD RISK ASSESSMENT

2 CONTENTS 1. INTRODUCTION SCOPE AND OBJECTIVES 1 2. SITE CONTEXT AND BASELINE CONDITIONS SITE LOCATION AND SURROUNDING USE GEOLOGICAL SETTING HYDROLOGICAL SETTING HYDROGEOLOGICAL SETTING EXISTING DRAINAGE FLOOD RISK 4 3. POTENTIAL IMPACTS OF PROPOSED DEVELOPMENT DESCRIPTION OF THE PROPOSED DEVELOPMENT FLOOD RISK MANAGEMENT STRATEGY SHORELINE MANAGEMENT PLAN WAVE MODELLING SURFACE WATER RUNOFF FLOOD RISK VULNERABILITY DRAINAGE STRATEGY CONCLUSION 10 FIGURES FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 SITE LOCATION PLAN EXISTING SITE LAYOUT PROPOSED DEVELOPMENTS ENVIRONMENT AGENCY INDICATIVE FLOODPLAIN MAP (contained in report) DIFFERENCE IN WAVE HEIGHT BETWEEN EXISTING AND PROPOSED LAYOUT (contained in report)

3 1 1. INTRODUCTION Ramboll has been appointed by Poole Harbour Commissioners (the 'applicant') to undertake an Environmental Impact Assessment (EIA) for the elements identified in the Port of Poole Master Plan that relate to the development and modernisation of the commercial port infrastructure (hereafter referred to as the 'proposed developments'). The proposed developments are located in Poole Harbour wholly within the boundary of the Borough of Poole (hereafter referred to as the 'BoP'). The proposed developments are described in Section 2 of the Environmental Statement This Flood Risk Assessment (FRA) forms one in a series of supporting documents to the EIA Environmental Statement (ES) and as such should be read in conjunction with the ES (Report Reference 19463/ENV/R03) The following information sources were used to prepare this report: Works extent drawings prepared by Poole Harbour Commissioners (Figure 3, Proposed Development drawing); British Geological Survey (BGS) maps; Borough of Poole Strategic Flood Risk Assessment (SFRA) (Level 1, January 2009, and Level 2, July 2008); Borough of Poole Flood Risk Management Strategy (FRMS) (Report No 9V4473, January 2011); National Planning Policy Framework (NPPF) (2012) and Planning Practice Guidance: Flood Risk and Coastal Change (2014); Environment Agency (EA) online database of indicative floodplain and hydrogeological maps; and HR Wallingford (HRW) report Hydrodynamic and Sedimentological Studies (Report reference DDR5073-RT001-R05-00, 2014) Ramboll cannot accept any liability for the accuracy or otherwise of any information derived from third party sources. 1.1 Scope and Objectives This document considers the risks of various sources of flooding, predominantly to the site itself, but also the consequent risk of flooding to downstream receptors (such as people, property, habitats, infrastructure and statutory sites) as a result of the proposed developments, from surface water runoff. A comparison is made between the current situation and the proposed developments including an allowance for the effects of climate change This FRA has been carried out in accordance with the National Planning Policy Framework (NPPF) and the associated Planning Practice Guidance. It is to be used to assist the Marine Management Organisation (MMO) and the EA, when considering the flooding issues of the proposed developments, as part of an HRO application This report provides the following information: i. An assessment of the flood risk to the development site based upon flood data and the flood maps provided by the EA, SFRA and FRMS; ii. An assessment of flood risk to the development site from changes in the wave climate caused by the proposed developments based on modelling undertaken by HRW; iii. An assessment of the impact of the proposed developments in terms of surface runoff; iv. Proposals for measures to mitigate the generation of surface water runoff from the proposed developments; and v. Proposals to mitigate any residual flood risks to the proposed developments (if any).

4 2 2. SITE CONTEXT AND BASELINE CONDITIONS 2.1 Site Location, Surrounding Use and Development Plan The Port of Poole is a Trust Port established in 1895 and managed by Poole Harbour Commissioners (PHC). The Port is located at approximately National Grid Reference SZ on the northern shore of Poole Harbour, a large semi-enclosed water body on the central south coast of the United Kingdom (UK). The Port occupies the western side of the shoreline adjacent to the Backwater Channel, which connects Holes Bay with the main Harbour water body. The main commercial, retail and residential areas of Poole lie to the north east of the Port, across the Little Channel, whilst the residential and commercial areas of Hamworthy occupy the peninsula on the western side of the channel to the north west of the Port. The existing commercial Port is linked to the town by both Poole Bridge and Twin Sails Bridge, which opened in April The Port currently runs commercial operations from approximately 24 hectares of land, with cross-channel freight and passenger Ro-Ro ferries as well as conventional bulk cargo vessels utilising the Port. In addition, PHC run two marinas, one to the south east of the Port area (Port of Poole Marina), and one off Poole Quay (Poole Quay Boat Haven). The Port also hosts visiting cruise ships throughout the year. Please see Figure 1 for a Site Location Plan and Figure 2 for an Existing Site Layout Plan A Master Plan for the proposed development of the Port over the next 25 years was prepared and adopted by the Poole Harbour Commissioners in March This Master Plan includes proposals for a number of new and improved facilities which would be delivered separately over the period covered by the Master Plan. Consent for the proposed developments in the Master Plan will be applied for via Harbour Revisions Orders (HROs) from the Marine Management Organisation (MMO). This report forms part of the application for consent for all proposals in the Master Plan attached to the existing commercial Port The HRO proposes a series of works (works 1 to 10, as set out in the HRO) in five phases of development as follows: Phase 1 (HRO works 1 and 2): The creation of South Quay, a new 180m long deep water south-facing quay dredged to 9.0m Below Chart Datum (BCD), to be used by a variety of craft such as cruise ships, small container feeder ships, bulk cargo vessels, and possibly wind park construction vessels. This development would require approximately 8,000m 2 of reclamation and allow for the retention of the Port of Poole Marina; Phase 2 (HRO works 3 and 4): Increase the width of South Quay by a further 20m and develop 120m of east-facing berth (East Quay) dredged to 7.5m BCD. This development would produce a further 7,000m 2 of reclamation, reducing the capacity of the Port of Poole Marina; Phase 3 (HRO works 5 and 6): Deepening of existing conventional quays including Ballast Quay, Bulwark Quay, New Quay and New Quay extension to 7.5m BCD (referred to in the adopted Master Plan as Proposal C ), with minor modifications to the line of the existing quays including raising the coping to address flood defence considerations and creating 2,600m 2 of reclaimed land; Phase 4 (HRO works 7 and 8): Completion of East Quay, extending northwards to join New Quay extension, eliminating the Port of Poole Marina and creating a further 22,000m 2 of operating land. (This scheme is referred to as Proposal B in the adopted Master Plan); Phase 5 (HRO works 9 and 10): Reconstruction of the existing Ro-Ro berths to facilitate deeper drafted vessels. This would involve a berthing face of 350m dredged to 9.0m BCD. The footprint of reclamation for this development would be 5,000m 2.

5 The proposed developments are shown on Figure For the purposes of the EIA this Technical Annex has assessed a worst case scenario which assumes that all of the above developments will come forward at some point during the life of the Master Plan. The HRO that this EIA accompanies, however, will seek permission for all of the developments described above, with the appropriate licences and permissions being applied for as and when required. An initial construction programme has been identified in Table 1 below. Table 1: Initial Construction Programme Total Contract Duration Potential Project Start Date Phase 1 South Quay Phase 2 Extension of South Quay Phase 3 Deepening Conventional Quays Phase 4 Completion of East Quay & infill Port of Poole Marina Phase 5 Reconstruction RoRo berths 6-9 months 6-9 months 4-6 months 4-6 months 4-6 months Jan 2015 Jan 2017 Jun 2017 Jan 2018 Jan For further information on the proposed developments, including construction principles, please refer to the Environmental Statement (19463/ENV/R03). 2.2 Geological Setting The British Geological Survey (BGS) online geological maps show the northern shore of Poole Harbour to be underlain by Oakdale Clay Member typically sands with some silty clay further inland. These are sedimentary bedrock formed approximately 24 to 29 million years ago in the Palaeogene Period typically in marginal coastal plains with lakes and swamps periodically inundated by the sea The overlying superficial deposits comprise beach deposits and sands. These were formed up to two million years ago in the Quaternary Period due to the shoreline environment where sediments are deposited in beaches and barrier islands. 2.3 Hydrological Setting The development site is located on the northern shore of Poole Harbour, a semi-enclosed water body connecting Holes Bay to the main Harbour water body. The Harbour is shallow, with one main dredged channel through the Harbour, from the mouth to Holes Bay The entrance to Poole Harbour is from the east, via Poole Bay and the English Channel located approximately 4km south-east of the development site at the nearest point. On either side of the Harbour entrance is the shores of Studland beach and Sandbanks. Inside the Harbour mouth are several islands, the largest of which being Brownsea Island. 2.4 Hydrogeological Setting The EA has developed Groundwater Source Protection Zones to assist in the assessment of risk to groundwater supplies taken from an abstraction point. The development site does not lie within a Groundwater Source Protection Zone There are no surface water or groundwater abstractions within 500m of the development site.

6 The EA website also shows aquifers and provides designations which are in line with the Water Framework Directive and are based on maps produced by the BGS. The geology beneath the development site is designated as a Secondary A Aquifer in the superficial deposits and bedrock. Definitions for the aquifer types are provided below based on the EA website: Principal Aquifer: layers of rock or drift deposits that have high intergranular and/or fracture permeability meaning they usually provide a high level of water storage. They may support water supply and/or river base flow in a strategic scale. Secondary A Aquifer: permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. Secondary B Aquifer: predominantly lower permeability layers which may store and yield limited amounts of groundwater due to localised features such as fissures, thin permeable horizons and weathering. These are generally the water-bearing parts of the former nonaquifers. Secondary Undifferentiated Aquifer: it has not been possible to attribute either category A or B to a rock type. In most cases, this means that the layer in question has previously been designated as both minor and non-aquifer in different locations due to the variable characteristics of the rock type. Unproductive Strata: rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow Groundwater levels at the development site are thought to be very high because of the low ground levels and presence of the sea as a natural control. Because of this, infiltration levels are likely to be very low. 2.5 Existing Drainage Surface water runoff from impermeable areas within the current Port of Poole marina and Port is channelled into Poole Harbour. 2.6 Flood Risk There are a number of key potential sources of flooding that can put sites at risk. These include fluvial (rivers), tidal (the sea), groundwater, sewer, surface water and infrastructure failure (including reservoirs, canal, industrial processes, burst water mains and blocked sewers or failed pumping stations) The major risk will be from tidal flooding by wind driven waves during Spring tides in a low pressure system. This is the key consideration taken in reviewing flood risk to the development site and the surrounding area. Fluvial and Tidal Table 2: Current Tidal Levels (mcd) MHWS MHWN MLWN MLWS Spring Range Neap Range Source: Admiralty Chart Current tidal levels are given in Table 2. Significant day-to-day variability occurs in the tidal levels, with these values being indicative only.

7 The EA indicative floodplain maps identify areas in England and Wales at risk of flooding by allocating them into flood risk zones. The flood risk zones shown on the flood maps are defined in Table 1 of the NPPF Planning Practice Guidance: Flood Risk and Coastal Change: Zone 1: Low Probability According to the NPPF, land in this zone is considered to have less than 1-in-1000 annual probability of river or sea flooding in any year. This is <0.1%. Zone 2: Medium Probability According to the NPPF, land in this zone is considered to have between a 1-in-100 and 1-in annual probability of river flooding in any year (between 1% and 0.1%) or between a 1-in-200 and 1-in-1000 annual probability of sea flooding in any year (0.5% to 0.1%). Zone 3a: High Probability According to the NPPF, land in this zone is considered to have a 1-in-100 or greater annual probability of river flooding in any year (>1%) or a 1-in-200 or greater annual probability of flooding from the sea in any year (>0.5%). Zone 3b: The Functional Floodplain According to the NPPF, land in this zone is used for water flow or storage in times of flood. This flood zone should be identified by a Strategic Flood Risk Assessment (SFRA). It is considered to have a 1-in-20 or greater chance of river flooding in any year which is >5%. Another probability, however, can also be agreed between the LPA and the EA The EA Indicative Floodplain Map takes into account prediction for climate change and sea level rise. EA reports indicate that the Mean Sea Level at Poole is due to rise 1.26m in the next 116 years, consequently increasing the risk to many areas of the town The EA Indicative Floodplain Map shows that New Quay, Ballast Quay and Bulwark Quay are within Flood Zone 3a, at significant risk of flooding from the sea assuming there are no defences present, although the bulk of the land area of the Port of Poole is within Flood Zone 1. The EA Indicative Floodplain Map is provided in Figure In addition to making use of this data when considering flood risk, some specific modelling was undertaken by HRW which is discussed in section 3.4.

8 6 Figure 4: EA Indicative Floodplain Map Flood Defences There are no formal defences shown on the EA map on the south western shore of Back Water Channel, although the quay walls will act in this capacity until overtopped In the Borough of Poole FRMS the Port of Poole area is considered as a single area, Cell 2c. The policy for this area is to Hold the Line of the current coastline (a similar conclusion is reached in the SFRA). Although there are no specific guidelines or modelling given for this area, general calculations for the Port indicate that the 1-in-200 flood level estimate is 1.85mAOD, which is equivalent to 3.25mCD, and a freeboard of 0.7m is advised above this level, bringing the advisory flood defence level to 3.95mCD or 2.55mAOD. Surface Water and Sewer Drainage Surface water flooding in the local area can be caused by tidal locking and high groundwater, which can cause reduced capacity and overspill sewers and surface water drains. The SFRA details records of a number of flood events over the last ten years. However, it is considered that the Poole area has not been subject to significant flooding as the events that have occurred have been of a relatively low return period. Groundwater Groundwater levels at Poole are strongly controlled by sea level, and will not cause an independent flood event. However, high groundwater levels can contribute to fluvial and surface water flooding events.

9 7 Artificial Water Bodies There are no reservoirs or artificial water bodies located so that a failure could cause flooding in the area of the development site. Flood Risk Summary Table 3 summarises the flood risk to the development site from various sources. Table 3: Potential Flooding Sources for the Development Site Tidal/fluvial Surface water and drainage flood risk Groundwater Reservoirs, canals and other artificial sources High Medium Low X X X X Large areas of the development site are within Flood Zone 3 due to tidal flood risk Tidal locking can cause surface water flood events Groundwater levels are controlled by sea levels No nearby artificial water sources

10 8 3. POTENTIAL IMPACTS OF PROPOSED DEVELOPMENTS 3.1 Description of the Proposed Developments The proposed developments have been described in section 2.1. Figure 3 shows the proposed developments. 3.2 Flood Risk Management Strategy Elements from the Borough of Poole FRMS have been discussed already in Section The proposed developments incorporate works to improve the local flood defences, which is in accordance with the strategic planning for the area. The quay wall levels will be 4.0mCD in order to exceed the level advised in the FRMS (3.95mCD) and tie into other local levels, with the South Quay level being 4.5mCD in order to offer additional capacity against wave overtopping. This higher level will also offer additional protection for the Port from extreme weather events, e.g. storms. 3.3 Shoreline Management Plan The policy outlined in the Shoreline Management Plan for the north shore of Poole Harbour, including the main Harbour, and other built-up areas, is to maintain the current shoreline by maintaining current defences or, if necessary, developing new flood defences for these areas. 3.4 Wave Modelling HRW has modelled the operational and extreme wave conditions for the existing scenario and the one defined by the proposed developments. Since Poole Harbour is sheltered from offshore waves by its narrow entrance and the position of Brownsea Island, the local wind climate is the main wave generator The HRW model is based on a Mean Sea Level (MSL = 1.6m CD) and Mean High Water Springs (MHWS = 2.2mCD) at present day The modelling results indicate that the proposed developments will have little to no effect on the wider wave environment of Poole Harbour, with minor changes confined to the local area of the development site.

11 In certain extreme scenarios some wave height changes are seen in small areas compared to the baseline. This is identified for instance in front of the new South Quay in wave conditions such as that shown in Figure 5, but these are not considered to be of concern because the physical alignment of the quay has changed and as such the net change in wave level at that specific location will have a corresponding change. The change identified in the figure can therefore appear misleading if not considered in combination with the physical changes of the quay alignment that the model has simulated. Figure 5: Difference in Wave Height (m) between Existing and Proposed Layouts with 1-in-100 Years Condition with Wind Direction from 240N and MHWS Taken from HR Wallingford report Hydrodynamic and Sedimentological Studies (Report reference DDR5073-RT001-R05-00, 2014) 3.5 Surface Water Runoff The proposed developments include the potential for up to 37,000m 2 of new impermeable area ( filling in the existing Port of Poole marina). However, although this will result in an increase in surface water runoff there is no requirement for attenuation as the proximity of the Harbour means the water can most easily be naturally attenuated in the sea; there are no downstream areas that could have their flood risk affected by the proposed developments. It must also be considered that rainfall pre-development would fall directly into the Harbour itself and therefore pre and post development scenarios do not alter the amount of rainwater reaching the Harbour Some local source control may be required in areas where contaminants such as hydrocarbons may be present, for instance boat fuelling areas, to prevent contaminant chemicals reaching receptors within the Harbour.

12 Flood Risk Vulnerability According to Table 2 (Flood Risk Vulnerability Classification) in the NPPF Planning Practice Guidance: Flood Risk and Coastal Change, the proposed developments are classified as Water- Compatible. In accordance with Table 3 (Flood Vulnerability and Flood Zone Compatibility) Water-Compatible development is considered appropriate within Flood Zone 3a. 3.7 Drainage Strategy It is proposed to drain surface runoff from the impermeable areas of the proposed developments via a separator into the Harbour using gullies and a piped network with outfalls as required in the quay walls.

13 10 4. CONCLUSION The proposed developments include new quays, modifications to the existing quays, and reclamation from the existing Port of Poole Marina. New quay walls will be constructed to level that satisfies the requirements of the Borough of Poole FRMS for the area and this approach is deemed acceptable by the EA Parts of the development site are situated within Flood Zone 3, at high risk of tidal or fluvial flooding. However the proposed developments are classified less vulnerable to flooding, which according to the NPPF Planning Practice Guidance: Flood Risk and Coastal Change Table 3 (Flood Risk Vulnerability and Flood Zone Compatibility ) is appropriate within Flood Zone Because of the existing uses at the development site, there is no formal surface water drainage system present. Water runs straight off the existing marina and quayside surfaces into the Harbour It is proposed to continue to allow surface water runoff to enter the Harbour in a natural fashion, using channels, gullies and a piped system to direct the flow via a separator to discharge to the Harbour On the basis of this report, since the development is extremely resilient to flooding, no further FRA will be required for this scheme.

14 FIGURES FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 SITE LOCATION PLAN EXISTING SITE LAYOUT PLAN PROPOSED DEVELOPMENTS ENVIRONMENT AGENCY INDICATIVE FLOODPLAIN MAP (contained in report) DIFFERENCE IN WAVE HEIGHT BETWEEN EXISTING AND PROPOSED LAYOUT (contained in report)

15 Legend Extent of Proposed Works Area Shown in Main Map Ü Kilometers Crown copyright and database rights 2014 Ordnance Survey Client Poole Harbour Commissioners Project Title Harbours Act 1964 (as amended) The Poole Harbour Revision (Works) Order 2014 Project Number Figure Title Site Location Plan Tel: Fax: Date Reproduced from OS map data by permission of the Ordnance Survey. Licence No: ,000 2,000 3,000 4,000 m Figure No. 11/02/14 1 southampton@ramboll.co.uk Prepared By CL Revision 2

16 Legend Extent of Proposed Works Port Estate Boundary Note Details of the Proposed Works are shown in Figure 3 Bulwark Quay Poole Quay Boat Haven Ü Meters Contains Ordnance Survey data Crown copyright and database right 2014 Poole Yacht Club Ferry Car Lanes Car Park Ro-Ro Freight Cargo Handling Ro-Ro Berths Cargo Handling Port of Poole Marina Jetty Client Project Title Harbours Act 1964 (as amended) The Poole Harbour Revision (Works) Order 2014 Project Number Figure Title Poole Harbour Commissioners Existing Site Layout Tel: Fax: southampton@ramboll.co.uk Reproduced from OS map data by permission of the Ordnance Survey. Licence No: m Date 31/03/13 Figure No. 2 Prepared By CL Revision 3

17 Legend Port Estate Boundary Limit of Dredge Assessed Extent of Proposed Works Extent of Proposed Quay HRO Development Phases 1 Construction 1 Dredge 2 Construction Ballast Quay Bulwark Quay Poole Quay Boat Haven 2 Dredge 3 Construction 3 Dredge 4 Construction 5 Construction 5 Dredge Port of Poole Marina New Quay Ü Meters Contains Ordnance Survey data Crown copyright and database right 2014 Client Project Title Harbours Act 1964 (as amended) The Poole Harbour Revision (Works) Order 2014 Project Number Figure Title Poole Harbour Commissioners Proposed Developments Tel: Fax: southampton@ramboll.co.uk Date 12/02/14 Figure No. 3 Prepared By MJC/CL Revision 2