Medway LDF Core Strategy. Lodge Hill: Evidence Base. Summary Report. Flood Risk & Surface Water. Hyder Consulting

Transcription

1 Medway LDF Core Strategy Lodge Hill: Evidence Base Summary Report Flood Risk & Surface Water Hyder Consulting August 2011

2 1 Introduction 1.1 Land Securities Group Plc has been selected as the Land Sale Delivery Partner responsible for the delivery and sale of approximately 320 hectares of Ministry of Defence land at Lodge Hill. 1.2 In its role as Land Sale Delivery Partner, Land Securities Group Plc has appointed a consultant team to prepare viable and deliverable development solutions for the site, justified by robust and credible evidence, as well as sound professional judgement. 1.3 Pursuant to site investigation works and engagement with key stakeholders, the consultant team have prepared a comprehensive suite of site-specific information documents that have fed into the indicative masterplan for the development of the Lodge Hill site, which represents one way in which the site could be developed within the emerging Medway Core Strategy Plan Period (i.e. by 2028). 1.4 The purpose of the technical evidence reports, which have been prepared on behalf of Land Securities Group Plc and the Defence Infrastructure Organisation, is to support the identification of Lodge Hill as a Strategic Allocation within Medway Council s emerging Core Strategy Development Plan Document (DPD). The Core Strategy will form part of the Development Plan which provides the planning policy framework against which planning applications will be determined, to facilitate the delivery of the site. Hyder Consulting (Hyder) has contributed to the site-specific information through the production of Flood Risk and Surface Water technical evidence. 1.5 This summary report sets out the key findings and conclusions from the technical evidence prepared by Hyder which are considered essential to demonstrating the deliverability of the Lodge Hill site within the Core Strategy timescales, having regard to the guidance in PPS12 and the accompanying Plan-Making Manual. 2 Relevant Policy/Legislative Context National Planning Policy Guidance The relevant legislation is set out in the Land Drainage Act (1991), the Water Resources Act (1991) and its amendment the Water Act (2003), the Environment Act (1995), Water Framework Directive (2000), as well as the Flood and Water Management Act (2010). The Environment Agency (EA) would be a statutory 1

3 consultee on all planning matters from strategic policy formulation down to the advice on individual planning applications to the local authority. The determination of flood risk remains with the lead local flood authority. In accordance with the Environment Act (1995, Section 4), the Environment Agency's purpose is, "to protect or enhance the environment, taken as a whole" so as to promote "the objective of achieving sustainable development". Flood Risk and Surface Water have been assessed in accordance, and within the context of, the relevant legislation as well Planning Policy Statement 25 (PPS25): Development and Flood Risk. Regional Planning Policy (South East Plan) The South East Plan notes that local authorities should adopt the sequential approach to development in flood risk areas, as set out in PPS25. - The site does not lie in an identified flood risk area and as such the development is compliant with this objective. Policy NRM4 (Sustainable Flood Risk Management) requires local authorities in conjunction with the Environment Agency to, inter alia, require incorporation and management of Sustainable Drainage Systems (SUDS), other water retention and flood storage measures to minimise direct surface run-off (unless there are practical or environmental reasons for not doing so), and take account of increased surface water drainage on sewage effluent flows on fluvial flood risk. Policy KTG6 (Flood Risk) notes that the development will be planned to avoid the risk of flooding and will not be permitted if it would, inter alia, be subject to unacceptable risk of flooding or significantly increase the risk elsewhere. Policy KTG6 states that development plan documents will include policies to: Adopt a risk based approach to guiding categories of development away from flood risk areas; Ensure that development proposals are accompanied by flood risk assessments; Identify opportunities for flood storage areas to contribute to green infrastructure networks. - The development of the Lodge Hill is expected to appropriately manage the risk of flooding on site and not increase risk elsewhere. - Surface water runoff from the development can be managed on site, using sustainable drainage systems, before discharge to existing watercourses. - The development should be compliant with the above policies. Other Policies/Legislation of Relevance Medway Council is preparing a Local Development Framework (LDF) that will consist of a portfolio of documents. It will be the key spatial plan for Medway, guiding development over the period to 2028 and addressing issues relevant to the area. The first and most important of the documents is the Core Strategy, that will set out the vision, strategic objectives and an overall strategic framework for Medway. The Core Strategy is currently an emerging document. 2

4 3 Baseline Position The site is located on Lodge Hill. The topography of the site splits it into three main areas / catchments. The south-western area of the site lies on the southern side of Lodge Hill and slopes generally southwards, towards the River Medway. The remaining area of the site lies across the top of Lodge Hill, with the larger Eastern portion of this area draining to the east and a smaller Western portion draining to the west. The site is a mixture of hard surfacing and permeable areas, with the existing drainage on site consisting of a mixture of formalised piped sewers and open ditches. The site is classified as lying almost entirely within Flood Zone 1, the lowest flood risk classification. No evidence has been found to indicate that the proposed development area within the site has been affected by any historic flooding or that the site contributed to any historic flooding of downstream areas. A small part of the site, at the south west corner, is located within Flood Zones 2 and 3 (medium and high probability, respectively, of flooding from rivers and the sea). Necessary highway upgrades will be located within the onsite Flood Zone extents; however the impact of these works on flood risk can be fully mitigated on site. The proposed development is considered to pass the Sequential Test, as defined within PPS25. The ground conditions on site have been found to be primarily clay, thus the risk of flooding from ground water is considered low. The site is located on the top and side of Lodge Hill, thus there isn t a significant risk of surface water flooding from offsite sources. The redevelopment of the site will increase the volume surface water run-off generated on site. As such, there is a risk that the site itself may be a source of surface water flooding both to the site and to offsite third-party landowners. The development of a surface water management strategy for the site will ensure that the risk of surface water flooding onsite is reduced to appropriate levels and that the risk of flooding to offsite third-party landowners will not be increased. The site lies predominantly at the top of Lodge Hill, therefore the risk of fluvial flooding from minor watercourses and ditches is low. The development of the site has however the potential to increase the volume and rate of flow within the receiving offsite watercourses. 3

5 The effective management of water from the site by means of drainage infrastructure developed in accordance with the surface water management strategy should ensure the risk of the site contributing to fluvial flooding downstream from the site will not be increased. 4 Masterplan Response The development area within the site is defined as lying wholly within Flood Zone 1, thus the PPS25 Sequential Test has identified that there is no restraint on the type and location of development types (land uses) within the site (in terms of flood risk). The hierarchical management train principle of employing source, site and regional control technologies provides a methodology to utilise the most appropriate techniques sustainable drainage within developments. The current strategy of open storage ponds is one technique and the inclusion of other sustainable drainage systems (SuDS), such as green roofs, water butts, water harvesting, etc. will also be considered at further development planning stages. The inclusion of appropriate SuDS within the development will be an important ingredient towards the development achieving Code for Sustainable Homes. A preliminary surface water drainage strategy has been developed for the site and it has been demonstrated that there is sufficient space allowance within the indicative masterplan to accommodate the surface water infrastructure (in the form of ponds) assuming a 1 in 100 year plus climate change (30%) rainfall event and discharge restricted from the site to the agreed Greenfield runoff rate of 7 litres per second per hectare (l/s/ha), identified by the EA. 5 Infrastructure Delivery What, How, Where and When? The surface water drainage infrastructure serving development phases should be completed before individual development plot within the phase may be released for development. 4

6 6 Agreement with Relevant Statutory Authorities The Environment Agency has been consulted with regards to the future development of the site and have confirmed the following: - The Greenfield Runoff rate for the site is 7 l/s/ha; - With regards to existing developed areas, runoff should not exceed existing rates and where possible betterment should be included; - The surface water drainage strategy for the site should consider the 1 in 100 year plus climate change rainfall event; - The use of sustainable drainage (SuDS) is recommended wherever possible. 7 Conclusion The proposed development on site lies wholly within in Flood Zone 1, is not considered at risk of flooding, and in accordance with PPS25 is suitable for any use. The necessary highway upgrades at the south western corner of the site are located within Flood Zones 2 and 3 and the impact of these works on flood risk can be fully mitigated on site. A preliminary surface water drainage strategy has been developed in collaboration with the indicative masterplan and it has been demonstrated that the necessary surface water drainage infrastructure for the site can be delivered using sustainable drainage principles and in accordance with the requirements of the Environment Agency and the relevant national, regional and local policies. With the appropriate management of surface water on site and discharge of runoff from the site, the development should not be at risk of flooding and the flood risk to third-party landowners off site should not be increased as a result of the redevelopment. 5