CS9 - Flooding
Flooding has implications for Woking Borough, not only in terms of the constraint it places on the location of new development, but it is also an issue which relates to climate change. This threatens the livelihood of residents and local businesses, the floods of 2000 being a reminder of that.
Flooding within the Borough originates from a number of sources. The most serious are river, surface water flooding and sewer inundation. With advice from the Environment Agency, the Council has undertaken a Strategic Flood Risk Assessment (SFRA - available on the Council's website) in order to have a comprehensive understanding of the source and level of flood risk within the Borough and provide a basis against which to apply the PPS25: Development and flood risk sequential approach to development. This document will be used to inform the Site Allocations DPD. It has also been used to inform the preparation of the Strategic Housing Land Availability Assessment (SHLAA) and contains advice for developers on undertaking Flood Risk Assessments. In addition, it takes on board other relevant plans and strategies relating to the management of flood risk.
Water quality impacts on wildlife in and around water, public health and the appearance and amenity of watercourses.
The Council will determine planning applications in accordance with the guidance contained within PPS25: Development and flood risk. The SFRA will inform the application of the Sequential and Exceptional Test set out in Annex D of PPS25.
The Council expects development to be in Flood Zone 1 as defined in the SFRA. Applications or allocations within Flood Zone 2 will only be considered if it can be demonstrated that there are no suitable alternatives in areas at lower risk. The Council will not encourage development in Flood Zones 3a and 3b. However, it accepts that this is possible in exceptional circumstances. Development proposals in Flood Zones 3a and 3b will be required to be accompanied by a comprehensive Flood Risk Assessment to demonstrate that the development will not increase flood risk elsewhere or exacerbate the existing situation.
The Council will require all significant forms of development to incorporate appropriate sustainable drainage systems (SUDS) as part of any development proposals. If this is not feasible, the Council will require evidence illustrating this.
A Flood Risk Assessment will be required for development proposals within or adjacent to areas at risk of surface water flooding as identified in the SFRA. To further reduce the risk from surface water flooding, all new development should work towards mimicking greenfield run-off situations.
Proposals which relate specifically to reducing the risk of flooding (e.g. defence/ alleviation work) will be supported so long as they do not conflict with other objectives of the Core Strategy for example, those relating to landscape and townscape character.
In areas at risk of flooding, proposals (including flood compensation proposals) with implications for biodiversity will be carefully considered for all levels of ecological designation. Where the development proposals are demonstrated to adversely affect an SPA, SAC or RAMSAR site, permission will not be granted.
The Council has undertaken a Strategic Housing Land Availability Assessment in order to identify sufficient land with housing potential to meet its development requirements. The current assessment highlights that there is sufficient land outside of Flood Zone 3a or 3b to meet the Borough's housing requirements. In addition, and in accordance with the sequential approach, Flood Zone 2 will only be considered if sufficient housing land supply cannot be identified in Flood Zone 1 to meet the housing target and all suitable alternatives have been considered. It will not be necessary to permit development in Flood Zone 3a or 3b. However, applications for replacement properties in these locations will be considered providing that there is a similar or reduced built footprint and measures to reduce flood risk will be expected.
Applicants will be required to undertake a Flood Risk Assessment for development proposals within or adjacent to areas at risk from surface water run off. The SFRA identified areas of potential risk, although circumstantial evidence will be considered on a case-by-case basis. National policy (PPS25: Development and flood risk) also requires Flood Risk Assessments for all development proposals in Flood Zones 3a, 3b and 2 as well as all development proposals of one hectare or above in Flood Zone 1. Where there is potential for other sources of flooding, a Flood Risk Assessment should be considered to investigate the level and impact of the risk and propose mitigation measures in accordance with the advice in PPS25 and the Council's SFRA. Applicants will be encouraged to recognise the benefits that undertaking a Flood Risk Assessment can bring to a development, even if not required.
A sequential approach to development will be applied for Flood Zones 3a and 3b.
In managing surface water run-off from development sites, applicants should work towards replicating greenfield run-off situations. In order to achieve this, priority should be given to prevention of surface water runoff (e.g. through minimising paved areas, keeping drains clear, general maintenance), followed by source control measures. On-site solutions such as infiltration devices, filter strips should then be sought and only if these will not satisfactorily deal with the run-off should off-site solutions be considered (such as discharge into water courses). These requirements are complemented by Building Regulations and considerable guidance is also available via CIRIA (Construction Industry Research and Information Association).
The policy will be delivered in the following ways:
- Working with the Environment Agency, Surrey County Council, and the water authorities to keep the SFRA updated, showing the latest known position on flooding and areas at risk.
- The Council will continue to collect information on flooding incidents affecting properties, business premises and the transport network, which will be fed into updates of the SFRA.
- A Surface Water Management Plan is being prepared with Surrey County Council. The plan aims to identify viable options to manage the risk of surface water flooding, for the benefit of Woking and Byfleet and its people, both now and in the future.
Monitoring and review
The following indicators will be used to monitor the effectiveness of the policy.
- The number of planning permissions granted contrary to Environment Agency / Water Authority advice and for what reasons.
- The number of new properties in Flood Zones 2, 3a and 3b.
- The number of new developments incorporating sustainable urban drainage systems (SUDs).
Key evidence base
Strategic Flood Risk Assessment, 2009, produced by Capita Symonds.