Policy ENV10: Managing Flood Risk

Open22 Jan, 2024, 10:00am - 4 Mar, 2024, 11:59pm

Policy ENV10:  Managing Flood Risk

The sequential approach to development, as set out in national guidance, will be applied across the borough, taking into account all sources of flooding as contained within the council’s Strategic Flood Risk Assessment (SFRA). Development within areas of flood risk from any source of flooding[1] will only be acceptable if it is clearly demonstrated that it is appropriate at that location, development will be safe from flooding and not increase the risk of flooding elsewhere, and that there are no suitable available alternative sites at a lower flood risk. Development proposed in an area at risk of flooding will be required:

  1. To be supported by a Flood Risk Assessment[2] (FRA) (subject to the triggers in national guidance and set out below);
  2. To clearly demonstrate that the benefits of the development to the community, outweigh the risk of flooding when applying the sequential test and exception test (where required);
  3. When applying the sequential test, to clearly demonstrate that the impacts of climate change are taken into account as identified in the SFRA (and in any subsequent information provided by the Environment Agency or LLFA);
  4. To provide a safe access and egress route up to a 1 in 100 year flood event plus climate change allowance; and
  5. To attenuate surface water run-off on the site so that the run-off rate is no greater than existing for a greenfield site or, if the site is previously developed, development actively reduces run-off rates and volumes as close as practicably possible to greenfield rates.

The triggers for an FRA are:

  • All sites of 1 ha or more in Flood Zone 1;
  • All Sites in Flood Zone 2 or 3;
  • Land which has been identified by the Environment Agency as having critical drainage problems
  • Land identified in a SFRA as being at increased flood risk now and in the future
  • Land that may be subject to other sources of flooding where its development would introduce a more vulnerable use [3]
  • Sites that have a record of localised or groundwater flooding from the SFRA (and any subsequent records of flooding reported to the Lead Local Flood Authority or water company);
  • Sites in Local critical drainage areas and upstream of Local critical drainage areas .

All planning applications for major development are required to ensure that Sustainable Drainage Systems (SUDs) are used for the management of surface water unless demonstrated to be inappropriate. All new developments in areas at risk of flooding must give priority to the use of sustainable drainage systems. Details of the design, construction, maintenance, operation and adoption of the SUDs over the lifetime of the development (a SuDS Strategy) shall be included with the proposal and implemented accordingly.

Any development proposed within a flood risk priority area identified in Hampshire County Council’s Catchment Management Plans, will be expected to comply with the policy statements in those Plans (and any updates and future action plans). Opportunities to reduce the causes and impacts of flooding within the borough through development should be taken.

Developers will be expected to engage early with the relevant water company to ensure that the necessary infrastructure is delivered alongside the development.

7.71 Analyses of the flood zones within the borough, undertaken as part of the SFRA, indicate that about 2.8% of the borough is within the floodplain (i.e. within the areas covered by Flood Zones 2, 3a and 3b). A potential risk of flooding from various sources exists throughout the borough including fluvial flood risk, groundwater flooding, sewer surcharge and surface water flooding, and changing climate patterns are likely to have a substantial impact on the level of flood risk from all sources. Groundwater flooding poses the most significant risk to the borough due to the bedrock geology. As well as resulting in direct flooding, it is also a contributing factor to fluvial and surface water flooding events.
7.72 For all new development, the sequential approach has to be followed in accordance with national guidance (2021).
7.73 Windfall development proposed in areas of high flood risk will only be acceptable if it can be demonstrated sequentially that there are no preferable sites in areas at lower risk, development would not increase the risk of flooding elsewhere and that the sequential approach to site layout has been followed. Where developments provide sustainability benefits to the community, for example the provision of affordable housing on a rural exception site, this benefit may outweigh the risk of flooding when applying the sequential test. Each case would however be considered on its own merits and would be balanced against the specific flood risks associated with the location and vulnerability of the proposed development. Depending on the vulnerability of the proposed use, the exception test may also need to be met.
7.74 National guidance requires the submission of a site-specific FRA for all sites in Flood Zone 2 and 3 for all sites greater than 1 hectare within Flood Zone 1 and for sites less than 1 hectare in certain circumstances. Applicants are advised to refer to the requirements of national guidance, information in the SFRA 2021 and general standing advice for developers/applicants in this regard. The content of the FRA will vary depending on the scale and nature of the development, and the source of the flooding, and can range from a brief report to a more detailed assessment. The SFRA provides a checklist and further information on what needs to be included within an FRA. It also provides guidance on the range of measures that could be considered on site in order to manage and mitigate flood risk, including a sequential approach to layout.
7.75 The SFRA for the borough identifies locations at risk of fluvial, groundwater, and surface water flooding now and in the future. It also identifies locations that have experienced localised flooding and locations where a new development is likely to overload the capacity of the existing drainage system. These areas have been identified in the SFRA as ‘local critical drainage areas’ and are highlighted in the SFRA Flood Maps. Areas which drain into the ‘local critical drainage areas’ have also been identified as part of this study as ‘upstream of local critical drainage areas’ and are also highlighted in the SFRA Flood Maps. It is expected that an FRA will also be provided for development in these locations. Information on flood risk is being updated continuously and flood risk information should always be used to inform planning applications, including future SFRA’s and the Environment Agency’s flood map for planning and surface water flood risk information.
7.76 All greenfield site allocations will be required to manage surface water run-off as part of an overall strategy demonstrating that surface water is attenuated to that of Greenfield run-off rates. Sustainable drainage systems can help to reduce the overall amount of rainfall being discharged to the drainage system from new development and help to reduce surface water flooding risks. The government has published guidance on technical standards relating to the design, construction, operation and maintenance of sustainable drainage systems. It is expected that drainage systems will be effectively implemented alongside the development and maintained for the duration. In considering planning applications, the local planning authority will consult the Lead Local Flood Authority (Hampshire County Council) on the management of surface water including on sustainable drainage systems and CIRIA have published guidance on the construction of SuDS[4]. HCC has produced guidance on Sustainable Drainage Systems (2018). Proposals should maximise the use of natural flood management techniques, which incorporates opportunities for green infrastructure, biodiversity and improved water quality, as part of an integrated approach to flood risk management. The SFRA identifies opportunities to reduce the causes and impacts of flooding such as through natural flood management and river restoration.
7.77 Developments will be expected to comply with the underlying principles and policies set out in the Hampshire Local Flood and Water Management Strategy and Catchment Management Plans (and any associated action plans) which identify and prioritise areas that are at an increased risk of flooding due to geographical, geological or development features.
7.78 This policy aims to achieve a planning solution to flood risk management wherever possible, steering vulnerable development away from areas affected by flooding. Where there is no alternative to development being located in an area at risk of flooding, the policy sets out specific requirements to minimise the risk.
Implementation and Monitoring

The policy will be implemented through:

  • Advice on, and the determination of, relevant planning applications by the council, the Environment Agency and the Lead Local Flood Authority (LLFA).

The policy will be monitored through:

  • Working in partnership with the Environment Agency, Water Companies, Natural England and the Lead Local Flood Authority (LLFA)
  • Annual monitoring of development completions within flood zones 2 and 3
  • Updates to the SFRA
  • Surface Water Management Plans

[1] Flood zone 2 and/or 3, an area that has experienced localised or ground water flooding, at medium or high risk of surface water flooding based on the EA long term flood risk map, areas where incidents of sewer flooding have previously been reported, or a site within or upstream of a Local Critical Drainage Area.

[2] The minimum requirements for an FRA are set out in the council’s Strategic Flood Risk Assessment and any subsequently updated version in addition to national advice.

[3] The Flood Risk Vulnerability Classification is set out in the NPPF.