Development and Flood Risk

Flooding from rivers and coastal waters plays an important natural process which helps shape the natural environment, however flooding can threaten life and cause substantial damage to property. Although flooding cannot be wholly prevented, its impacts can be avoided and reduced through good planning and management.

There is approximately 35km of tidal frontage in Southampton including the lower reaches of the city’s two main rivers, the River Test and River Itchen, which join together to form Southampton Water. The tidal influence of these rivers extends through the administered boundary of the city. There are also a number of smaller rivers in Southampton, namely Tanners Brook, Holly Brook, Rolles Brook, Monks Brook, Jurds Lake and Bligmont Crescent Stream. At present, approximately 10% of the city is identified as being at high or medium risk of flooding from these sources.

Due to the urban nature of Southampton, the city is also at risk from surface water flooding. This is where water is unable to soak into the ground or enter the drainage system after periods of heavy rainfall. Other sources of flooding include groundwater and risk from artificial sources such as reservoirs; however these pose less of a risk to Southampton, despite being less predictable.

Any future development within areas where there is a flood risk will need to be designed for any flooding over the lifetime of the development and be able to manage the effects of flooding to ensure the development is safe. The documents below set out detailed information on the relevant sources of flood risk facing Southampton both now and in the future, and the requirements developers must meet.

Partnership for Urban South Hampshire Strategic Flood Risk Assessment (Push SFRA)

The Partnership for Urban South Hampshire (PUSH) commissioned a joint Strategic Flood Risk Assessment (SFRA) for the sub-region which was prepared in accordance with Planning Policy Statement 25: Development and Flood Risk (PPS25). The SFRA is a critical part of the evidence base for the sub region and enables the Local Planning Authorities within the PUSH sub-region to make informed decisions on the allocation of land for development in their Local Development Frameworks. The PUSH SFRA was completed in December 2007. The final reports and series of maps can be accessed via the PUSH SFRA link below.

Level 2 Strategic Flood Risk Assessment (SFRS)

The Level 2 SFRA, which progresses and updates the PUSH SFRA, was completed in partnership with the Environment Agency. The series of documents provide detailed information on the nature of flood risk, both current and future, from all sources across the city, including coastal, river, surface water and groundwater.

The primary objective of the Level 2 SFRA is to provide Southampton City Council with sufficient information to comprehensively apply the requirements of Planning Policy Statement 25 (PPS25): Development and Flood Risk, and to satisfactorily inform the relevant Local Development Documents of the Local Development Framework. It also identifies a range of potential strategies to manage flood risk and adapt to climate change on major development sites located within flood risk areas. The Level 2 SFRA was completed in September 2010 and can be downloaded from the downloadable documents section at the end of this page.

Flood Risk Assessment Guidance – More Vulnerable Development

The Flood Risk Assessment (FRA) Guidance for more vulnerable development (as defined by PPS25) was produced to assist developers and applicants when dealing with the control and mitigation elements of the flood risk management hierarchy (outlined in the PPS25 Practical Guide) in order to manage flood risk and ensure new development is safe. A copy of the guidance document is available to download at the bottom of this page.

Site Flood Plan – Guidance and Templates

Complementary to the FRA guidance, the Emergency Planning team have produced the Site Flood Plan (SFP) overview and template documents. A site flood plan will be required where it is not feasible to achieve safe access/egress to the development site and must outline how users of the site can avoid danger from hazards should a flood event occur. Both the guidance and template documents can be downloaded from the documents section below.

Sustainable Drainage Systems (SuDs)

In order to manage surface water, developers are encouraged to implement sustainable drainage into new development. Planning Policy Statement 25 (Annex F) states that ‘it will always be much more effective to manage surface water flooding, at and from, new development early in land acquisition and design process rather than to resolve problems after development’.

The management of surface water should be demonstrated as part of the Site Specific Flood Risk Assessment ensuring the proposed drainage system will reduce flood risk to the site itself and elsewhere, taking climate change into account. A guide for developers on achieving sustainable drainage is available to download from the downloadable documents section of this page and further information on the implementation of SUDS is available from the CIRIA website by following the link below.