Establishing flood risk strategies

Coastlines, rivers and catchments often form or cross boundaries and therefore need to be planned for and approached strategically.

Effective flood risk management needs to take into account strategic environmental impacts in the management of river catchments and coasts. This includes recognising the primary role of floodplains in the management of extreme rainfall events, linked with river restoration across catchment boundaries.

Riparian owner rights – the legal rights of owners adjacent to a natural watercourse to protect their property from flooding and protect their banks from erosion - may need to be modified to provide for effective river corridor planning.
PPS25

Planning policy statement 25 (PPS25) requires planning authorities and developers to:

• ensure flood risk is taken into account at all stages in the planning process
• avoid inappropriate development in areas at risk of flooding
• direct development away from high risk areas
• ensure that new developments take climate change into account and do not increase flood risk elsewhere.

The PPS25 practice guide highlights the importance of a hierarchical approach to surface water run-off and the flood risk implications. The four principles to follow are:

• assess – risks associated with surface water through regional, strategic and site-based flood risk assessments
• avoid – risks from surface water by controlling water at source through sustainable drainage systems (SUDS) and locating development away from risk areas
• substitute – apply the sequential approach to locate more vulnerable development in lowest risk areas
• control – use SUDS and implement surface water management plans to manage and reduce risk.

It is important to build in flexibility for future flood water storage at the regional or catchment scale and to provide strategic SUDS infrastructure into which attenuated flows can be discharged. Structural flood mitigation measures need to take into account strategic environmental impacts on the management of rivers. It is important to analyse the quality of existing infrastructure, assess the potential for river and floodplain restoration and to consider potential secondary uses for flood mitigation infrastructure such as ecological and amenity features including wetlands, lakes and ponds.

Understanding water catchment systems at sub-regional level is particularly important. Establishing a strategy for the short, medium and long term that addresses projected climates and scenarios can help steer related plans and policies. At this sub-regional scale, strategic flood risk assessments (SFRAs) form a basis for managing flood risk, and informing land use planning, and should be produced to inform strategies and plans at the city scale.

A number of local authorities have now prepared SFRAs, often jointly with neighbouring authorities as part of a sub-regional approach. An example is that of Northeast Yorkshire, where Ryedale District Council, Scarborough Borough Council, and North York Moors National Park Authority have jointly prepared a Strategic Flood Risk Assessment for their administrative areas (collectively known as Northeast Yorkshire). The SFRA makes recommendations for forward planning, as well as development control departments as well as indications for appropriate land management to ease flood risk. Another example of a good SFRA has been prepared by the Association of Greater Manchester Authorities.

At the sub-regional and smaller scales, non-structural flood mitigation measures can be explored. These do not involve physical barriers or diversions to flood water. At the coast, they involve a long-term, pragmatic approach to rising sea levels that results in areas being sacrificed to flooding though a process called ‘managed retreat’ of the coastline.

Within cities, potential measures include the extension of green infrastructure networks and the redesign of green spaces to allow for temporary flooding.

A decision to consider sacrificing land to flooding in the future is a challenging one to take. It requires the identification of appropriate land and robust assessments of the opportunities available. Decisions of this nature will most likely be taken at a regional level and be informed by catchment-scale plans. Preferred approaches should be explored and consulted upon through the relevant local planning processes to provide a robust framework for implementing a sustainable strategy to flood risk in a sub-region.

Photo by Stephen McLaren

Flood protection in Salford

More than 10,000 of Salford's properties are in a high-risk flood zone. In the 1990s Salford City Council and the Environment Agency started building the River Irwell flood control scheme and more recently the council completed the Salford strategic flood risk assessment (SFRA), which now influences planning decisions.

Read more about flood protection in Salford.

Priority: manage surface water and flood risk
Tags: water, regions and subregions