Implementation of the Flood Risk Management (Scotland) Act 2009: report to the Scottish Parliament

4. Surface Water Management

4.1 Background

Urbanisation has altered the natural drainage process. Rain falls everywhere so all features of our urban landscape, by design or otherwise, influence surface water run-off and flooding. Surface water flooding is often a complex interaction of many sources of flooding, including flooding from piped systems when their capacity is exceeded, small urban watercourses and direct inundation from surface water run-off.

It is widely recognised that sustainable surface water management ensures that above and below ground parts of the drainage system can work in concert to deliver benefits for flood risk management, people, the water environment and biodiversity, while also making our urban areas more adaptable to future changes and more resilient to climate change.

4.2 Surface Water Management

The Flood Risk Management (Scotland) Act 2009 has driven significant improvement in the understanding of surface water flood risk and management of surface water flooding in Scotland.

The first National Flood Risk Assessment in 2011 (NFRA) was the first time national maps of surface water flood hazard and risk were available for Scotland.

In 2015 the first FRM Strategies set out a clear framework for the management of surface water flood risk; they require local authorities to lead on the development and implementation of surface water management plans in those areas with the greatest risk of surface water flooding.

The FRM Strategies identified 113 towns and cities that require a surface water management plan (SWMP).

The Strategies found that surface water flooding accounts for 23% of annual flood damages in Scotland.

SEPA, Scottish Water (and other responsible authorities) are working in partnership with local authorities to support the production of the SWMP's.

4.3 Integrated Catchment Studies

Scottish Water is leading on a number of Integrated Catchment Studies in partnership with 20 local authorities across Scotland. These studies aim to create a detailed understanding of the above and below ground drainage systems – combined sewer network, culverted and open watercourses, surface water sewers for example. The aim to understand the interactions of the drainage network and identify the sources and mechanisms of flooding in these urban areas. These studies were commissioned in two batches and are currently at varying stages of development.

Five of these studies will begin the Optioneering phase of work in early 2019 which will identify the most sustainable solutions for managing flood risk in areas which have been identified as joint priority needs areas for Scottish Water and the local authorities.

Twelve studies are continuing through the model build and verification stages. These will then be taken forward to undertake a catchment flooding assessment which will identify the sources, mechanisms and impacts of flooding. It is expected that a number of these studies will continue to the Optioneering phase when these stages have been completed.

4.4 Section 16 Assessment of Flood Risk from the Sewer Systems

Scottish Water is progressing on schedule with the program to undertake modelling to assessment of flood risk from the sewers systems across 201 catchments by the end of the first FRM cycle (2021). As of December 2018, 97 assessments have been completed. All other S16 assessments are on programme for completion within the FRM cycle. On completion the outputs are provided to SEPA for use in the NFRA2 and continued development of the pluvial mapping and the appropriate local authorities as part of their Surface Water Management Planning Process.

4.5 Programme for Government Commitments

The Programme for Government 2018/19 makes a specific commitment in relation to surface water management. It highlights the need for cooperation to develop approaches to drainage which will

• reduce the burden on the sewerage network
• reduce the need for costly new infrastructure
• reduce flood risk.

It sets out the ambition to take steps to join the international trend towards Blue-Green cities, which will have multiple benefits for the environment and leisure and outdoors activity.