Implementation of the Flood Risk Management (Scotland) Act 2009: report to the Scottish Parliament - 2019

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 sections of the drainage system can work in unison 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

Great progress has been made since the introduction of the Flood Risk Management (Scotland) Act 2009 in understanding the impact of surface water flooding in Scotland, where our priorities lie and how we can work together to manage the impacts of floods on our communities.

In 2015 the first FRM Strategies set out a clear framework for the management of surface water flood risk requiring 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 found that surface water flooding accounts for 23% of annual flood damages in Scotland. The Strategies also identified 113 towns and cities that require a surface water management plan (SWMP). SEPA, Scottish Water (and other responsible authorities) are working in partnership with local authorities to support the production of the SWMP's.

The second National Flood Risk Assessment was completed in 2018 using improved surface water modelling and mapping techniques. It identifies approximately 210,000 homes, businesses and services at risk from surface water and estimates that this will increase to 270,000 by 2080 through climate change.

Recognising the size and complexity of this challenge and the call from the Scottish Advisory and Implementation Forum for Flooding (SAIFF) for "a transformation in the way we handle surface water", Scottish Government's Programme for Government 2019-20 makes commitments to work together to increase Scotland's use of blue-green infrastructure for drainage and flood management and to review our approach to blue-green cities and bring forward proposals by the end of 2020.

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 and surface water sewers for example. They 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.

In 2019, five of these studies have progressed to the Optioneering phase of work, which will identify the most sustainable solutions for managing flood risk in areas that have been identified as joint priority needs areas for Scottish Water and the local authorities. The Optioneering phase is due for completion during FRM cycle 1.

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. Six of these twelve studies have completed this stage in 2019, with the final six due for completion in 2020. Dependent on the outcomes of this phase of the studies, it is possible that some of these areas will continue to an Optioneering phase.

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 assess flood risk from the sewers systems across 201 catchments by the end of the first FRM cycle. As of December 2019, 177 assessments have been completed. All other Section 16 assessments are on programme for completion within the first FRM cycle. On completion, the outputs are provided to SEPA for use in the NFRA2 and the continued development of their pluvial mapping. The outputs are also provided to the appropriate local authorities as part of their Surface Water Management Planning Process.

4.5 A Place-based Approach to Surface Water Management

Our urban areas in particular face mounting challenges with surface water drainage and related flooding. Despite considerable capital investment, the continued densification of our towns and cities is adding to the pressure on drainage systems that are already at capacity and the "total asset" that needs to be flood resilient continues to increase.

Overcoming this by taking an integrated place-based approach focused on blue-green infrastructure has the potential to deliver multiple benefits for our communities. The long established Metropolitan Glasgow Strategic Drainage Partnership has demonstrated the many advantages of this approach.

2019 saw the establishment of the Edinburgh and Lothians Strategic Drainage Partnership which seeks to ensure that the area's prosperity is enhanced by taking a holistic approach to water management and climate adaptation.

In the Aberdeen area the Sustainable Growth Agreement between SEPA and Scottish Water is working with Aberdeen City Council to drive innovation in managing rainwater and waste water drainage. These innovations aim to significantly reduce flows to the combined sewer, increase resilience and contribute to place.