Flood Risk Assessment Modelling in Scotland

Douglas Swinbanks, Principal Flood Risk Consultant and Hydrologist at Aegaea

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Introduction

The Scottish Environment Protection Agency (SEPA) plays a vital role as an independent advisor on flood risk within the framework of National Planning Policy, including a statutory role to provide expert flood risk advice for specific consultations.

National Scale Flood Maps

SEPA’s online flood maps are meticulously designed and developed at a national scale to identify areas at risk of flooding. While this broad methodology is highly effective, particularly in rural areas, there may be some level of uncertainty as certain topographical details might be omitted. This is where hydraulic modelling comes into play.

To gain a more precise understanding of flood risk for your development site, hydraulic modelling is essential. This approach allows for the accurate determination of the Flood Risk Area (the 1 in 200 year plus climate change extent) and assesses the available developable area with greater precision.

For more detailed information on what SEPA requires to be submitted as part of a Flood Risk Assessment, as well as appropriate methodologies for design flow estimation (hydrological modelling) and hydraulic modelling, please refer to their ‘Technical Flood Risk Guidance for Stakeholders’ document.

Unlocking Developable Areas

At Aegaea, we have conducted an extensive range of hydraulic modelling exercises and detailed flood risk assessments across Scotland. Our goal has been to enhance SEPA’s projections by refining them at a site-specific level, thereby providing a more precise assessment of flood risk.

In many instances, our efforts have successfully unlocked developable areas previously categorised as being at risk.

Flood Modeller is our preferred hydraulic modelling package for detailed Flood Risk Assessments. It is a robust platform that accurately simulates peak water levels for both large and small watercourses across the country. This enables us to determine the Flood Risk Area and evaluate potential impacts on future development sites with greater precision.

Additionally, Flood Modeller allows us to perform the additional simulations often requested by SEPA and/or the Local Authority, including structure blockage assessments (regularly up to 75% opening reduction) and joint probability analysis. These additional simulations are becoming more prominent since the release of the National Planning Framework 4 (NPF4).

We extensively use Flood Modeller across multiple projects. Not only is it an industry-leading 1D solver, but it also provides the flexibility of 1D and 2D modelling to capture critical flow paths. With its seamless integration with Wallingford HydroSolutions' WINFAP and ReFH2 software, Flood Modeller is an essential tool for assessing fluvial flood risk in Scotland.

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Doug Swinbanks

Doug is a Principal Flood Risk Engineer and Hydrologist based in Edinburgh. He has been involved in both small- and large-scale developments – including delivering flood risk assessments, detailed surface water management plans, river restoration studies and flood defence schemes. His work included the Oban Flood Risk Management Study in Argyll and Bute as well as the detailed design and delivery of the surface water/SuDS drainage system for the 3000+ home development near Stirling, which at the time was the largest development to be approved in Scotland in a single sitting.