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Flood risk assessment modelling in Scotland

By Douglas Swinbanks, Principal Flood Risk Consultant and Hydrologist at Aegaea

We recently caught up with Doug to discuss flood risk assessment modelling in Scotland… 

The Scottish Environment Protection Agency (SEPA) is an independent advisor on flood risk within the context of National Planning Policy. This includes a statutory role to provide flood risk advice for certain consultations. 


SEPA’s online flood maps are strategically designed and developed at a national scale to identify areas that are at risk of flooding. However, due to the broad scope of this methodology, particularly in rural areas, there may be a heightened level of uncertainty as crucial topographical details might be omitted, leading to potential inaccuracies. 

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


Further details outlining what information SEPA requires to be submitted as part of a Flood Risk Assessment and to outline methodologies that may be appropriate for design flow estimation (hydrological modelling) and hydraulic modelling are available within their ‘Technical Flood Risk Guidance for Stakeholders’ document. 

Picture of floods near the river Tay in Scotland

 At Aegaea, we have undertaken an extensive range of hydraulic modelling exercises and detailed flood risk assessments across Scotland. Our objective 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 numerous instances, our efforts have facilitated the liberation of developable areas previously categorised as being at risk. 

Flood Modeller is our go-to hydraulic modelling package for detailed Flood Risk Assessments and is a robust platform to accurately simulate 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 also allows us to undertake 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 use Flood Modeller here at Aegaea extensively across multiple projects. Not just because it's an industry-leading 1D solver, but it provides the flexibility of 1D and 2D modelling to capture critical flowpaths.  With its easy integration with Wallingford HydroSolutions WINFAP and ReFH2 software – Flood Modeller is an essential tool when assessing fluvial flood risk in Scotland. 

Picture of Douglas Swinbanks and Aegaea logo

Doug Swinbanks Principal Flood Risk Consultant and Hydrologist 

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.  


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