SEPA national pluvial flood hazard mapping for Scotland

Location: Scotland (national scale project)                                                                 Client: SEPA

We have recently been commissioned by SEPA to complete the national pluvial flood hazard mapping for Scotland, with the project being split into 2 stages. Whilst the first stage of modelling and mapping methods is now complete, the second national rollout stage is now underway.

Challenge

To update the national pluvial flood mapping for Scotland and improve our understanding of surface water flood hazards, making the best use of the latest data, science and technology. Modelling will be undertaken across an area of over 80,000km2­ at 2m spatial resolution and requires over 34,000 simulations to be completed for draft mapping covering a wide range of return periods and multiple storm durations.

Solution

The project is split into two stages:

Pilot stage – Consisted of testing modelling and mapping methods, as well as a range of assumptions and parameters across four contrasting geographic locations within Scotland. This stage is now complete.

National rollout – The modelling and mapping of Scotland following the agreed approaches will be split into 11 geographical phases. This includes a wide range of return periods, multiple storm durations and the latest future drainage climate change scenarios. This stage is currently underway.

As part of the project, we have developed a new national composite Digital Terrain Model (DTM) at 2m spatial resolution, utilising over 20 sources of LiDAR and photogrammetry information supplied for the project. The new DTM includes the latest LiDAR coverage across Scotland providing a high-resolution representation of the ground topography, which improves the accuracy of predicted pluvial flood hazards.

Our in-house modelling software JFlow is being used to model and predict the surface water flood hazard for the whole of Scotland. JFlow solves the two-dimensional shallow water equations and is benchmarked against other established analytical solutions. The project is also trialling the use of emulation to supplement the potential approaches to producing surface water flood mapping.

Stakeholders will be invited by SEPA to provide feedback on draft pluvial mapping via a dedicated web review portal. Feedback will be reviewed and actioned to improve the final pluvial mapping product.

Benefit

The project will produce new national pluvial flood mapping utilising more recent design rainfall estimates and climate change guidance compared to the existing pluvial flood maps. The project will also utilise higher resolution elevation and land cover data to improve the accuracy of pluvial flood hazard mapping.

The updated mapping will have many forward uses, including informing future National Flood Risk Assessments and the management of surface water in future Flood Risk Management cycles. Other areas that the project outputs could feed into are surface water flood forecasting, natural flood management, adaptation programmes, property level protection and resilience, sustainable urban drainage systems, and blue-green infrastructure.

Want to know more?

For more information on this project, please contact Nicci Buckley or Iain Craigen.



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