SEPA National Flood Risk Assessment

RPS were commissioned by the Scottish Environmental Protection Agency (SEPA) to develop an automated GIS analysis tool for use in the 2018 National Flood Risk Assessment (NFRA2). The Flood Risk Management (Scotland) Act 2009 (FRM Act) requires SEPA to prepare a flood risk assessment for each flood risk management district.

Challenge

In December 2011 SEPA produced a National Flood Risk Assessment (NFRA) for Scotland which provided a high level screening tool which assessed the relative adverse consequences of flooding across the country. The purpose of the NFRA is to identify locations where a significant flood risk exists, or is likely to occur in the future, by assessing the potential adverse consequences of any future flood, and the impacts of significant historic flood events, to human health, the environment, cultural heritage and economic activity. The overall purpose of the NFRA 2 (and subsequent cycles) is to continually improve the understanding of flood hazard and risk across Scotland and prime further development in flood maps and strategies.

Solution

RPS developed an automated approach in close consultation with SEPA that can take in all flood hazard data for Scotland and produce individual receptor risk information for all 2.5 million Residential Properties, 0.5 million Non-Residential Properties, 40,000 Community Facilities, 8,000 Utilities, 840,000 Road segments and over 1 million Agricultural land parcels in Scotland, as well as all national environmental sites, cultural heritage sites, airports and railway lines in the country.

Fluvial, coastal and pluvial flood depths, velocities and extents were used for all scenarios (10yr, 25/30yr, 50yr, 100yr, 200yr, 1000yr, 30yrCC, 200yrCC) to assess individual and combined flood risk and calculate damages for all receptors. A conceptual model workflow was designed and models were initially built in ArcGIS model builder. These models were then converted and refined into a set of complex modular Python scripts capable of carrying out the NFRA2 methodology on a national scale and producing the required grid-based outputs which provide a visual pattern of flood risk across Scotland.

RPS carried out the initial national runs of the data and by taking a collaborative approach to the model development with SEPA and continually making minor amendments to various modules within the package. The final product that is delivered to SEPA is made up of 3 main modules, 1. Pre-processing hazard and receptor data, 2. Receptor Analysis, and 3. Grid Outputs. The continual improvement and refinement of the automated workflow has enabled very fast runtimes, along with a great amount of functionality to be built into the models, to allow SEPA to update information and parameters based on best practice and best available scientific information. 

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