Langholm Flood Risk Assessment
Dumfries and Galloway Council
RPS was appointed by Dumfries and Galloway Council to undertake a flood risk assessment of the river and its tributaries and develop a range of flood risk management solutions.
Langholm is located along the River Esk at the confluence of two of its tributaries and has flooded historically.
RPS specified and procured a detailed topographical survey of the river channel and utilised LiDAR data to define the floodplain. A detailed hydrological analysis was undertaken using local gaugings and FEH analysis and a hydrodynamic model was created in InfoWorks ICM using a fully integrated 1D in bank 2D out of bank flood model. The model was used to provide flood extents for a wide range of flood events including 50%, 20%, 10%, 5%, 2%, 1%, 0.5% and 0.5% AEP + Climate Change events.
RPS subsequently developed a range of measures which addressed the flood risk to the town from the 0.5% AEP + climate change events. These measures, which included a series of earth embankments, reinforced concrete walls and demountable defences, were then costed. A full cost benefit analysis was undertaken in accordance with the requirements of the Multi Coloured Manual from the University of Middlesex and the SEPA document "Flood Protection Schemes – Guidance for Local Authorities".