A Planning Policy Statement 15 - Planning and Flood Risk (PPS15) and FLD1 - Development in Fluvial Flood Plains FRA in Northern Ireland.
About the project
Ambiental were approached to undertake a Planning Policy Statement 15 – Planning and Flood Risk (PPS15) and specifically FLD1- Development in Fluvial Flood Plains - compliant Flood Risk Assessment (FRA).
The development was positioned in Ballinamallard in Northern Ireland and was to build a Hydroelectric Scheme and Turbine House on a farm using the Killee Stream as the water source.
A little more about the project
Hydroelectric power harnesses the natural power of water using turbines that then move and as such generate electricity as the water passes between the blades. The position of the stream on the farm provided an ideal location for the hydroelectric power source, not only to provide extra income for the landowners but also a renewable energy source for the farm.
According to the Department of Agriculture and Rural Development – Northern Ireland (DARDNI) Rivers Agency, the proposed site was located within the present day and climate change predicted floodplains for rivers and surface water, meaning there was a risk of flooding. However, the nature of the development meant it had to be located within the stream and so was unavoidable. This meant it couldn’t be moved to a lower risk area.
The stream, referred to as Killee Stream, drains the surrounding 6km² area and was within 10m of the farm boundary. This allowed for sufficient water flow for the micro-scale hydro scheme, providing electricity for the farm as well as providing some income for the owners by selling the excess to the national grid.
DTM Image showing flood extents around the site boundary
The DARDNI Rivers Agency did not provide site specific flood data for the stream and therefore we had to use our UKFloodMap™ software data to model the potential flood levels at various fluvial extents.
UKFloodMap™ provides a detailed visualisation of potential flood risk and can cover 100% of the UK using remotely sourced topographic data where possible and manual recording of topography where this data is unavailable. It incorporates the most up-to-date river flow and rainfall data available from the Centre for Ecology and Hydrology (CEH). This covers a range of flood sources, including rivers, tidal, and surface water at a range of flood extends, including ranges of 30 to 1000 year return periods.
You find out more about how UKFloodMap™ works here: https://www.ambientalrisk.com/uk-floodmap4/
Given its proximity to the stream, the main source of the flood risk was found to be fluvial (river). However, there was also a risk of surface water flooding found on site.
The Ballinamallard River, which feeds the Killee Stream, was known to be used by migratory fish such as trout and salmon.
Using UKFloodMap™, it was found that the proposed development would have a negligible effect on the flood risk to the surrounding site.
It was also found that the construction of the turbine house was sufficient that even the 1:100 year flood scenario held a negligible risk to the turbine house and surrounding area, despite being a medium risk flood water height. This is due to the fact the development is designed to be water compatible and the displaced water would likely be on their own land which they were willing to sacrifice or create compensatory storage if required.