Flood Storage Scheme

The Wemyss and March Estate is one of 7 riparian owners of St Mary’s Loch and was party to the innovative and sustainable approach to reducing flood risk to the Yarrow catchment which includes the town of Selkirk. Flooding within this catchment is a regular and often devastating event, resulting in significant financial and economic loss to individuals and businesses alike.

The St Mary’s Flood Storage Option was designed as part of the wider Selkirk Flood Protection Plan and delivers multiple benefits by utilising the natural ability of the Loch to store water during a flood event. An intelligent water management system which responds to weather forecast and modelling data, allows the water levels on the Loch to be managed according to season and weather forecasts. The water level in the loch was lowered by 650mm from previous levels and the spill way was increased in height by 250mm – in combination this provides an additional 900 mm of additional freeboard, creating extra storage capacity when required of around 3 million cubic meters of water, water that otherwise would flow down the river system during a flood event. Peak flow rates have been reduced by up to 20% during a flood event as a result of this project.

From the Estate’s perspective, this project neatly aligns with others being undertaken by the Estate, such as the Little Yarrow Scheme and our Peatland restoration program, both of which help to manage and reduce water flow rates from the uplands.

In combination, this is a fine example of a joined up approach to deliver a natural solution to reduce flooding risk and highlights the multiple benefits that can be achieved from sound biodiversity planning and implementation.