Alleviating flood risk, facilitating economic growth, and helping revitalize an area steeped in rich history and natural beauty

River Deel Flood Relief Scheme

Flooding from the River Deel has long impacted Crossmolina Town. Events in 1989, 2006, and 2015 resulted in flooding of the three main streets in town, one of which is the N59 National Road. Mayo County Council requested the Office of Public Works (OPW) to carry out a feasibility study in 2012 on establishing a flood relief scheme for the River Deel. OPW then appointed our team to provide engineering and environmental services on all five stages of the project from Stage I (initial design and planning) to V (handover).

The purpose of the River Deel Flood Relief Scheme is to eliminate fluvial flooding in Crossmolina Town with a design standard of the 1% Annual Exceedance Probability (AEP) Event, more commonly known as a 1-in-100-year event. We’ve worked closely with OPW and other partners to design and implement the scheme.

Key elements include a river flow control structure, which will prevent flood water from reaching Crossmolina, as well as a new channel, which will divert those excess flood waters out of the River Deel and away from urban areas. We designed a new weir and spillway on the right bank of the river and at the upstream end of the new channel, two new road bridges at road crossing points along the route of the diversion channel, as well as a road diversion, which removes the need for further structures. The scheme also includes an energy dissipation structure, the creation of washlands between the downstream end of the new channel and the shore of Lough Conn, significant in-stream works, and careful modification of the natural hydrological regime in a sensitive environment (Natura 2000).

The scheme is currently under construction (Stage IV), and we are continuing to provide design support and project supervisor for the design process (PSDP) services to OPW.

In contrast with other schemes consisting of flood defenses alone, the River Deel Flood Relief Scheme will provide relief for even more severe events, as most of the excess water will be diverted over the new weir, straight to Lough Conn. The project will alleviate flood risk, facilitate economic growth, and will help revitalise an area steeped in rich history and natural beauty.