TOBIN Consulting Engineers, in association with Royal Haskoning, were commissioned by the OPW to undertake a Flood Study of the Dunkellin River and Aggard Stream in March 2010.
A Hydraulic Model was produced for the 11km reach of the Dunkellin River and associated reaches of the Aggard Stream, using ISIS river modelling software. The Hydraulic Model was used to develop a suite of Flood Alleviation Measures, which could successfully accommodate a flood of the magnitude of that experienced in November 2009, under the specific constraints encountered within the study area. A costed package of Flood Alleviation Works along the Dunkellin River, and the Aggard Stream, was produced which could accommodate the 100 Year Flood, with an allowance for climate change. The initial study was completed, on schedule, in a three-month period to June 2010, culminating in the submission of the final report, “Study to Identify Practical Measures to Address Flooding on the Dunkellin River including the Aggard Stream”.
TOBIN were subsequently commissioned by Galway County Council (GCC) to provide Engineering Consultancy Services for the detailed design stage of the “Dunkellin River and Aggard Stream Flood Relief Scheme”. The initial Flood Study, and subsequent detailed design process, recognized a number of critical constraints, which exist around the development of a successful Flood Relief Scheme along the Dunkellin drainage network. The “Viable Scheme” has avoided impacting adversely on the existing Hydrology and Ecology of the Rahasane Turlough, through avoiding channel works within the turlough and also ensuring that Flood Alleviation Works proposed upstream and downstream do not significantly alter the turlough’s hydrology during normal hydrological conditions. This has been predominantly achieved through a two-stage channel design with outflow from the Rahasane remaining unaffected during normal river flows. A stepped channel provides an increased outflow capacity during more extreme flood conditions.
The Dunkellin River also discharges to shellfish waters in the inner Galway Bay. These waters are particularly sensitive, due to the risk of increased shellfish mortality which can occur from local reductions in salinity at the estuarial discharge location. TOBIN is currently working closely with the Environmental Consultants for the Dunkellin River Study, to ensure that the final Flood Relief Scheme adequately addresses all of the constraints, which have been identified throughout the consultation and design process. The public consultation process has been a particularly important aspect of the Dunkellin River Study; not only in increasing public awareness and acceptance of the final scheme, but also in identifying the complex issues which exist within the study area at an early stage of the process. This has resulted in these constraints informing the development of Flood Risk Management solutions at an early stage, thus increasing the overall efficiency of the design process.