Production of a GIS Based SIMCAT Model for the South West River Basin District in Ireland

WRc has recently completed a SIMCAT pilot study for the South Western River Basin District (SWRBD) in Ireland. The Environment Agency, in England and Wales, has developed its SIMCAT water quality modelling tool, with assistance from WRc,  to support decision making for river water quality management and the development of Water Framework Directive River Basin Management Plans.

The overall aim of the study in Ireland was to evaluate SIMCAT as a suitable water quality modelling tool to support the development of River Basin Management Plans. The main objectives of the study were:

1. To use catchment data and geographical information available in the SWRBD to produce and calibrate a SIMCAT model;
2. To use the model to assess predicted current water quality against WFD standards and demonstrate the impact of planned improvements to effluent discharges;
3. To assess the impact of a specified climate change scenario on water quality; and,
4. To provide training in the use of the model.

 A single SIMCAT model was developed to represent river flow, BOD, DO, Ammonium, Nitrate and Phosphate. The model included:

• 1172 river reaches;
• 600 headwaters;
• 69 flow gauges;
• 438 river quality monitoring sites,
• 68 abstractions;
• 105 current, plus 36 additional, future wastewater treatment plant discharges; and,
• 37 IPPC industrial discharges.

The model was built and calibrated using WRc’s SIMCAT model development protocols. Model scenario results for predicted river quality were assessed against standards identified by the SWRBD. The current scenario results identified that 148 river quality monitoring sites out of a total of 438 would fail for one or more parameters. The largest number of failures was due to Phosphate (36%) and Ammonium (30%). The future scenario, incorporating projected growth and the application of Urban Waste Water Treatment Directive emission standards at qualifying discharges, produced similar results to the current scenario. The climate change scenario was applied to the River Bandon catchment based on projected changes to river flows. The effect was to increase winter flows and decrease summer flows but the mean flow was unchanged. The water quality impact, using the future scenario, resulted in a slight deterioration in water quality towards the bottom of the catchment.

The study demonstrated that SIMCAT models can be produced from available routine monitoring data in Ireland and can be used to support River Basin Management Planning.