Impact assessment of drought mitigation measures in two adjacent Dutch basins using simulation modelling

The impact of two mitigation measures on groundwater and streamflow droughts in two lowland basins was investigated by applying the comprehensive transient model SIMGRO. Catchment behaviour was simulated with meteorological data from 27 yrs. Raising the water levels in the primary watercourses and raising the beds of the small watercourses was found to mitigate groundwater droughts. Surprisingly, the river discharges during low flow periods were also reduced, indicating that streamflow drought lasts longer and total discharge deficit increases. The simulation modelling also shows that urban expansion in two adjacent basins where all the storm water on the paved surfaces is directed to a sewage treatment plant in one of the basins mitigates the streamflow droughts there. However, if the storm water on the paved surfaces infiltrates into the ground within the city limits, the total drought duration and total discharge deficit increase. In the adjacent basin with no treatment plant, urban expansion combined with storm water infiltration mitigates the droughts.