Utilization of hydrodynamic modelling to quantify water losses from the Sundays River between Darlington Dam and Korhaans Drift Weir

This study quantified transfer losses over the 2021/2022 water year for irrigation releases from Darlington Dam into the Sundays River, which are diverted at the Korhaans Drift Weir.  A one-dimensional (1D) hydrodynamic model was set up and calibrated to simulate the transfer losses which were assumed to consist primarily of evaporation and evapotranspiration (ET). Flow measurements were undertaken with an acoustic doppler current profiler (ADCP) to verify the calibrations of the Parshall flumes at Darlington Dam and at Korhaans Drift Weir.  The ADCP results showed that the Department of Water and Sanitation’s (DWS’s) existing discharge tables underestimated lower flows by 13% and higher flows by 16%.  The hydrodynamic model results also estimated transfer losses between Darlington Dam and Korhaans Drift to range between 2.0% and 5.3%.  It was determined that the transfer losses were seasonal and were lower than those determined by similar studies for other South African rivers.