Dynamics of transmission losses in a large arid stream channel

The temporal dynamics of transmission losses are illustrated during single events within a 150 km long arid channel reach of the Kuiseb River, Namib Desert, Namibia. This is facilitated not using a traditional water balance study but by applying a mathematical flow routing scheme with parameters not calibrated with runoff information. Transmission losses are deliberately excluded from the model so that actual transmission losses can be identified as the component of model simulations that plots significantly higher than the measured discharges at the downstream end of the reach. Results indicate that transmission losses concentrate during high discharge peaks and are minor during small to medium flows. This behaviour is attributed mainly to enhanced water losses in flooded overbank areas. Although the exact percentage of groundwater recharge from these waters cannot be quantified, the present study implies that single high magnitude flows are more important than frequent small to medium flows for providing recharge and thereby sustaining the riparian vegetation of large desert streams.