Field techniques for estimating downstream changes in discharge of gravel-bedded ephemeral streams: a case study in southern Tunisia

Techniques for estimating discharge of gravel-bedded ephemeral streams, using only parameters measured from dry channels, are reviewed. For channels experiencing fluvial-type flows, the Darcy-Weisbach technique is appropriate. For channels experiencing debris flows, a technique based on flow tilt around bends can be applied. When used to estimate downstream changes in discharge of piedmont streams in the Tunisian Southern Atlas, the effects of transmission losses are clearly evident. Debris flow channels exhibit a more rapid loss of discharge, with flow confined to the proximal zone of the piedmont. These techniques provide a methodology of estimating discharge in uninstrumented ephemeral channels, where flow is unlikely to be encountered without a protracted period of monitoring.