VERY HIGH-RATES OF BEDLOAD SEDIMENT TRANSPORT BY EPHEMERAL DESERT RIVERS

GEOMORPHOLOGISTS have thought for some time that rates of sediment tra nsfer might differ markedly in ephemeral and perennial rivers, and hav e used this idea to explain both the changing character of sedimentary successions and the morphology of rivers in sub-humid or semi-arid ar eas that have experienced significant shifts in climate during the Qua ternary period1-5. But until now there has been a lack of suitable fie ld data to confirm this suggestion, mainly because floods in arid zone s are infrequent and unpredictable. Here we present bedload sediment t ransport data for an ephemeral river in Israel, which show it to be, o n average, as much as 400 times more efficient at transporting coarse material than its perennial counterparts in humid zones. This suggests that existing predictive sediment transport equations24, developed an d calibrated exclusively with data obtained in perennial rivers, are i nadequate for application to rivers in arid environments. It also sugg ests that areas that are at risk of shifting from sub-humid to semi-ar id conditions as a result of prospective global changes in climate may suffer severe sedimentation problems.