Jonathan B. Laronne
Department of Geography & Environmental Development, Ben Gurion University of the Negev, Israel

This contribution emphasizes new developments in sediment transport with respect to applications in semiarid and arid rivers. Bedload fluxes are several orders of magnitude higher in ephemeral channels than in humid complements due to an almost endless supply of bed material. Bedload discharge datatasets follow the Meyer Peter and the recent Parker equations rather well, demonstrating the high efficiency of ephemerals. The suspended sediment fraction makes up for most of the sediment, decreasing with increased aridity from 90 to about 50 percent. Suspended sediment dynamics are considerably simpler than in humid areas, with superior predictive power to assess sediment yield.

Surface water reservoir objectives, design and operation are different in arid areas. They are based on water supply indeterminacy, accelerated water losses and very high suspended sediment loads leading to short life spans. High rates of sedimentation are particularly offensive. A novel stratigraphic approach allows the immediate determination of historic sedimentation rates and even to resolve the probability distribution function of event sediment yields. Recent studies and designs have demonstrated a variety of means to increase the economic feasibility of reservoirs in arid areas. These include backup water supply systems, more efficient use of water via multiple operation, design of low sedimentation reservoirs and the industrial reuse of reservoir sediments leading to reservoir rejuvenation.