An Evaluation of Two Ten-Year Sediment Budgets, Nahal Yael, Israel

The method used to derive a crude ten-year sediment budget for Nahal Yael—a small hyper-arid catchment in the Southern Negev Desert—is applied to a later ten-year period, for which a much more accurate sediment budget is available. Results indicate that the budget of the first decade has overestimated the suspended sediment output by a factor of four, and underestimated the bed material output by a factor of two. Evaluated against the background of similar sediment budget studies, it is concluded that the main source of potential errors in sediment budgets, especially in those involving considerable amounts of bed material, lies not so much in the volumetric before-after comparisons, based on surveying. Rather, errors are caused mainly by the inadequate procedures presently available for the estimation of sediment input into, and output from, the studied reach.