Sediment yields in hyper-arid areas of the Middle East exemplified by Nahal Nehushtan, Israel Dr. Rachel Armoza-Zvuloni Dead Sea and Arava Science Center, Israel

Floods rarely occur in hyper-arid deserts and little is known about the magnitude and frequency of sediment delivery from their basins, despite their importance to changes to the landscape as well as to infrastructures and engineering activities. Sediment yield from the Nahal Nehushtan watershed (15.7 km2) located in the Timna Valley in southern Israel, was determined by assessing stratigraphic sections in its 60-year reservoir deposits.

Stratigraphic correlation between event couplets allowed quantification of sediment yields representing 13 former flash-flood events. Based on the sediment volume in the reservoir, the 24.6 t km-2 y-1 average sediment yield is very low by global standards, slightly less than that of the nearby Nahal Hiyyon, though the latter's drains an area larger by almost two orders of magnitude. Among the event layers, five are voluminously small and seven are medium-sized. The thickest layer, deposited by a flash flood caused by a single rain event, contributed 29% of the total sediment yield. This demonstrates the overarching effect of medium magnitude events on the rate of sediment production in a hyper-arid environment. Based event reservoir sedimentation from watersheds located in several hyper-arid areas in the Middle East, sediment load increases with drainage area as expected. However, the variation of mean annual sediment yield with flood frequency is variable, considerably depending on local characteristics. Our quantitative results together with previous studies of hyper-arid areas, provide complementary evidence of fluvial sediment transport - the main landscape designer in deserts.