Runoff-induced sediment yield over dune slopes in the Negev Desert. 1: Quantity and variability

Although extensive data exist on runoff erosion and rates for non-sandy hil lslopes, data for arid dune slopes are scarce, owing to the widespread perc eption that the high infiltrability of sand will reduce runoff. However, ru noff is generated on sandy dunes in the Hallamish dune field, western Negev Desert, Israel(P approximate to 95 mm) due to the presence of a thin (usua lly 1-3 mm) microbiotic crust. The runoff in turn produces erosion. Sediment yield was measured on ten plots(140-1640 m(2)) on the north- and s outh-facing slopes of longitudinal dunes. Two plots facing north and two fa cing south were subdivided into three subplots. The subplots represented th e crest of the active dune devoid of crust, the extensively crusted footslo pe of the dune, and the midslope section characterized by a patchy crust. T he remaining plots extended the full length of the dune slope. No runoff and consequently no water-eroded sediments were obtained from the crest subplots devoid of crust. However, runoff and sediment were obtained from the mid- and footslope crusted subplots. Sediment yield from the foot slope subplots was much higher than from the midslopes, despite the higher sediment concentration that characterized the midslope subplots. The mean annual sediment yield at the Hallamish dune field was 432 g per me tre width and was associated with high average annual concentrations of 32 g l(-1). The data indicate that owing to the presence of a thin microbiotic crust, runoff and water erosion may occur even within arid sandy dune fiel ds. Copyright (C) 2001 John Wiley & Sons, Ltd.