SPATIAL AND TEMPORAL VARIABILITY OF WATER PERCOLATION AND MOVEMENT IN A SYSTEM OF LONGITUDINAL DUNES,WESTERN NEGEV,ISRAEL

Subsurface lateral flow has previously been identified in dune areas where the average annual rainfall exceeds 200 mm. Very little is known about subsurface flow in sandy deserts with less than 100 mm of rainfall per year. The present study deals with the water regime in a system of longitudinal dunes in the Negev desert. Sixteen boreholes were dug, down to a depth of 6 m, across a sandy ridge and the adjacent corridor. Soil moisture and water movement were monitored with a neutron probe during two consecutive years. The first year had been relatively wet and in the following year the rainfall was slightly lower than the long-term average. The data obtained show that in an average year water percolation is limited to 60 cm with no lateral water movement. Deeper percolation, in the range 180–400 cm, occurs in response to rainy spells with about 100 mm of cumulative rain within two months. The process involves subsurface lateral flow and water movement by the piston effect. The lateral flow, on the flanks of the dune, is explained by differences in hydraulic conductivities within the sloping layers. © 1997 by John Wiley & Sons, Ltd.