Water harvesting by ancient farmers in the Negev desert, Israel: Overland flow generation and continuity considerations

Stone mounds and water conduits dating from the Nabatean, Roman and Byzantine periods (4^th century B.C. to 7^th century A.D.) can be found on hillslopes over large areas in the Negev Desert, as well as in other parts of the Middle East and North Africa.

Based on results from field and laboratory experiments it is suggested that the ancient farmers were very efficient in harvesting water; they took into consideration the size and position of the stones when clearing the hillslope surface in order to increase the overland flow yield.

A comparison of the volume of stones in the mounds to the volume of surface stones from the surrounding areas indicates that the ancient farmers removed only stones that had been rested on top of the soil surface and left the embedded stones untouched. According to the results of simulated rainfall experiments, this selective removal of stones increased the volume of overland flow generation by almost 250%, for small rainfall events, compared to natural untreated soil surfaces. In addition, they realized that installing closely spaced conduits running in parallel along the hillslope would increase the trapping efficiency of overland flow on its way downslope.

This means that the ancient farmers have been well aware of the mechanisms of overland flow generation on stony soils and of overland flow dis-continuity on arid hillslopes.