Runoff from loess or bedrock? Hillslope geoarchaeology of ancient runoff farming systems at Horvat Haluqim and Har Eldad in the central Negev Desert

Remains of ancient farming systems based on runoff harvesting are widespread in the central Negev Desert. Modern hydrological research in the region led to two alternative concepts in relation to runoff generation, one placing the emphasis on loess and the other on bedrock. Did the ancient inhabitants design their farming systems to obtain runoff from loess-covered surfaces or rather from bedrock outcrops?Reconstruction of each ancient runoff-farming site with multi-annual hydrological measurements to answer the above question is obviously impossible. Yet, the focus of archaeology is site specific and requires individual research at each location. Therefore, we developed a geoarchaeological approach that can be used at each site to address the above question and assess the relationships between archaeological runoff-farming remains and related geomorphic hillslope features.We tested our approach at two different sites: (1) Horvat Haluqim on the Haluqim Anticline; (2) Har Eldad in the Avdat area. The concave hillslopes at Horvat Haluqim are 45-85 m long, becoming steeper (20-30°) towards the first-order terraced wadi-bed. Colluvium is generally absent. Bedded limestone outcrops (17-57%) alternate with patches of loess and stones (43-83%) along the entire hillslope. Human-made conduits and stone mounds do not exist here. Hence, runoff from the natural catchment-alternating bedrock and shallow loess-supplied the terraced fields with water.At Har Eldad, ancient long-range runoff channels begin on the extensive flat (3% gradient) hilltop plateau, (ca. 50 ha) covered with loess and stones (98%). The steep upper slope (130 m) is dominated by limestone bedrock (ca. 90%). The very long (224 m) convex colluvial slope (99.9% loess and stones) exhibits stone mounds, stone strips, and conduits. Runoff was obtained both from loess and bedrock surfaces to supply water to terraced wadis below Har Eldad.Both sites indicate that the loess runoff theory and bedrock runoff theory are complementary and not contradictory.