Soil denudation in the northwestern Negev (Israel) following the Late Byzantine – Early Islamic period

Abstract

During the 5th and 6th centuries, the economic hinterland of the city of Gaza encompassed a network of settlements that supplied the city with agricultural produce. Water was collected in underground cisterns from rooftops and courtyards. While almost nothing remained of the above-ground structures since the settlements collapsed, soil erosion exposed these cisterns, which now serve as well-preserved indicators of the location and levels of the houses - that supplied the water. The study examines to what extent the land abandonment in the late Byzantine - early Islamic period resulted in denudation and soil property changes. We hypothesize that the abandonment of settlements and agriculture intensified soil erosion and amplified gully development. Approximately 140 cisterns were mapped in the study area, mainly north of the ephemeral Nahal Gerar stream. The height of the cisterns above the ground was used to calculate the denudation rate (DR) since abandonment. Findings indicate that over relatively flat terrains (1–5 %), cisterns protrude 0.5–1.2 m above the surface. Considering abandonment in the 6th or 11th century, DR was calculated as 0.35–0.85 mm/yr or 0.5–1.2 mm/yr, respectively. Over steeper slopes (10–12 %), along river banks and incised gullies, extensive bank erosion occurred, leading to the exposure of cisterns up to 2.5 m; DR = 1.8 to 2.5 mm/yr, depending on the abandonment time. The settlements' distribution and the surface topography directly correlate: in settled areas, Terrain Roughness Index (TRI) values are higher compared to other areas with the same lithology and rainfall amount. Following abandonment, decaying houses resulted in the complete disintegration of mud bricks, increasing the proportion of fine soil fractions. Cisterns acted as sedimentation basins, trapping surface-derived sediments and debris, including degraded brick material. This process influenced the mechanical composition of soils, affecting soil erosion and land degradation.