Soil moisture variability in a semi-arid gully catchment: implications for runoff and erosion control

Spatial patterns in surface soil moisture during dry and wet weather conditions have been recorded over a 3.68 ha gully catchment in central Spain. During dry weather conditions this spatial pattern was characterised by areas of relatively wet and dry soil, forming a mosaic of areas with contrasting hydrological response. Semi-variogram analysis has indicated that these areas are spatially isolated and unconnected, with the effect that surface runoff from source areas within the catchment may be re-absorbed by surrounding areas which act as sinks for overland flow. Consequently during dry weather conditions, variation in the soil's physical and hydrological properties, as reflected by spatial differences in soil moisture, may be advantageous in minimising widespread catchment runoff and erosion, by creating spatial isolation of runoff producing areas and by promoting discontinuity in hydrological pathways. During wet weather conditions, however, extensive saturation, exceeding a catchment wetness threshold, increased spatial continuity in hydrological pathways, regardless of the spatial variation in soil hydraulic properties, resulting in widespread runoff and erosion. Management strategies should therefore aim to raise this wetness threshold value, by improving the soil; physical and hydrological properties. The creation of a mosaic pattern of areas with contrasting hydrological response may prove to be an effective management strategy in runoff and erosion control in semi-arid environments. (C) 1998 Elsevier Science B.V.