Variability of gully erosion in a small catchment in South-west Spain

Abstract

Research on gully erosion is carried out as part of an investigation on erosional and hydrological processes in a small catchment in Extremadura, Spain. The amount of gully erosion is estimated by repeated monitonng of transverse sections since summer 1990. Data obtained so far indicate high spatial and temporal variability. High amounts of erosion are related to a channel section with active headcut retreat, whereas net accumulation occurs where the gully is already deep and wide. Present erosion, apart from headcut retreat, is related to lateral undercutting of the channel bank and bank collapsing. Temporal variability is related with rainfall characteristics and discharge production in the channel. Important sediment losses are produced by highly intensive storms. The most important gully process in the area is shown to be related with the erosive force of flowing surface waters. Furthermore it is discussed whether present active erosion is related to abandonment of cereal cultivation in parts of the catchment about 30 years ago. It is thought that reduced soil erosion on hillslopes due to the change in landuse, and hence lower sediment supply to the channel in the last decades increased gullying.