The objective of this paper was to analyse the consequences of land abandonment on erosion and to provide effective eco-engineering techniques for mitigation of gully erosion. The study was carried out in the Carcavo basin, a semi-arid catchment in Southeast Spain. At catchment scale all abandoned fields were surveyed and characteristics of each field, gullies and terrace failures were described. One abandoned valley was surveyed at a more detailed scale to create a precise DTM and detailed aerial photographs were taken to study vegetation patterns.
The results reveal that gullies on abandoned fields are often located on critical positions at the transition of the hillslope to the channel. This means that when a gully becomes active the connectivity of runoff and sediment in the landscape increases considerably, with the negative off-site effects as a consequence. A reconstruction of eroded sediment from the DTM confirms the importance of gully erosion in terms of sediment losses. Overflow at the lowest point and piping seem to be the main causes of terrace failure. Especially the influence of piping increases in dispersive soils after abandonment, because the topsoil is not ploughed anymore and runoff can enter directly the subsoil through cracks and macro-pores that have been developed after abandonment. Two potential soil and water conservation practices are: (1) Maintenance of terraces and earth dams, as a result more water is retained, which increases the vegetation cover and that strengthens the terrace or earth dam. Only in dispersive soils the risk of piping remains. (2) Revegetation on critical spots in the landscape with indigenous species that grow fast and have dense rooting systems to bind the soil.
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