A spatial information technology approach for the mapping and quantification of gully erosion

In contrast to the effort during the last decades to investigate sheet (interrill) and rill soil erosion processes, relatively few studies have been focused on quantifying and/or predicting gully erosion. The extension of the use of modem spatial information technologies, such as geographical information systems (GIS), digital elevation modelling (DEM) and remote sensing, have created new possibilities for research in this field. A key issue to be addressed, as the basis for predicting the effects of global changes such as land use and climate changes, is the mapping and quantification of gully erosion rates, including rate of retreat of gully walls and rate of sediment production. This research work presents a method to compute the rate of retreat of gully walls and the associated rate of sediment production caused by gully erosion. The proposed method uses multitemporal aerial photographs and multitemporal digital elevation models, both of which have been processed using GIS techniques. The research was applied to a sample catchment of 25 km(2) located in Catalonia, Spain. Aerial photographs at scale of 1:30,000 from 1957 and orthophotos from 1993 were used to map gully erosion and determine erosion rates between 1957 and 1993. The rates of channel incision and sediment production were computed from the subtraction of multitemporal digital elevation models. The rate of gully walls retreat was 0.2 m year(-1), representing a rate of 0.9parts per thousand m(2) year(-1). The maximum rate of channel incision (0.7-0.8 in year(-1)) occurred at the head of the gully and at meandering zones. The rate of sediment production caused by gully erosion was 1322 +/- 142 ton ha(-1) year(-1). In comparison with other methods to compute sediment production caused by gully erosion processes, the proposed method integrates the losses due to overland flow, mass movements and gully deepening and supposes an improvement to locate the areas within the gullies with higher erosional activity. (C) 2003 Elsevier Science B.V. All rights reserved.