GEOMORPHOLOGICAL SURVEY AND GIS TECHNIQUES AS A TOOL FOR PREDICTIVE EROSION MAPPING

Ojeda Guillermo

Universidad Nacional de San Luis, Chacabuco y Pedernera, San Luis 5700 Argentina. e-mail: ojeda@unsl.edu.ar

In semiarid central-western Argentina, rainfall are enough to produce runoff, but still scarce to generate a protective vegetationl cover. Fifteen percent of the country is prone to erosion by water and this affects specially the scarce productive areas of this region. Erosion is principally significative nearby the border of the San Luis range and it is developed in loess cover overlying a Tertiary paleo-landscape gently undulated. The southeastern range margin is characterized by a high-density of gullies, some of them forming ravines and hence disabling many areas for agricultural laboring. Detailed geomorphological cartography is being developed with the aim of determining the type, degree, evolution and distribution of erosional activity. Working methodology includes the definition of cartographic units through to ITC System of geomorphological survey, where the major units are delimitated considering morfogenetic issues. These units were determined based on aerial photos and TM imagery with scales ranging from 1:20,000 to 1:100,000. Other variables such as lithology, climate, soils, topography, vegetation and land use have been considered in order to evaluate the erosion phenomena. This information has been organized in a database, with the aim of employing GIS capabilities. By overlaying GIS cartographics functions, geomorphological units were related with gully distribution and enviromental data in order to recognize the degree of coincidence among them. This procedure is a first approach for achieving empirical rules which can lead to build predictive models.