LAND-USE PLANNING: ELABORATION OF THE HIDRIC EROSION HAZARD MAP AND APLICATION OF MORPHOMETRICAL PARAMETERS

Abstract

The studied area is about 105.803 hectares and comprises the Auca Mahuida Protected Natural Reserve.
It is located in the east-northeast of Neuquén Province, Argentina. Population density ranges between
0.4 and 0.7 inhabitants per square kilometre and meteorological and hydrogeological data are absent The
surface geology comprises Neogene volcanic rocks overlaying subhorizontal Cretaceous sedimentary rocks
of the Neuquén Group. The climatic conditions are extremely arid and the soils over bedrock are shallow,
consequently, the landscape is very breakable. These conditions are increased by the economic activities in
the region, mainly including hydrocarbon and farm works, which produce degrading effects against the
environment. Particularly, the seismic lines of hydrocarbons exploration, with removal of the superficial cover,
are important features where the hidric erosion might carried out (figure 3a and 3b). The length of the measured
lines from the satellital image in the Reserve, reach 1100 kilometre, which means a density of 10.4 meter per
hectares. The aim of this paper is to delimit different zones according to the expected intensity of the erosion
processes. These zones contribute to locate areas of special hazard where erosion could be increased
substantially, by extending sheet erosion, headward erosion of gullies or gully branching. The elaboration of
the erosion hazard map was based on different aspects. First, on combinations of permanent erosion factors,
inclination of slope, soil profile properties and lithology. And second, according the physiography of the region,
considering the variable factors natural vegetation cover, activities of the population and free soil percentage
following Bergsma (1983). All data were processed with Geographic Information System (GIS) using the
software Idrisi32. In the studied area, only the small scale topographic data (1:250000) were available, and the
slope of the small landforms can not be recognized. Therefore, the drainage network observed in the aerial
photographs and satellital imagery were used to estimate slope steep degree. The drainage network was
drew using fifty one stereoscopic aerial photograph, scale 1:60000 and, the density of drainage parameter
was measured within a grid of 1.2 square kilometre per 1.2 square kilometre. Considering the lithology,
landscape of the area, the stereoscopic observations and the measured at ground controls points, a correlation
between drainage density and slope steep degree was found. The drainage density turned out an important
complement of topographic map and constituted a good reference in order to delimit the areas with different
steep degree. Three qualitative classes of erosion hazard were recognized in the Auca Mahuida area: optimum,
acceptable and minimun, considering the methodology of land-use planning of Crozier et al (1974) and
Robinette y Crozier (1976). The classification indicates the degree of protection needed, as the erosion hazard
decrease from maximum to minimum. The combination of the different erosion hazard factors, mainly relief,
soil properties, free soil percentage (very important in the region) and natural vegetation allowed to delimit
sectors which include the following units of erosion hazard: 21.372 hectares (20.2%) comprises the optimum
class, 18.832 hectares (17.8%) the acceptable class and (62.0%) the minimum class. The different units
herein delimited were outlined in a map, providing the basis for a land-use planning and to prevent the erosion
in susceptible areas, which are priorities for the conservation (figure 4).