THE USE OF THE HYDROLOGICAL MODEL SIMGRO AS A SUPPORT TOOL FOR GROUNDWATER MANAGEMENT IN AN IRRIGATED AREA IN MENDOZA, ARGENTINA

About 3% of the province consists of irrigated areas. The major crops are: vineyard 53%, fruit farming 17%, vegetables 11 %, fodder 8%, forest 6%, olives 3%, and others 2% (Estadisticas Agropecuarias de Mendoza 1988). The province has about 9 O00 km of irrigation canals. Of these, 500 km of primary and secondary canals are concrete-lined; the others are earth-lined. In the lower parts of the irrigation systems, there is also an extensive network of drainage collectors, with a length of approximately 2 500 km. In principle, only surface water is used for irrigation. Water is allocated on the basis of the area with irrigation water rights, but there are no precise figures of the actually cultivated area. In wet years, this practice has led to over-irrigation and, in certain areas, to a gradual rise in watertables. The result is often soil salinisation, which brings about a decline in productivity and a deterioration in the environment. On the other hand, during periods of drought, the inadequate distribution of scarce water reduces the production potential. The surface irrigation applications are then complemented with water pumped from subsurface aquifers. It has been estimated that, in the province of Mendoza, the area irrigated only with groundwater is 80 O00 ha, whereas that irrigated with both surface and groundwater resources covers approximately 30 O00 ha. In areas with surface water irrigation, there is in principle no need to use supplementary groundwater. Because of the misallocation of surface water, however, the need for groundwater exists, especially when vegetables are grown (Baars and van Logchem 1993). The conjunctive management of surface water and groundwater is a complex situation, in which hydrological models can be useful tools. One such model is the regional hydrological model SIMGRO, which can simulate the water flow in the saturated and unsaturated zones, and the flow of the surface water. It can take into account the effects of irrigation, drainage, groundwater use, and their impact on the evapotranspiration of different crops (Querner et a/. 1997). SIMGRO can analyze and evaluate specific operational measures and can quantify