Hydrogeological conceptual model of an irrigated agricultural area, Buenos Aires Province, Argentina

Abstract

In Argentina, the complementary irrigation has increased in most agricultural regions, where it is necessary to minimize possible negative impacts on the quantity and quality of groundwater. Numerical modeling techniques are used to obtain projections of the aquifer dynamics, for which a conceptual model is needed that provides the input data in the numerical simulations.A hydrogeological conceptual model for a rural area of Buenos Aires Province (Argentina), where complementary irrigation has caused significant depletion of groundwater levels during the irrigation season, has been developed. It was based on available geophysical and hydrogeological information and measurements of piezometric levels and hydraulic parameters of the aquifer together with the geochemical analysis of groundwater. This model was imported to a numerical model and the hydrogeological parameters were adjusted by the calibration with static piezometric levels measured in the wells. The conceptual model was validated satisfactorily using a fitting criterion to reach a value of root mean square error less than 5%. Different simulations of the probable drawdowns of the levels due to pumping were performed in the study area.The main hydrogeological unit is semi-confined, mostly comprising of a multilayer unit with good quality of water. Its minimum and maximum thickness was 60 and 240 m, respectively. The groundwater flows northwards from the hilly area to the plains. The recharge was 4.6 mm.year−1, representing 5% of annual precipitation. Dynamic simulations show that the aquifer gets dried, which questions its sustainability. The alternating condition of the source or drain of the streams depends on the irrigation period or the dry season, respectively. Great drawdowns of piezometric levels in some areas might be the cause of changes in water classification. These results lead to the need of planning the use of groundwater as a complement to agricultural activity, considering sustainable employment of the resource.