Poster: Yrenda – Toba – Tarijeño Transboundary Aquifer System, South America: groundwater – surface water interaction

TUJCHNEIDER Ofelia "Faculty of Engineering and Water Sciences, National University of El Litoral, PO Box 217, Santa Fe, Argentina 2National Council of Scientific and Technical Research (CONICET)" Marcela PEREZ, Marta PARIS, Mónica D´ELIA (Faculty of Engineering and Water Sciences, National University of El Litoral, PO Box 217, Santa Fe, Argentina) conceptual model, mathematical model, transboundary aquifer, South America This paper presents the results of the activities carried out for the hydrogeological assessment and subsequent mathematical modeling of the groundwater flow in the transboundary aquifer system located beneath the alluvial fan of the Pilcomayo River between Ibibobo and Misión La Paz – Pozo Hondo (Argentina, Bolivia and Paraguay, South America). The aquifer system has an area of about 300,000 km2, fact that should be corroborated, since its limits should still be verified. For elaborating the preliminary conceptual groundwater model, the geologic formationsof the Tertiary and Quaternart period were taken into account as the stratigraphic sequence of hydrogeological interest. Jointly with the groundwater table map, available from previous works, the piezometric surface was quantified. Hydraulic gradient, hydraulic parameters, and groundwater velocities and flows were estimated. Using the analyses of both the geologic and hydrodynamic information, the preliminary conceptual groundwater model was defined, and it was possible to corroborate that the aquifer system behaves hydraulically as a multiunit. The construction of the mathematical model required a careful selection of the data because of the scarce basic information available according to the extension of study area and the purposes of the work. The calibration is well-considered because of the normalized root square error obtained (approximately 5%). The groundwater flow was clearly defined and it was also possible to quantify the bidirectional relation between surface water and groundwater. This fact had not been considered so far in earlier studies. Continue working on these bases will be essential to generate the plans for regional development and appropriate legal tools for the utilization and sustainable management. As a result of that, it will be possible to protect biodiversity, prevent desertification, and identify and prevent the effects of the climate change. All of this will be a genuine benefit to the inhabitants of this vast region.

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