The Groundwater Flow of the Guaraní Aquifer System Outcrop Region in Uruguay: New Research Generates New Questions

Abstract

The Guarani Aquifer System (GAS) (Argentina, Brazil, Paraguay and Uruguay) represents a typical transboundary aquifer. In Uruguay, the rocks that make up the GAS extend for about 36,000 km2 of which about 4,900 km2 correspond to outcrop areas, while the rest is covered by basalts. This contribution addresses aspects of the dynamics of the GAS in Uruguayan territory, focused on the outcropping region and its adjacent areas. This behavior is conditioned by the control of the relief associated with the main morphostructural elements that, in turn, condition the drainage network of the main surface water courses. Regarding the analysis of the geomorphology and main structural guidelines of this area, three hydrodynamic domains can be distinguished. In the Northern Domain, groundwater flows to the S, controlled to the West by the Negra and Haedo ridges and to the North, by the Santa Ana ridge. In the Central Domain, the direction of groundwater flow is to the SE, controlled to the west by the Cuchilla de Haedo and a NW-SE drainage network that finds the Tacuarembó River as its base level. In the Southern Domain, the flow is towards the E with a slight south-southeast variation. The piezometric maps show this regional flow trend towards the east, as well as the discharge of the aquifer in the main water courses that cross the study area. Additionally, a base flow analysis was carried out in the hydrographic basin of the Tacuarembó River, showing a significant discharge of the aquifer in the rivers and streams with BFItotal values ​​of 29 .7% to 36.3%. This new model challenges existing opinions on the main regional GAS recharge areas, highlights the need to review water management strategies, as well as the need for further research on GAS dynamics in confined areas, including in this analysis transboundary flows.

Keywords: groundwater flow, Guaraní Aquifer System, Piezometry, discharge, Baseflow analysis