The knowledge of the hydraulics and the intrinsic properties of the hydrogeologic units is fundamental for the sustainable use of the hydric resource in a basin. The objective of this study is to accomplish an integrated analysis of the hydrologic system of the Maullín river basin (a lacustrine basin covering approximately 4.300 km2), focused on determining the dynamics of groundwater and the properties of the materials where the water flows. It was developed on the basis of geology, geophysical prospecting and water well information (referring to its stratigraphy and pumping tests), which define the hydrogeologic units and the piezometry, from which groundwater flow is deduced. From the integration of the information it was established that the hydrogeologic units of high potential for water extraction are of granular type and are found, mainly, in sedimentary deposits of the Pleistocene-Holocene of glacial and glaciofluvial origin, harboring confined and unconfined aquifers. These units are connected to each other, so they can be considered as a large aquifer system. The very low hydraulic conductivity units are associated to the metamorphic rocks of the Paleozoic-Triassic and to intrusive rocks with granitic composition of Oligocene -Miocene, which constitute the impermeable basement. Based on the information from the water wells, an analysis was carried out on 233 pumping tests, obtaining estimates of their transmissivity. The results showed a maximum of 9.480 m2/day and a minimum of 0,8 m2/day. The statistic analysis of the transmissivity allowed to compare the water extraction capacity of the different units and to define the characteristic ranges of the most important ones. The storage coefficient could be estimated from a single pumping test that had record levels in an observation well, which resulted in a value of 0,002.
The basin piezometry is closely related to the surface morphology, where the topographic highs coincide with the areas with the highest elevation in the piezometric surface. This condition indicates that the main source of recharge of the aquifer system has its origin in rainfall and that the relationship between the Maullín river and its main tributaries, with the aquifer system is of the effluent river type. In addition to this, the piezometry shows a lateral outlet at the south of the basin
With the information given by the piezometry and the hydraulics properties of the hydrogeologic units we can conclude that the water received by the soil and the vegetation cover, is divided into a evapotranspiration, surface runoff and a third component that infiltrates to join the aquifer system. The main outlet of groundwater is the discharge to the bodies of surface water, to which are added: the water extractions by pumping wells and the lateral outlet of the basin.