Hydrogeological characterization and water use of a sector of sands, sandstones and gravel on the coast of Baixo Alentejo

This reasearch discusses the necessary tasks to carry out the hydrogeological characterization of the sands, sandstones, and gravels of the Baixo Alentejo coast. Currently, this characterization has done in detail only in the areas where these formations constitute hydro-stratigraphic units of the aquifer systems of Sines and the Alvalade Basin. In addition to system hydrogeological characterization of the system, the volume of water used for irrigation in the study area was estimated, with the aim of characterizing its inter-annual evolution between 2000 and 2018 and intra-annual for the year 2018. To do so, remote sensing and satellite image processing methods were used (LANDSAT 5 and 8 and MODIS). A synthesis of the hydrogeological characterization is presented in an area of 195.8 km², divided into two aquifer sectors, one located north of the Mira River with 94.12 km² and the other south with 101.75 km². The first stage of the work consisted of the analysis of the studied aquifers recharge based on precipitation and the analysis of piezometry data in order to define the conceptual model of hydraulic functioning of the system. The available data were obtained from fieldwork and from the LIFE-Charcos Project (LIFE12NAT / PT / 997). In parallel, an analysis of land use and occupation performed, with emphasis on the identification of irrigation areas. Finally, the volume of water used in agriculture irrigation was determined using the method of estimating the consumptive use of water in irrigation at a local scale, based on the determination of evapotranspiration values, using the algorithm SEBAL, precipitation, and  irrigation efficiency. The results obtained were validated, with high precision, through the comparison with the irrigation volumes known during 2018, and the calibration of the monthly sequential water balance model at ground level.

Key words: aquifer system of sands, sandstones and gravels of the Baixo Alentejo coast; hydrogeology; Irrigation; Remote Sensing.