Screening of sustainable groundwater sources for integration into a regional drought-prone water supply system

摘要

This paper reports on the qualitative and quantitative screening ofgroundwater sources for integration into the public water supply system ofthe Algarve, Portugal. The results are employed in a decision support systemcurrently under development for an integrated water resources managementscheme in the region. Such a scheme is crucial for several reasons,including the extreme seasonal and annual variations in rainfall, the effectof climate change on more frequent and long-lasting droughts, thecontinuously increasing water demand and the high risk of a single-sourcewater supply policy. The latter was revealed during the severe drought of2004 and 2005, when surface reservoirs were depleted and the regional waterdemand could not be met, despite the drilling of emergency wells.For screening and selection, quantitative criteria are based on aquiferproperties and well yields, whereas qualitative criteria are defined bywater quality indices. These reflect the well's degree of violation ofdrinking water standards for different sets of variables, including toxicityparameters, nitrate and chloride, iron and manganese and microbiologicalparameters. Results indicate the current availability of at least 1100 l s−1 of high quality groundwater (55% of the regional demand),requiring only disinfection (900 l s−1) or basic treatment, prior tohuman consumption. These groundwater withdrawals are sustainable whencompared to mean annual recharge, considering that at least 40% ispreserved for ecological demands. A more accurate and comprehensive analysisof sustainability is performed with the help of steady-state and transientgroundwater flow simulations, which account for aquifer geometry, boundaryconditions, recharge and discharge rates, pumping activity and seasonality.They permit an advanced analysis of present and future scenarios and showthat increasing water demands and decreasing rainfall will make the watersupply system extremely vulnerable, with a high risk of groundwatersalinization and ecosystem degradation.