Assessment of Saltwater Intrusion Risk at Mexilhoeira Grande - Portimão Aquifer (Portugal) by Indicator Geostatistics

The Algarve region, in Portugal, is strongly affected by the intense exploitation of its groundwater resources. The fact it is a coastal area implies that the management of these resources is of enormous complexity. Thus, there is a need to create capable tools for the evaluation of the risks and uncertainty associated to this case, so that risk maps can be made, and be used in the decision-making process related to the water resources manegement. A description of the uncertainty of this contamination problem can be achieved by using a non-parametric approach called Indicator Geostatistics. This involves the calculation of the probability distribution function of the unknown value at any location, conditioned to the available information. For this purpose a special coding must be used, to estimate the uncertainty of the chloride content. This is, can be treated by assigning binary indicator values according to some specific threshold. By using these categorical variables this formalism provide an estimation of the probability that the saline contamination in groundwater exceed a maximum admissible value. INTRODUCTION Groundwater has been widely used as one of the most important water resources. In the last three decades the southern part of the Algarve Province (located in the south of Portugal) has been over-exploited, due to the growth of tourism industry and to the changes of agriculture practices, specially in the summer period. Recently, serious problems are being caused by the improper and the excessive uses of groundwater. The sea water intrusion into aquifers is a typical and common problem in coastal areas. Over-exploitation of coastal aquifers create optimum conditions for the advance of the freshwater/saltwater interface which leads to some coastal aquifers contamination, which the Mexilhoeira Grande Portimão aquifer is one of them (Fig.1).