DRASTIC and GOD vulnerability maps of the Cabril River Basin, Portugal

Abstract

The main purpose of this study is to compare two methodologies, DRASTIC and GOD, applied to the basin of the Cabril River in determining groundwater vulnerability to pollution. The justification for the research work in this area relates to the fact that we are facing a basin adjoining the town of Vila Real (Portugal), with a propensity to expand into this area, and where there are many springs, both near the base of the basin and in hillside areas. As a result of the application, the GOD and DRASTIC maps were obtained. To better com-pare these final vulnerability maps, the conversion of the ranges of DRASTIC indices to a normal-ized scale from 0.0 to 1.0 value was performed, staying in the same rating scale as the GOD meth-od. It was observed, through the GOD method, that the area of the basin has mostly low or negligi-ble vulnerability, related to the high depth of the groundwater level and also to the low degree of confinement. Moreover, the results of the DRASTIC method indicate that most of the basin pre-sents medium to low vulnerability, especially in areas of higher altitude. However, both methods make high vulnerability correspond to areas covered by alluvium. It may be concluded from this study that the production of results using different methods of analysis, although with similar objectives, may differ in certain locations. Thus, the outlook for the future is that the vulnerability mapping techniques ought to include physical methods, improving the credibility of these studies.