Water in Celtic Countries: Quantity, Quality and Climate Variability (Proceedings of the Fourth InterCeltic Colloquium on Hydr

Water in Celtic Countries: Quantity, Quality and Climate Variability (Proceedings of the Fourth InterCeltic Colloquium on Hydrology and Management of Water Resources, Guimarães, Portugal, July 2005). IAHS Publ. 310, 2007, 161-171.

Assessing aquifer vulnerability to seawater intrusion using the GALDIT method: part 1—application to the Portuguese Monte Gordo aquifer

JOÃO PAULO LOBO FERREIRA¹, A. G. CHACHADI², CATARINA DIAMANTINO¹ & M. J. HENRIQUES¹

1Laboratório Nacional de Engenharia Civil (LNEC), Hydraulics and Environment Department (DHA), Groundwater Division (NAS), Av. do Brasil, 101, 1700-066 Lisboa, Portugal

lferreira@lnec.pt

2 Goa University, Dept. of Earth Science, Goa University, Goa–403 206, India

Abstract This paper is divided into two parts. Part 1 presents the first application in Europe of an index developed in the framework of the EU-India INCO-DEV COASTIN project that aims to assess coastal aquifer vulnerability to seawater intrusion. The most important factors controlling seawater intrusion were found to be: Groundwater occurrence (aquifer type; unconfined, confined and leaky confined); Aquifer hydraulic conductivity; height of groundwater Level above the sea level; Distance from the shore (distance inland perpendicular from shoreline); Impact of existing status of seawater intrusion in the area; and the Thickness of the aquifer that is being mapped. The acronym GALDIT is formed from the highlighted letters of the parameters for ease of reference. These factors, in combination, were found to include the basic requirements needed to assess the general seawater intrusion potential of each hydrogeological setting. GALDIT factors represent measurable parameters for which data are generally available from a variety of sources without detailed examination. A numerical ranking system to assess seawater intrusion potential in hydrogeological settings has been devised using GALDIT factors. The application of the method is exemplified in the paper for the assessment of aquifer vulnerability to seawater intrusion in Portugal (Monte Gordo aquifer in the Portuguese southern Algarve region). The system contains three significant parts: weights, ranges, and ratings. Each GALDIT factor has been evaluated with respect to the others to determine their relative importance. In Part 2 of the paper the method for assessing GALDIT index parameters is fully explained.

Key words aquifer vulnerability; groundwater protection; modelling; sea water intrusion