The occurrence and movement of groundwater in hardrock terrains are mainly controlled by secondary permeability triggered by fracturing. Mapping and monitoring of groundwater resources and estimation of future resources are key issues in hardrock regions. Conventional methods used to the identification, delimitation and mapping of groundwater potential zones are mainly based on ground surveys using geological, morphotectonics, geophysical and hydrogeological tools. Delineating groundwater potential zones using remote sensing and Geographical Information Systems (GIS) is a rapid and cost-effective tool to generate valuable geo-data. Hydrogeomorphology deals with the interaction of geomorphic processes relating surface water and groundwater, connecting, namely, physical geography, geomorphology, geology, hydrogeology, remote sensing and climatology. Hydrogeomorphology can be applied to the definition of areas of higher infiltration and of higher potential for groundwater circulation. The Infiltration Potential Index (IPI) is reliant on several factors (e.g., lithology, structure, weathering grade, tectonic lineaments, land use, drainage, slope, rainfall) which can be overlapped and cross-linked in a GIS environment. In urban areas, this index should be complemented with anthropogenic and urban hydraulic features, like the water supply, the sewer and the stormwater networks. In the urban framework it is called Infiltration Potential Index in urban areas (IPI-urban).
The aim of this work was to delineate the groundwater potential zones in the urban area of Viana do Castelo (NW Portugal). A combination of GIS and Analytical Hierarchical Process (AHP) techniques was used. This methodology took advantage of remote sensing and hydrogeomorphological mapping, accompanied by a hydrogeological inventory fieldwork. Hydrogeomorphological mapping and 8 thematic layers (land use, geology, tectonic lineaments density, slope, drainage, water supply system, stormwater network and sewage network densities) were prepared for groundwater potential zones delineation. Weights assigned to each class in all the thematic maps are based on their characteristics and water potential capacity through multi-criteria AHP method. Land use plays an important role: urban and industrial areas cover the largest part (60%). Geology also has a key role: alluvia, fluvial and marine deposits are the most representative (49%) and two-mica granite, medium to coarse grained, is the second more representative lithology (36%). Tectonic lineaments show a density < 4 km/km2 for most of the area (72%). Slopes are mostly gentle to very gentle (< 3°, 57%). Drainage density is frequently < 1.5 km/km2 (76%). Stormwater network densities are frequently < 8 km/km2 (52%). For the sewage network, most of the area has a density < 10 km/km2 (53%). The water supply system densities are mostly < 21 km/km2 (70%). Consequently, it was possible to achieve a prevalent (70%) Moderate to Low (40–60) IPI-Urban in this study area.
This study provides insights for decision makers for appropriate planning and management of groundwater resources in urban regions.