Groundwater recharge in urban areas (Porto, NW Portugal): the role of GIS hydrogeology mapping

A delineation of groundwater potential zones was performed and an urban infiltration potential index (IPI-Urban) was proposed. The pilot site was the Paranhos and Salgueiros water galleries and surroundings in Porto City (NW Portugal). An integrated approach combining hydrogeomorphology and GIS was developed applying multiple layers of information (tectonic lineaments, hydrogeotechnical units, slope, drainage, land use, sewage and stormwater networks, water supply system and rainfall). Different ranks were assigned to thematic layers and classes received different weights according to their contribution to define groundwater potential areas using the AHP methodology. Two scenarios, Summer and Winter, were computed. 81% of the region is covered by urban and industrial areas and streets. Three areas were identified for major potential direct groundwater recharge (SE of Arca d´Água site, E-SE of Burgães site and W-NW of Lapa site). A Moderate to Low IPI-Urban prevails, and the High and Very high IPI-Urban appear mainly along the three cited valleys. A low to very low recharge was estimated, with less than 50 mm/year and 6% on the Winter scenario. Aquifer potential yields in the Winter scenario are in the range of 1–2 L/s/km². The IPI-Urban is a valuable tool for integrated water resources management in urban areas.