Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain)

Naves, Acacia; Samper, Javier; Pisani, Bruno; Mon, Alba; Dafonte, Jorge; Montenegro, Luis; García-Tomillo, Aitor

Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain) | Hydrogéologie et gestion des eaux souterraines dans une zone granitique côtière avec des pentes fortes en Galice (Espagne) Hidrogeología y gestión del agua subterránea en una zona granítica costera de Galicia (España) con pendientes pronunciadas 西班牙Galicia陡坡沿海花岗岩地区的水文地质学和地下水管理 Hidrogeologia e gestão das águas subterrâneas em uma zona costeira granítica com encostas íngremes na Galícia (Espanha)

2021

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m³/day.

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