Parameterization and quantification of recharge in crystalline fractured bedrocks in Galicia-Costa (NW Spain)

Abstract

Abstract. Quantifying groundwater recharge in crystalline rocks presents great difficulties due to the high heterogeneity of the underground medium (mainly, due to heterogeneity in fracture network, which determines hydraulic parameters of the bedrock like hydraulic conductivity or effective porosity). Traditionally these rocks have been considered to have very low permeability, and their groundwater resources have usually been neglected; however, they can be of local importance when the bedrock presents a net of well-developed fractures. The current European Water Framework Directive requires an efficient management of all groundwater resources; this begins with a proper knowledge of the aquifer and accurate recharge estimation. In this study, an assessment of groundwater resources in the Spanish hydrologic district of Galicia-Costa, dominated by granitic and metasedimentary rocks, was carried out. A water-balance modeling approach was used for estimating recharge rates in nine pilot catchments representatives of both geologic materials. These results were cross-validated with an independent technique, i.e. the chloride mass balance (CMB). A relation among groundwater recharge and annual precipitation according to two different logistic curves was found for both granites and metasedimentary rocks, thus allowing the parameterization of recharge by means of only a few hydrogeological parameters. Total groundwater resources in Galicia-Costa were estimated to be 4427 hm 3 yr −1 . An analysis of spatial and temporal variability of recharge was also carried out.

Sustainability of Groundwater Resources of Weathered and Fractured Schists in the Rural Areas of Galicia (Spain)

“…Inter ow is the major component of Q (78%), groundwater recharge is 19% of Q and surface runoff is approximately equal to 3% of Q (Table 1). The mean annual inter ow is equal to 771 mm while the annual aquifer recharge is equal to 185 mm which is consistent with the recharge estimated by Raposo et al (2012) with the chloride mass balance method in the Complex of Ordes.…”

“…The study area is mostly framed in metapsamites and metapelites of the Betanzos-Arzúa Unit (Fig. 2), which is part of the Complex of Ordes, a polymetamorphic unit with intercalations of amphibolites and ultrabasic intrusions (Anthonioz and Ferragne 1978;Galán et al 1978;Raposo et al 2012). Narrow insertions of phyllites can be found in the south of the study area which are less than 4 km long.…”

Hydrological response of a humid agroforestry catchment at different time scales

“…These rocks have low density of faults and fractures, which reduces the water storage capacity in the secondary porosity of the bedrock. Hence, groundwater recharge in the Órdenes Complex is assumed to be low: 8% of total rainfall (Raposo et al ., ) while soil water storage represents about 30% of the total rainfall according to Martínez‐Cortizas et al . ().…”

Fresh and saline submarine groundwater discharge in a large coastal inlet affected by seasonal upwelling

“…If we consider the average 222 Rn activities in the regolith aquifer unit as representative of the continental groundwater endmember for each box, the volumetric discharge of fresh groundwater into the Ría de Vigo would be The surface aquifer unit contained in crystalline rocks and within the regolith has three orders of magnitude higher volumetric water storage capacity than the fractured bedrock underneath. The surface unit also has higher recharge/discharge rates and lateral transmissivities by several orders of magnitude (Mota et al 2004;Ramalho et al 2012;Raposo et al 2012). Thus, the groundwater contained within the regolith is most likely to be the dominant continental groundwater endmember in fresh submarine groundwater discharge into the Ría de Vigo.…”