Abstract
Estimation of aquifer recharge is key to effective groundwater management and protection. In mountain hard-rock aquifers, the average annual discharge of a spring generally reflects the vertical aquifer recharge over the spring catchment. However, the determination of average annual spring discharge requires expensive and challenging field monitoring. A power-law correlation was previously reported in the literature that would allow quantification of the average annual spring discharge starting from only a few discharge measurements in the low-flow season, in a dry summer climate. The correlation is based upon the Maillet model and was previously derived by a 10-year monitoring program of discharge from springs and streams in hard-rock aquifers composed of siliciclastic and calcareous turbidites that did not have well defined hydrogeologic boundaries. In this research, the same correlation was applied to two ophiolitic (peridotitic) hard-rock aquifers in the Northern Apennines (Northern Italy) with well-defined hydrogeologic boundaries and base-outflow springs. The correlation provided a reliable estimate of the average annual spring discharge thus confirming its effectiveness regardless of bedrock lithology. In the two aquifers studied, the measurable annual outputs (i.e. sum of average annual spring discharges) could be assumed equal to the annual inputs (i.e. vertical recharge) based on the clear-cut aquifer boundaries and a quick groundwater circulation inferable from spring water parameters. Thus, in such setting, the aforementioned correlation also provided an estimate of the annual aquifer recharge allowing the assessment of coefficients of infiltration (i.e. ratio between aquifer recharge and total precipitation) ranging between 10 and 20%.
Highlights
Hard rocks cover approximately the 20–35% of the Earth surface and many are utilized as important aquifers (Amiotte Suchet et al 2003; Gustafson and Krásný 1994)
It is worth noting that the term ‘hard rock aquifer’ is generally related to igneous and metamorphic rocks (Dewandel et al 2006, 2011; Lachassagne 2008; Lachassagne et al 2011; Neuman 2005); in some circumstances, sedimentary rocks exhibit heterogeneous and anisotropic hydraulic conductivity distributions similar to those commonly observed for hard rock units, as in the case of the calcareous and siliciclastic turbidite formations in the Northern Apennines (Gargini et al 2014; Piccinini et al 2013)
Recession analysis with the Maillet model was performed on each spring hydrograph (Fig. 5) to determine α and the corresponding A and B parameters that drive the correlation between QA and QS
Summary
Hard rocks cover approximately the 20–35% of the Earth surface and many are utilized as important aquifers (Amiotte Suchet et al 2003; Gustafson and Krásný 1994). It is worth noting that the term ‘hard rock aquifer’ is generally related to igneous and metamorphic rocks (Dewandel et al 2006, 2011; Lachassagne 2008; Lachassagne et al 2011; Neuman 2005); in some circumstances, sedimentary rocks exhibit heterogeneous and anisotropic hydraulic conductivity distributions similar to those commonly observed for hard rock units, as in the case of the calcareous and siliciclastic turbidite formations in the Northern Apennines (Gargini et al 2014; Piccinini et al 2013) Such units behave as very transmissive aquifers in favorable structural conditions, as evidenced by Gargini et al (2006), Vincenzi et al (2009), and Vincenzi et al (2014) while investigating the hydrogeological effects induced by the drilling of a high-speed railway tunnel connecting Bologna and Florence (Italy). Since the investigated turbiditic aquifers do not have well-defined hydrogeologic boundaries and catchments, the proposed relationship could not be exploited for the estimation of aquifer recharge
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