Hard rock aquifers (or discontinuous aquifers) are commonly intended as igneous or metamorphic rocks with very low primary porosity and a significant however discontinuous and strongly anisotropic secondary porosity (i.e. fractures) due to tectonic stresses and weathering. In some cases, the term “hard rock aquifer” is well suited also for sedimentary fractured rocks. This is the case of the turbiditic formations in the Northern Apennines (Italy), that represent the most valuable groundwater reservoir in the region. In such cases, the quantification of water resources hosted in the hard rock aquifers becomes of paramount importance. We propose a method to quantify the effective recharge occurring within a spring recharge area in a hard rock aquifer setting when only spring discharge monitoring during the low flow season (summer) is available. An empirical relationship was found between the average annual discharge of a spring and its average summer discharge, starting from a large database of 11 hydrologic years of discharge monitoring on more than 80 springs. Such relationship is linear on a log-log scale and changes according to the Maillet’s recession coefficient. The average annual flow rate obtained from summer monitoring data (i.e. the average summer discharge and the Maillet coefficient) is considered as a proxy of the effective recharge occurring within the spring recharge area. The proposed method was tested both in turbiditic and ophiolitic hard rock aquifers in the Northern Apennines in different hydrologic years, providing an overall accuracy in the range of ±15% with respect to the actual annual average spring discharges. Thus, this is a promising tool to support the application of hydrologic balances in hard rock aquifers. However, further tests should be carried out in different hard rock aquifer settings in order to form a basis for more realistic expectations about the overall validity of the method.
Estimation of effective recharge in hard rock aquifers based on spring discharge monitoring during the low flow season / Maria Filippini, Stefano Segadelli, Anna Monti, Alessandro Gargini. - STAMPA. - (2018), pp. 691-691. (Intervento presentato al convegno Congresso SGI-SIMP "Geosciences for the environment, natural hazards and cultural heritage" tenutosi a Catania nel 12-14 settembre 2018).
Estimation of effective recharge in hard rock aquifers based on spring discharge monitoring during the low flow season
Maria Filippini
;Alessandro Gargini
2018
Abstract
Hard rock aquifers (or discontinuous aquifers) are commonly intended as igneous or metamorphic rocks with very low primary porosity and a significant however discontinuous and strongly anisotropic secondary porosity (i.e. fractures) due to tectonic stresses and weathering. In some cases, the term “hard rock aquifer” is well suited also for sedimentary fractured rocks. This is the case of the turbiditic formations in the Northern Apennines (Italy), that represent the most valuable groundwater reservoir in the region. In such cases, the quantification of water resources hosted in the hard rock aquifers becomes of paramount importance. We propose a method to quantify the effective recharge occurring within a spring recharge area in a hard rock aquifer setting when only spring discharge monitoring during the low flow season (summer) is available. An empirical relationship was found between the average annual discharge of a spring and its average summer discharge, starting from a large database of 11 hydrologic years of discharge monitoring on more than 80 springs. Such relationship is linear on a log-log scale and changes according to the Maillet’s recession coefficient. The average annual flow rate obtained from summer monitoring data (i.e. the average summer discharge and the Maillet coefficient) is considered as a proxy of the effective recharge occurring within the spring recharge area. The proposed method was tested both in turbiditic and ophiolitic hard rock aquifers in the Northern Apennines in different hydrologic years, providing an overall accuracy in the range of ±15% with respect to the actual annual average spring discharges. Thus, this is a promising tool to support the application of hydrologic balances in hard rock aquifers. However, further tests should be carried out in different hard rock aquifer settings in order to form a basis for more realistic expectations about the overall validity of the method.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
