Abstract
This study sums up the first estimates of the young water fraction (Fyw; here understood as the percentage proportion of groundwater passing through the well’s screen and younger than approximately 2–3 months) from groundwater collected in 75 wells from alluvial fans facing the northern Italian Apennines of Italy. The Fyw estimates were based on a monthly dataset of water-stable isotopes (oxygen-18 (18O)) from surficial water (9 rivers), while the dataset of groundwater (75 wells) consisted of three-monthly isotopic data. In the cases of surficial water and stable isotopes, these lasted over the period of January 2003 to December 2007, while in the case of groundwater, the data were collected from January 2005 to December 2007. The values of Fyw were estimated by means of a sine-wave fitting technique; the results made evident the presence of unexpectedly reduced differences between groundwater. In particular, shallower groundwater hosted in aquifers from the apical parts of the alluvial fans (i.e., aquifers characterized by the coarsest materials such as gravels and sands, and closest to the recharge areas) showed similar values of Fyw to the deepest aquifers from the distal parts; however, former studies mentioned here evidenced the existence of poorly recharged old groundwater. Our results seem to confirm a complex behavior of these aquifers compared with what had previously been thought.
Highlights
Published: 20 February 2022In Italy, the alluvial fans of rivers flowing out from the northern Apennines and Alps have always been considered the main recharge zones for aquifers hosted in the Po Plain [1].The Southern sector of the Po Plain faces the northern Apennines and groundwater recharge is focused there in the apical part of the alluvial fans [2,3,4], where both streambed dispersion and rainfall percolation from the topsoil are promoted by the wide outcrops of coarser materials, such as gravels and sands
By passing to the wells, their DAP varied from 3300 m (Enza River) to about 50,000 m (Reno River)
If a well is placed in the ideal case of a homogenous and isotopic aquifer, the groundwater pumped to the surface is composed of water molecules that have travelled several
Summary
In Italy, the alluvial fans of rivers flowing out from the northern Apennines and Alps have always been considered the main recharge zones for aquifers hosted in the Po Plain [1]. The Southern sector of the Po Plain faces the northern Apennines and groundwater recharge is focused there in the apical part of the alluvial fans [2,3,4], where both streambed dispersion and rainfall percolation from the topsoil are promoted by the wide outcrops of coarser materials, such as gravels and sands. After reaching the groundwater hosted in the apical part of the alluvial fans, water molecules start to move northwards, driven by a reduced hydraulic gradient (up to 0.001). The time required by water molecules to reach the distal part of the alluvial fans differs depending on flow paths. With simultaneous reduction in the hydraulic conductivities and departure from the main
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