Quantifying Streambed Dispersion in an Alluvial Fan Facing the Northern Italian Apennines: Implications for Groundwater Management of Vulnerable Aquifers

Groundwater management of alluvial aquifers facing the northern Italian Apennines is an important issue that is becoming more complicated due to ongoing climate changes and increased water demands. The large groundwater withdrawals, coupled with an overall worsening of the water quality, require detailed knowledge of the recharge mechanisms of these aquifers that can be useful for further adaptation measures. We have focused our attention on a selected alluvial fan in which 49 slug injections of hyperconcentrated solutions of NaCl allowed river discharges to be estimated in seven different hydraulic sections. Consequently, losses from the streambed were assessed for the six river reaches along with the corresponding uncertainties in the estimates. The study confirms the suitability of such tests for identifying sectors in which streambed losses are promoted and for quantifying the total recharge conveyed to underlying aquifers. In addition, it has been demonstrated that the total streambed losses can be further linked to river discharges in any gauge upstream of the alluvial fan thanks to linear regression. Once obtained, the latter makes monitoring groundwater recharge by stream losses in real time possible if a permanent measurement device (such as the common telemetry used for river discharge monitoring) is available.