Longer drought periods, increasing water demand, and growing conflicts between drinking water supply, water protection, and ecological requirements are placing increasing pressure on the management of groundwater and surface water resources. In valley aquifers with strong hydraulic connectivity between rivers and groundwater, abstractions, artificial recharge, and operational controls can substantially affect river discharge during low-flow conditions (Figure 1). At the same time, measures such as Managed Aquifer Recharge (MAR) and Managed Surface Water Recharge (MSWR) are gaining importance as tools to stabilize water availability, ecological functions, and supply security in the long term. However, the targeted implementation of such measures requires a detailed understanding of local river-groundwater interactions and the temporal response of the system to operational interventions.

At the Wühre pilot site (Sissach, Ergolz catchment; Figure 1), the impacts of groundwater abstraction on low-flow conditions in the Ergolz River are being investigated. During dry periods, pumping from the drinking water wells Wühre 1-3, located close to the river, can significantly aggravate low-flow conditions. Since 2025, a new control system implemented by the Sissach water utility has enabled optimized pumping strategies. Based on an already calibrated groundwater flow model, a targeted field experiment during a low-flow period is planned to quantitatively assess the effects of different pumping strategies on river discharge and groundwater levels, and to further optimize operation.

In the Frenke catchment (Niederdorf-Hölstein; Figure 1), the focus is on artificial groundwater recharge of the valley aquifer. A comprehensive monitoring and modeling framework investigates how infiltrated water from the ARA Frenke II site influences groundwater dynamics and the discharge of the Vordere Frenke. Model results indicate that even moderate recharge rates can make a relevant contribution to low-flow discharge. In addition, the Helgenweid site is being evaluated for measures to enhance groundwater exfiltration into the Frenke, for example by directly discharging groundwater into the river during dry-weather conditions. Planned field experiments will quantify the hydrological effects of this measure and assess its suitability as an adaptation strategy for low-flow conditions.