Flux tracking of groundwater via integrated modelling for abstraction management.

• An integrated water system model with a reduced-complexity groundwater module. • The model performs well in simulating river and groundwater temporal dynamics. • A novel flux tracking approach to reveal groundwater and river baseflow origins. • Assessment of aquifer bodies' contributions to baseflow and groundwater abstraction. • Strategies informed by flux tracking results improve baseflow more efficiently. In systems where surface water and groundwater interact, management of the water resource often involves conflicting objectives between water supply and baseflow maintenance. Balancing such objectives requires understanding of the role of groundwater in integrated water systems to inform the design of an efficient strategy to minimise abstraction impacts. This study first develops a reduced-complexity, processed-based groundwater model within the water systems integration modelling framework (WSIMOD). This model is applied to the Lea catchment, UK, as a case study and evaluated against monitored groundwater level and river flow data. A flux tracking approach is developed to reveal the origins of both river baseflow at a critical assessment point and abstracted groundwater across the systems. The insights obtained are used to design two strategies for groundwater abstraction reduction. Results show that the model has good performance in simulating the groundwater and river flow dynamics. Three aquifer bodies that contribute the most to the river baseflow in the dry season at the assessment point are identified; contributions being 17 %, 15 %, and 5 %. The spatial distribution of abstracted groundwater originating from these aquifer bodies is illustrated. Compared to the default equal-ratio reduction, the strategy prioritising abstraction reduction in these three aquifer bodies increases a similar amount of baseflow (13 %) by reducing much less abstraction (23 %). The other strategy, which further decreases abstraction in the adjacent aquifer bodies, increases more baseflow (16 %) with a similar abstraction reduction (30 %). Both strategies can more efficiently improve the baseflow. The flux tracking approach can be further implemented to trace water from other origins, including runoff, stormwater, and wastewater, to enable coordinated management for better systems-level performance. [ABSTRACT FROM AUTHOR]