IWRA Proceedings

Groundwater pumping can affect streamflow by reducing groundwater discharge to streams and/or inducing streamflow losses to groundwater, which are defined collectively as streamflow depletion. Understanding the linkages between groundwater pumping and streamflow depletion is challenging and important for preventing impacts to aquatic ecosystems and managing water sustainably. Numerical models require substantial investments to develop, calibrate and validate; however, such expert systems are not able to be interacted with directly by non-experts or public.

Limited access to actionable information however makes it hard/impossible for sustainable outcomes to be achieved. In response to this challenge we have developed a web-based decision support tool for public use, which is based on newly developed analytical depletion functions (published under open source licenses) that can apportion streamflow depletion from groundwater pumping to nearby streams in real-world settings with complex hydrogeological landscapes and stream networks. The goal of the tool is to provide robust, clear, and transparent access to results using flexible web technologies. We evaluated the performance of analytical depletion functions compared to numerical models in a range of hydrologic landscapes. Our results show that analytical depletion functions provide comparable information to numerical models with substantially less time and effort. Our online decision-support tool can also provide basic information on the timing and magnitude of streamflow depletion from existing, and new wells in an easily digestible format which will improve the effectiveness of sustainable management efforts.

We identified that input data quality is a critical factor in producing streamflow depletion estimates for both analytical and numerical approaches. We stress that although numerical models are the standard for streamflow depletion assessments, when they have been developed for other purposes, they cannot be directly applied for streamflow depletion assessment. Moreover, even calibrated numerical models for estimating streamflow depletion can have mass balance errors greater than depletion estimates and result in significant uncertainties when used for streamflow depletion assessment. These limitations should be considered in future studies. Presenting streamflow depletion from groundwater pumping in the context of surface water supply (past, present, and future), existing water demands, and environmental flow needs provides the foundation for enhanced management, planning, and prioritization of expanded monitoring efforts.