Improving our understanding and predictions of the impacts of groundwater extraction on small streams

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In the upper reaches of streams, where discharge is naturally low and flow may be seasonal, groundwater extraction for water supply may cause significant changes in base flow, stream stage, wetted area, velocity and temperature. Such alterations may reduce the availability of surface water downstream and have negative consequences for sensitive aquatic organisms. With heightened awareness and pressure in many Canadian jurisdictions to better manage the surface water impacts of groundwater extraction, and the increasing evidence of the negative effects of climate change, there is a significant need for research into the connection between groundwater extraction and flow conditions in small streams. The goal of the proposed NSERC Discovery research is to advance our understanding and methods for assessing and predicting the impact of groundwater extraction (by pumping wells) on the flow conditions and water temperature in small streams. To achieve this goal three short-term integrated projects are planned that include detailed field studies and subsequent data analysis and interpretation. The field program will focus on small streams in Prince Edward Island (PEI), Canada, where there is high public and regulatory awareness and concern surrounding the effects of groundwater extraction from the sandstone bedrock aquifer on small streams. The research will produce a unique high-resolution data set including changes in primary stream hydraulic parameters such as hydraulic gradients, width, wetted area, velocity, and temperature. The data from these field studies will be interpreted numerically using three-dimensional variably-saturated flow and heat transport models, and analytical models that remain popular in practice. Although various mathematical models, of varying complexity, exist for simulating stream flow depletion, accurate field experimental data that can be used to compare to various conceptual and mathematical models are surprisingly absent, especially so for small headwater streams. The proposed discovery research is expected be scientifically significant and highly suited to peer-reviewed publication, and have almost immediate impact on regulatory decisions for groundwater extraction permits in jurisdictions that are currently grappling with this water management issue.