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Report: Modelling Tools for Estimating Effects of Groundwater Pumping on Surface Saters

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This report presents a literature review of surface water - groundwater (SW-GW) interactions, including cases studies in BC, and an approach for characterizing SW-GW connectivity based on the BC aquifer classification scheme. It provides an evaluation of modelling approaches for quantifying effects of groundwater withdrawals on surface waters, particularly analytical models that are simple to implement. Modelling approaches for assessing impacts from groundwater withdrawals are recommended.

Author:  Rathfelder, Klaus

Date Published:  Nov 2016

Report ID:  51878

Audience:  Government and Public

Surface water and groundwater are closely linked in the hydrologic cycle. Groundwater discharges to surface waters, including streams, lakes, springs, and wetlands, often constitute a high fraction of flows and water levels in surface waters. In particular, groundwater discharges to streams frequently comprise a high percentage of baseflow, up to 100% of baseflow during seasonal dry periods, and these discharges can be essential for maintaining healthy aquatic habitats, including high value fisheries. Pumping groundwater from aquifers that discharge to surface waters can reduce flows and water levels of the hydraulically connected surface waters. This can deplete the amount of surface water available for allocation, can affect the existing surface water rights, and can harm aquatic health when flows fall below minimum thresholds for environmental flow needs (EFNs). Increasing the distance between the well and the stream or surface water does not necessarily diminish the effects of surface water depletion, rather it delays the impacts over time, sometimes for years. Sustainable allocation of groundwater resources and protection of aquatic habitats requires an understanding of the hydraulic connectivity between water wells and surface water resources. The existing aquifer typing system provides a basis for broadly categorizing SW-GW interaction in province. Modelling tools provide a means for assessing and evaluating in SW-GW interactions and can provide estimates of streamflow responses to groundwater pumping. Analytical models use idealized conceptualizations of the natural system to obtain simplified solutions that are generally easy to solve with limited data requirements. They are useful for gaining insights into system behavior and as screening tools for management of groundwater diversion and use. Alternatively, numerical groundwater models attempt to capture hydrogeologic complexities that vary in space and time, providing tools for more comprehensive basin scale management. However, numerical models are time consuming, costly and difficult to construct and calibrate, and are not available to support groundwater allocation throughout the vast majority of the province. Eight analytical models were tested and evaluated through inter-model comparison with a calibrated numerical model of the Grand Forks aquifer. Each of the analytical models provided conservative estimates of streamflow depletion in the sense that they overestimate the rate of streamflow depletion and recovery in comparison to numerical solutions. This report presents guidance for selecting and using analytical models, based in part on these model comparisons. Recommendations to support allocation staff in groundwater licensing are: Promote ongoing awareness and dialogue of SW-GW connectivity and potential impacts. Support studies and monitoring activities to improve understanding of SW-GW connectivity in the province. Use a conservative approach in high priority, high impact areas. Support groundwater modelling training for government staff in order to promote use and appropriate review of groundwater models used in groundwater license applications. Use available spreadsheet tools developed by Bruce Hunt for analytical modelling of SW-GW interactions. Support development of comprehensive groundwater management models for assessing groundwater allocation and groundwater management strategies in high priority areas of the province.

Report Type
  Region - Province Wide
  Water Information - Groundwater

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