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Groundwater pumping can lead to streamflow depletion and thus affect environmental flow needs. This project evaluated analytical depletion functions and found they are accurate tools to predict streamflow depletion and the response time to environmental flow thresholds. However, the performance of analytical depletion functions varied in different hydrogeologic settings. Both numerical model and analytical depletion functions can lead to biased results if not properly constructed, or misapplied.
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Author: Qiang Li, Samuel C. Zipper, Tom Gleeson
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Date Published: Jun 2020
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Report ID: 58704
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Audience: Government and Public
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Groundwater pumping can negatively affect surface water by reducing groundwater discharge into them or inducing infiltration through the streambed. Combined, these impacts are known as streamflow depletion. Understanding streamflow depletion can guide water management for issuing sustainable groundwater licenses while maintaining environmental flow needs.
Recently, analytical depletion functions have been suggested as rapid and accurate tools for streamflow depletion assessment, but their performance has only been tested in a few hydrogeological settings. To evaluate whether they will be useful tools for other regions with contrasting stream network and hydrogeological characteristics. Another notable negative impact of groundwater pumping on streamflow is the time taken for streamflow depletion to reach the environmental flow threshold, i.e. response time to environmental flow threshold. In this report, we compared analytical depletion functions to calibrated MODFLOW models in BX Creek and Peace Region with distinct hydrogeological settings and spatial scales in B.C.
In the BX Creek domain, analytical depletion functions correctly identified the most affected stream segments for all wells over the entire 30-year simulation with the average normalized MAE of 14.4% (mean absolute error). For all affected stream segments, the average normalized MAE was 5.0%. In the Peace region, the analytical depletion functions correctly identified the most affected stream segment for fewer wells than the BX Creek domain, but can reach up to 83% of the time. The average normalized MAE was 7.6% for the most affected segment and 2.3% for all stream segments. Overall, these comparisons indicated that analytical depletion functions can be an accurate tool for estimating streamflow depletion within the pumping season at over annual to decadal timescales, with worse performance for sub-annual depletion.
The performance of analytical depletion functions varied in response to the hydrogeologic settings. Analytical depletion functions had smaller errors for wells in higher hydraulic conductivity materials, screened in shallower aquifers, and affecting segments with lower streambed conductance in the BX Creek. Conversely, in the Peace region, analytical depletion functions had smaller errors in lower hydraulic conductivity materials and deeper aquifers, while the performance over the range of streambed conductance conditions tested was similar. In both domains, there was consistently greater difference between analytical depletion functions and MODFLOW for wells within a few kilometers of a stream, which correspond to wells with the highest predicted depletion. The contrasting responses of analytical depletion functions performance to the hydrogeological setting between the BX Creek and Peace region models indicates that different drivers influence the accuracy of streamflow depletion prediction in different hydrogeological settings.
Moreover, realistic groundwater pumping in the two domains leads to depletion exceeding a presumptive standard for protecting environmental flow needs, indicating that potential groundwater pumping in study domains should be considered in water management. In the BX Creek, the difference in response time to environmental flow threshold between analytical depletion functions and MODFLOW in the BX Creek was smaller (~ 2 years) than the difference between models in the Peace region, while analytical depletion function showed both shorter and longer response time than MODFLOW. While, in the Peace region, the analytical depletion functions showed shorter response times than MODFLOW. These results indicate that analytical depletion functions can be used to estimate the response time of environmental flows, but potential errors resulting from the local hydrogeological setting should be considered.
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Report Type
Subject
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Region - Province Wide |
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Water Information - Groundwater |
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Water Information - Water Management |
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