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Abstraction of groundwater from a well beside a stream can result in depletion of stream discharge. The ability to estimate stream depletion due to pumping is necessary for water rights management, which requires an understanding of hydraulic connectivity between aquifers and streams. Evaluation of hydraulic connectivity is required for water licensing decisions in BC under the WSA. This report documents the results of a field study on interaction between groundwater and sensitive streams.
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Author: Hall, Glen; Allen, M.; Simpson, M.; Tolera, H.; Jackson, B.; Middleton, M.A.; Lepitre, M.
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Date Published: Sep 2017
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Report ID: 52918
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Audience: Government and Public
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Abstraction of groundwater from a well beside a stream can result in depletion of stream discharge. The ability to accurately estimate stream depletion due to pumping is necessary for water rights management. In BC, evaluation of hydraulic connectivity is required for water licensing decisions. The purpose of this study was to build an understanding of the interaction between groundwater and sensitive streams. The study consisted of two parts: (1) a targeted Phase 1 field investigation in Langley, BC aimed at determining the impacts of pumping on aquifer-stream interactions, and (2) a multi-level regional stream vulnerability assessment in the Lower Fraser Valley for determining the vulnerability of other similar types of stream-aquifer systems in order to identify streams that might be similarly impacted by groundwater abstraction. This report documents the results of the Phase 1 field investigation. Middleton and Allen (2017) report on the multi-level regional stream vulnerability assessment.
Three wells were drilled at the study site near Union Creek (a tributary to the Salmon River, a stream with allocation restrictions); one was completed as a pumping well and two as monitoring wells. Core logging revealed three hydrostratigraphic units: a soil layer about 1 m thick, a gravelly-sand aquifer approximately 10 m thick, and a lower clay unit. The aquifer is unconfined, with flow directed to Union Creek, although the hydraulic gradient changes in magnitude and direction seasonally.
Slug and bail tests were analyzed to obtain a preliminary estimate of hydraulic conductivity of the aquifer. A low-rate pumping test was conducted in July 2016, providing preliminary estimates of transmissivity, specific storage and specific yield. A high-rate pumping test was conducted in December 2016. The degree of aquifer-stream connectivity was determined using head measurements in instream nested piezometer pairs, seepage meter measurements, and stream stage measurements coupled with streamflow measurements.
During the high-rate pumping test, drawdown was not evenly distributed along the streambed. All deep instream piezometers showed more drawdown than their shallow counterparts. Water levels recovered in all piezometers during recovery and seepage decreased slightly over the test. Stream stage dropped at all hydrometric stations following the short duration step test and recovery, and continued to drop prior to and throughout the high-rate pumping test. A heavy snowfall event during the step test appears to have influenced stream level. The change in stream stage was not uniform between hydrometric stations. While discharge measurements were made for both upstream and downstream locations, the rapid fluctuations in the downstream discharge measurements and the fact that upstream and downstream measurements were not taken at the same time rendered these measurements unreliable. An attempt to estimate streamflow from stream stage proved unsuccessful.
Streamflow depletion during the pumping test was modeled using a suite of available analytical solutions. The models converge at late time (except the Michigan screening tool) attaining 95% normalized streamflow depletion around 750 days. Analysis of the field data highlighted the importance of accurately characterizing the hydraulic properties of the streambed sediments. Varying the streambed hydraulic conductivity and thickness showed that small changes in the streambed leakance parameter result in significant changes in the estimated rate of streamflow depletion in all streamflow impedance models. Analysis of field data highlighted the importance of properly designing and implementing the field test. This includes a more detailed examination of the seasonal variation in hydraulic connectivity, conducting the pumping test during baseflow conditions, and measuring streamflow outside the radius of influence of the pumping well to ensure the full impact is captured.
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Report Type
Subject
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Region - Lower Mainland |
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Watershed Groups - 100 - Fraser |
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Water Information - Groundwater |
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