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Report: Mapping aquifer stress, groundwater recharge, groundwater use, and the contribution of groundwater to environmental flows for unconfined aquifers across British Columbia

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Groundwater is a critical source of freshwater supporting residential, commercial, industrial and agricultural sectors within British Columbia. This report derives aquifer-scale estimates of groundwater withdrawal, recharge, and groundwater's contribution to environmental flows as a means to provide screening level estimates of aquifer-scale stress using the groundwater footprint. Results suggest one in every five unconfined aquifers in the province is likely stressed.

Author:  Tara Forstner, Tom Gleeson, Leigh Borrett, Diana M. Allen, Mike Wei, Andarge Baye

Date Published:  Aug 2018

Report ID:  54468

Audience:  Government and Public

This report estimates groundwater use across B.C. for all the major groundwater use sectors and maps this groundwater use for each aquifer in the province for the first time. Data on major sectors of use was synthesized from provincial and national sources and spatially downscaled and interpolated to derive groundwater use volumes for currently mapped aquifers. Groundwater use was first classified based on means of distribution either through a municipal water distribution systems or self-supplied through private wells, and secondly, by major groundwater use sectors namely, domestic, commercial, industrial, irrigated agriculture, and finfish aquaculture. The methodologies used in deriving the spatially distributed groundwater use volumes are different for each sector based on the data availability and scale of reporting. Results suggest that British Columbia uses a total of ~ 562 million cubic metres of groundwater annually. The largest annual groundwater use by major sectors are agriculture (38%), finfish aquaculture (21%), industrial (16%), municipal water distribution systems (15%), and domestic private well users (11%). This study is a preliminary assessment, as the majority of the groundwater volumes were unreported per sector, and therefore, different methodologies are used to interpolate available data. Recharge is estimated using two approaches; a generalized aquifer-scale method, using the Hydrologic Evaluation of Landfill Performance (HELP) and modelled recharge outputs from PCR-GLOBWB, a global hydrologic model. Results show that generally recharge predictably varies with precipitation and that the average recharge is 462 mm (32% of precipitation) for the aquifer-scale HELP method and 393 mm (33%) for the global hydrologic model. The generalized methodology results in annual recharge rates that are consistent with the more localized studies of the Abbotsford-Sumas aquifer in humid southwestern B.C. and the Grand Forks aquifer in semi-arid south-central B.C.. Although the results are consistent with previous localized recharge modelling, as well as expected patterns of recharge across the province, these recharge estimates should only be used for regional to provincial scale groundwater resource management rather than localized analysis. For each aquifer, the groundwater footprint (expressed as the unitless ratio of groundwater footprint to aquifer area or GF/A) is calculated four times; using results from each of the two methods used to estimate recharge and each of the two methods used to estimate the groundwater contribution to environmental flows. None of the methods can be categorically considered more scientifically robust, so all four of the calculated groundwater footprints are reported and combined into three mapped categories that also highlight the uncertainty of the results: (a) more stressed (highly certain) if all results suggest aquifer stress; (b) more stressed (less certain) if some results suggest aquifer stress; (c) less stressed if none of the results suggest aquifer stress. The groundwater footprint, which is an indicator of groundwater stress with a single cut-off: GF/A > 1 suggests an aquifer is more stressed, and GF/A < 1 suggests less stressed. There is no scientific basis to interpret the calculated values more finely. Given the significant limitations and uncertainties in the input parameters and single cut-off, the calculated values of the groundwater footprint should not be over-interpreted. For example, aquifers with GF/A of 2 or 10 should both be considered 'more stressed' and provoke similar management decisions. Of the unconfined aquifers (n = 404) in the province, 43 aquifers (11%) are stressed with high certainty, 32 aquifers (8%) are stressed with low certainty, 296 aquifers (70%) are less stressed, and 29 aquifers (11%) were not included due to missing parameters or issues where modelled recharge was less than environmental flows.

Report Type
  Biogeoclimatic Zone - AT Alpine Tundra
  Biogeoclimatic Zone - BG Bunchgrass Zone
  Biogeoclimatic Zone - BWBS Boreal White and Black Spruce Zone
  Biogeoclimatic Zone - CDF Coastal Douglas-fir Zone
  Biogeoclimatic Zone - CWH Coastal Western Hemlock Zone
  Biogeoclimatic Zone - ESSF Engelmann Spruce - Subalpine Fir Zone
  Biogeoclimatic Zone - IDF Interior Douglas-fir Zone
  Biogeoclimatic Zone - PP Ponderosa Pine Zone
  Biogeoclimatic Zone - SBPS Sub-Boreal Pine - Spruce Zone
  Biogeoclimatic Zone - SBS Sub-Boreal Spruce Zone
  Biogeoclimatic Zone - SWB Spruce - Willow - Birch Zone
  Region - Province Wide

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