Ground water-surface water relations in the Flathead River valley near the proposed Cabin Creek Coal Mine, British Columbia, Canada

Moreland, Joe; Liebscher, Hugh; Van Voast, Wayne; Feltls, R

The area of the proposed Cabin Creek coal mine was studied to obtaininformation needed to respond to questions posed by the InternationalJoint Commission advisors concerning water resources near the internationalborder. Specific interest focused on determining the extent andcharacter of surficial material in the Flathead River valley, identifyinggaining and losing reaches of the river and major tributaries, anddocumenting ambient water quality at selected sites. Quaternary alluvial streambed deposits consisting of clean sand,gravel, and boulders underlie the valleys of the Flathead River and majortributaries. Thickness of the alluvial deposits depends on depth tounderlying Quaternary glacial deposits or Tertiary bedrock. The alluvialdeposits in the Flathead River valley thin to a veneer of cobbles nearthe mouth of Couldrey Creek. Measurements of streamflow at 20 sites in the Flathead River valleyindicate that water discharges from the alluvial deposits to most of thetributaries and to the river near the proposed mine. The Flathead Rivergained 0.87 cubic meter per second (31 cubic feet per second) of flownear Howell Creek. The Flathead River and Couldrey Creek gained about0.81 cubic meter per second (28.5 cubic feet per second) of flow near themouth of Couldrey Creek where bedrock crops out in the streambeds. Bedrockoutcrops effectively interrupt the alluvial aquifer system betweenthe proposed mine site and the international border. The Flathead Riverlost 0.87 cubic meter per second (31 cubic feet per second) of flowbetween the bedrock outcrops and the international border; this streamflowloss enters alluvial deposits and flows across the internationalborder as subsurface flow. Analysis of samples from 18 stream sites and 1 spring site indicatesgeneral trends in water quality. In Howell Creek, concentrations of calcium,magnesium, and sulfate increased slightly downstream. Conversely,samples from Sage and Couldrey Creeks indicate downstream increases inconcentrations of calcium, magnesium, and alkalinity, but decreases inconcentrations of sulfate. Water quality of Cabin Creek was relativelystable through the sampled reach. Decreased concentrations of calcium andalkalinity in the Flathead River reflect the effect of inflow from CouldreyCreek and the ground-water inflow documented by streamflow measurements.

Ground water-surface water relations in the Flathead River valley near the proposed Cabin Creek Coal Mine, British Columbia, Canada

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