Evaluating the Influence of Vegetation on Evapotranspiration from Waste Rock Surfaces in the Elk Valley, British Columbia

Abstract

Coal mines operated by Teck Coal Ltd., in the Elk Valley, British Columbia, utilize the method of surface mining, resulting in large waste rock piles that affect water quality. In order to limit the influence that these waste rock piles have on water-rock interaction, alternate management strategies are being explored. In this study, the influence of vegetation on evapotranspiration is examined, as potential benefits exist in using vegetation to reduce the infiltration and percolation of water into waste rock. During the 2013 growing season, energy and water balance components were measured using the eddy covariance technique at a bare waste rock surface, a waste rock surface with a vegetated grass cover, and a waste rock surface with a reclaimed forest cover. In addition, other water balance components were measured, such as soil water storage and precipitation. The placement of vegetation atop the waste rock pile allowed for increased evapotranspiration compared to the bare waste rock surface. From 23 May 2013 to 30 September 2013, the reclaimed forest and reclaimed grasses site experienced 305 mm and 272 mm of ET, respectively, while the bare waste rock site had only 140 mm of ET. This increase in evapotranspiration suggests less deep percolation at vegetated sites, estimated as 148 mm, 172 mm and 246 mm for the grass, forest and bare rock sites respectively. ET at the vegetated sites was dominantly controlled by the net radiation, while the near surface moisture was the dominant control on ET at the bare rock site. Results from this study suggest future reclamation projects should consider placing surface vegetation as a potential method to reduce deep percolation into waste rock piles.