Evaporation from a waste-rock surface, Key Lake, Saskatchewan

Abstract

An accurate evaluation of the water balance and net percolation through mine waste-rock piles is critical to the development of decommissioning plans for these wastes. One of the most difficult components of the water balance to quantify is evaporation. Evaporation and the surface energy balance were directly measured from a fine- to medium-grained sand waste-rock pile near Key Lake, Saskatchewan, Canada between 6 June and 25 August 2002 using the eddy covariance method. Actual evaporation for the 81 day study period was 145 mm, which was significantly less than both a potential evaporation of 247 mm and rainfall of 236 mm during this period. The waste-rock pile had a distinct radiation and energy balance as high surface albedo reduced available energy for evaporation. The greatest fraction of daytime available energy was partitioned into latent heat, followed by soil heat flux, and sensible heat flux, respectively. The Bowen ratio averaged 0.45 ± 0.10 for the entire study period. A simple actual evapotranspiration model, which is an extension of Penman and consistent with the complementary approach, was used to simulate evaporation atop the pile. Model results indicate 134 mm of evaporation for the study period and agree well with observations.Key words: evaporation, waste-rock, energy balance, eddy covariance, acid rock drainage.