British Columbia Mine Reclamation Symposium

Near-surface water balances of waste rock dumps Birkham, T.; O'Kane, Mike; Goodbrand, Amy; Barbour, S. Lee; Carey, S. K.; Straker, Justin; Baker, Trevor; Klein, Rupert


The near-surface water balance of mine impacted landscapes is a key control on re-vegetation performance, and on the hydrologic and water quality impact at the watershed scale. As part of Teck Resources Limited’s applied research and development program focused on managing water quality in mine-affected watersheds, 12 sites representing a range of waste rock dump reclamation surface management options (i.e. soil cover, surficial mounding) were instrumented in 2012 to measure meteorological and soil water response and to quantify the near-surface water balances with a focal objective to improve estimates of ranges of net percolation into waste rock dumps under a range of scenarios. Subsurface water and meteorological conditions varied substantially, as expected for the range of elevation, slope aspects, vegetation, soil covers, geographic location and surface preparation of the selected sites. Patterns in water balance trends emerged in the first year of analysis with net percolation (NP) into underlying waste rock typically decreasing for increased vegetation and soil cover, as well as for decreases in rainfall or snowmelt. Increased vegetation cover resulted in a greater volume of water removed from near-surface through evapotranspiration. The lowest NP (as % of water input) was estimated for a mature, reclaimed conifer forest site and a dense agronomic grass/alfalfa covered site. Net percolation estimated for a soil covered waste rock slope was approximately 15% (of water inputs) less than an adjacent bare waste rock slope. Decreased NP was partly attributed to greater water storage in the finer-textured soil cover. Net percolation through the soil cover is expected to further decrease with time as vegetation establishes relative to the bare waste rock slope. Net percolation for a mounded, bare waste rock slope was less than estimated for an adjacent smooth slope. Net percolation below a trough was similar to the smooth slope, but decreased at the crest and mounded mid-slope positions due to thinner snowpack (less snowmelt) from wind scouring. Additional monitoring and analysis of site-specific water balances will help define the shift in the relative proportions of water entering the deposits as vegetation matures.

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