Determination of Evaporation from a Tailings Storage Facility Using Field Measurements and Satellite Observations

Most mining operations produce waste material, or tailings, which is commonly stored within impoundments known as tailings storage facilities (TSFs). A common TSF design involves depositing slurry on tailings ‘beaches’ which are sloped towards a containing wall or central pond which collects excess water. A crucial aspect of safely operating TSFs is managing the residual moisture content of the deposited tailings, which requires an accurate understanding of the water balance of the TSF. However, evaporation from a TSF is particularly hard to quantify as the degree of surface wetness varies spatially and temporally, and moisture content depends on the time since tailings deposition and the prevailing climate. This study addresses these issues at an active TSF by combining field measurements, models, and satellite observations. Evaporation from open water was measured using a floating evaporation pan and evaporation from the tailings beaches was investigated using micro-lysimeter measurements. Evaporation rates for different moisture contents were expressed as a fraction of open water evaporation and a strong relationship was developed for use in satellite analysis. Spatial and temporal patterns of open water and moisture content were determined at 20 m resolution using moisture indices applied to Sentinel-2 satellite scenes. Continuous open water evaporation rates and spatial moisture content information were combined to estimate total TSF evaporation. Comparison of TSF evaporation rates to those derived using an existing site water balance model showed very good agreement. The methodology developed could be applied at other locations around the world.