The Water Deficit of Evapotranspiration Covers on Potash Tailing Piles Using CropWat

Evapotranspiration covers are key to minimizing water percolation in waste systems. On potash tailings piles, evapotranspiration covers are important because they may decrease the leaching of brines generated from precipitation erosion. Considering this, the water deficit of four different potash tailings piles covering materials were evaluated using the CropWat model. This study was based on a lysimeter experiment carried out in Heringen, Germany. The experiment consisted of 4 different technogenic substrates made of municipal incineration wastes and coal combustion residues covered with a mixture of perennial grasses. By using the FAO CropWat model, the effective precipitation, crop evapotranspiration, actual evapotranspiration and the water deficit were estimated from 2014 to 2016. Further simulations determined the water deficit under different precipitation probabilities, 20, 50 and 80 %, and crop coefficients, varying from 0.4 to 1.0. CropWat estimated a crop evapotranspiration of 641.9 mm/year and an actual evapotranspiration of 448.3 mm/year or 68.5 % of the annual ground-level precipitation. Over three calendar years there was a mean estimated water deficit of 28.7 %. Higher levels of water deficit were estimated in spring and summer months. Further simulations revealed the water deficit may range from 55.0 mm (8.7 %) for high precipitation levels to 157.4 mm (24.8 %) for low precipitation depths. Additionally, water deficit is associated with the crop coefficient, ranging from 0.0 mm using a constant crop coefficient of 0.4 to 105.3 mm using a constant crop coefficient of 1.0 for an average precipitation. Overall, the CropWat model agreed with the observed measurements and no large differences among the substrates was verified.