seven-year water balance study of an evapotranspiration landfill cover varying in slope for semiarid regions

The goal of radioactive and hazardous waste disposal in shallow landfills is to reduce risk to human health and to the environment by isolating contaminants until they no longer pose a hazard. To achieve this for a semiarid region, we studied a landfill cover containing a gravel layer, an evapotranspiration (ET) cover, in the field for 7 yr. We measured total water balance at 6-h intervals for this landfill cover design in four 1.0- by 10.0-m plots with downhill slopes of 5, 10, 15, and 25%. During the 7 yr of the field study, runoff accounted for 1.4 to 3.8% of the precipitation losses on these unvegetated landfill cover designs, whereas similar values for evaporation ranged from 88 to 95%. Evaporation usually increased with increases in slope in our field plots; for example, the ET Cover at slopes of 5 and 15% displayed 274 and 296 cm of evaporation, respectively. Interflow and seepage usually decreased with increasing slope; for example, as slope increased from 10 to 25%, interflow decreased from 18.4 to 8.8 cm. Seepage consisted of up to 1.7% of the precipitation on the ET cover, showing a maximum value of 5.3 cm on the ET cover with the slope of 5%.