Unsaturated flow simulations through the multi-layer cover of the near surface disposal facility for category a waste at Dessel.

This report describes two-dimensional unsaturated flow simulations in the earth cover of the near-surface waste disposal facility for category A waste at Dessel, Belgium. The geometry of the earth cover was based on the design of March 2009. Calculations are done in a conceptual model of the earth cover with respect to the dimensions and the material distribution. Boundary conditions are simplified to steady-state net infiltration rates and a few cases considering periods of extreme rainfall. Water flow simulations show that the sand layer on top of the low-permeable clay layer is the main location for lateral water drainage. About 15% of the net infiltration drains below the clay layers. The simulations with the extreme rainfall events show that: (i) the sand layer just above the clay layer becomes saturated and the extent of the zone of saturation increases with increasing duration of the rainfall event, and (ii) the water saturation increases in the top layers in proportion to the rainfall intensity, i.e. the higher the intensity of the rainfall during the extreme rainfall event, the higher the water saturation.