Sensitivity of protective barrier performance to changes in rainfall rate

摘要

Single-or multi-layered surface barners are used for protecting the underlying hazardous or radioactive waste storage facility and for reducing the risk of dispersion of contaminants to the ground water. To assess the effect of variations in net rainfall rate (total rainfall minus evapotranspiration) on the hydraulic response of a multi-layered barrier, a series of flow simulations were performed. Water fluxes in different layers of the barrier were numerically calculated for three net rainfall rates, i.e. 0.0255, 0.0742, and 0.141 cm/day. These rates correspond to dry, average, and wet climatological conditions in Beigium. Results show that for dry condi- tions, almost 45/100 of the water infiltrating the top of the barrier is laterally evacuated. When the net rainfall rate increases from 0.0255 to 0.0742 cm/day, more water is being laterally diverted, and only 22/100 of the applied rainfall percolates through the barrier. If the rainfall rate is increased from 0.0255 to 0.141cm/day, the percolation becomes 14/100 of the applied rainfall. This indicates that fluxes leaving the bottom of the repository increase only slightly, although the rainfall rate for wet conditions is approximately 5 times larger than for dry conditions. Under dry conditions a slightly negative pressure develops in the bottom of the low-perme- ability clay layer. However, this desaturation does not affoct the integrity of the clay.