Effect of an Asphalt Barrier on Water Storage and Drought Probability1

Abstract

AbstractField measurements of water redistribution after infiltration were made on two sandy soils with and without asphalt barriers at a 55 cm depth to determine the barrier effect on soil water potential gradients and on water retention at various times. Estimates of the effect of the barrier on seasonal drought severity and on movement of water to horizons below the barrier were made on one of the soils.Soil water potential gradients and the volumetric water content at different depths were nearly the same for barrier and nonbarrier plots on Hubbard loamy coarse sand because a coarse sand‐gravel layer between the 25 and 50‐cm soil depths acts as a water barrier. After 96 hours drainage, suctions in Zimmerman fine sand reached 31 cm of water just above the barrier and 61 cm at the same depth without barrier. Available water to barrier depth was increased from 2.9 cm to 7.5 cm by the barrier.Available water above the barrier was determined for Zimmerman fine sand and was used to calculate the effect of a barrier on drought probability. This analysis showed that on barrier plots, there would be 25 fewer drought days in the driest year in 10, and 31 fewer in the 5 driest years in 10.Based on rainfall at the Zimmerman fine sand site, it was shown that, over a 3‐year period, supplemental water needed to keep an active growing crop could have been reduced by 58% with a barrier. Probable water loss by percolation, on the other hand, would have been one‐fifth as great with a barrier as without.