Infiltration under Confined Air Conditions: Impact of Inclined Soil Surface

Abstract

Core Ideas A non‐flat surface geometry may lead to preferential release of confined air. There is a clear difference in the air‐pressure dynamics in an inclined soil surface. The infiltration rate increased for an inclined surface by about 50%. Entrapped air effects on infiltration under ponding condition are important in many engineered systems such as soil aquifer treatment and managed aquifer recharge. Earlier studies found that under ponding conditions, air is compressed until it reaches a pressure that enables it to be released, typically by intermittent bubbling through the surface. Entrapped air can reduce infiltration by 70 to 90%. Previous studies considered a flat soil surface topography and mostly vertical one‐dimensional flow. The objective of this study was to investigate the effect of irregular, inclined surface topography on infiltration, hypothesizing that non‐flat surface geometry may lead to preferential release of the confined air and subsequently increase infiltration. In a series of column experiments, we investigated the infiltration rates of flat and inclined soil surfaces. Our results indicate a clear infiltration rate increase of about 50% for an inclined surface. Further, we observed a clear difference in the air‐pressure dynamics, indicating that under an inclined surface, air is being released continuously, while under flat surface conditions, air is being released intermittently. This behavior is explained by differences in the air‐breaking and air‐closing values across the soil column, while the air pressure is practically uniform beneath the wetting front.