Development of unstable flow and reduced hydraulic conductivity due to water repellence and restricted drainage
Hardie, M and Deurer, M and Doyle, R and Lisson, S and Cotching, WE and Mattern, K, Development of unstable flow and reduced hydraulic conductivity due to water repellence and restricted drainage, Vadose Zone Journal, 11, (4) pp. 1-11. ISSN 1539-1663 (2012) [Refereed Article]
The effect of water repellence and antecedent soil moisture on wetting front stability and infiltration rate are reported for a seasonally water repellent topsoil. The effect of water repellence on infiltration was determined by comparing the in situ infiltration of water to that of a 7M ethanol solution. Wetting front stability was measured during infiltration of water into
repacked, wettable and water repellent soils, within a Hele-Shaw chamber. Water repellence restricted in situ movement of water through large macropores (>500 μm), which decreased intrinsic permeability by 1 to 2 orders of magnitude. In repacked soils, water repellence caused the development of unstable wetting fronts and reduced infiltration from 240 mm h-1 to 101.7 mm h-1. Infiltration into wettable soils at moisture contents near field capacity was expected to result in rapid infiltration and stable wetting fronts. However in repacked
soils, wetting front instability developed, and infiltration rates were 190% lower when air and/or water movement through the base of the chamber was restricted. Infiltration into in situ soil was also slower at high antecedent soil moisture. The hydraulic conductivity of the 7M ethanol solution decreased significantly from 112.3 mm h-1 in dry water repellent conditions,
to 35.6 mm h-1 in wettable soils at high antecedent moisture contents. Consequently the previously reported development of wetting front instability and reduced infiltration into in situ wettable soils at high moisture contents were confirmed and attributed to difficulty displacing existing soil water during infiltration of new water.