A novel technique for estimating wetting front migration rates through the vadose zone based on changes in groundwater velocity

Managed aquifer recharge in unconfined aquifers often requires careful monitoring of infiltration rates to optimize residence times in the unsaturated zone to enhance biodegradation and to identify clogging. Conventional methods of monitoring infiltration performance commonly rely on interpreting changes in soil moisture or changes in water table elevation using in situ devices. This paper describes a novel technique based on changes in groundwater velocity near the infiltration zone. Two field experiments were conducted that involved imposing step increases in the rate of recharge to a sandy, 10 m thick vadose zone, following cessation of infiltration over several days and different pre-existing soil moisture conditions. Estimated wetting front migration rates were comparable for the groundwater velocity (7.7 m day−1), water table elevation (7.3 m day−1) and soil moisture (8.0 m day−1) techniques investigated. Further work is required to validate the groundwater velocity technique at other field sites, and extend its use, e.g. to optimize infiltration rates and identify vadose zone clogging.