Estimating the nature, timing, and depth of preferential flow in a texture-contrast soil

Occurrence of preferential flow in soil is known to increase the risk of off-site agrochemical mobilisation to groundwater and waterways. This study investigated the ability of a commercially available soil moisture probe to determine the timing, depth and magnitude of preferential flow events in a texture-contrast soil. Occurrence of preferential flow was not related to rainfall magnitude nor rainfall intensity, rather preferential flow occurred when antecedent soil moisture was below 70-76 % of total soil moisture. High frequency soil moisture monitoring over a 21 month period was able to determine the timing, depth and wetting front velocity of preferential flow events. However the spatial variability of the preferential flow paths meant that two to three soil moisture probes were required to determine changes in soil moisture or the preferential flow flux.