Seasonal soil water dynamics in the jarrah forest, Western Australia. I: Results from a hillslope transect with coarse‐textured soil profiles

Abstract Seasonal soil water dynamics were measured on a hillslope transect in the jarrah forest of southwest Western Australia over the period 1984‐86 using mercury manometer tensiometers, gypsum blocks, and a neutron moisture meter. The soil water potential gradients indicated downward vertical drainage flux through winter and spring. There was generally a change to an upwards flux in early summer which was sustained through to autumn. A shallow ephemeral saturation zone was identified in and above a duricrust layer, lasting up to three days after heavy, late winter rainfall. The annual maximum to minimum unsaturated soil water storage on the hillslope was approximately 400 mm to 6 m depth and 480 mm to 15 m depth. This did not change significantly in years of substantially different winter rainfall. The magnitude of seasonal soil water storage was similar to other forested areas with deep soil profiles. The depth of observable infiltration was dependent on annual rainfall. This was consistent with the observation that groundwater levels responded to rainfall over the whole hillslope in wet years but only responded on the lower slopes in dry years. The average summer drying rate of the soil profile to 6 m depth of 3.5 mm day−1 was within the range of values reported for forests elsewhere. In late summer, following an extended drought period, the drying rate decreased downslope but increased midslope.