Observation of water and solute movement in a saline, bare soil, groundwater seepage area, Western Australia. Part 2. Annual water and solute balances

Abstract

Intensive hydrological and meteorological observations were used over 2 years at a small, salinised, bare soil, groundwater seepage area in Western Australia to determine annual water and solute balances and the processes mobilising and discharging saline groundwater. The study area of 40 m by 40 m comprised a two-layered (duplex) soil, with an upper permeable layer 0.3–0.4 m thick and a less permeable underlying layer. During the wet winter season, groundwater discharge from the study area corresponded to ~45% of the rainfall amount. The annual salt discharge from the area via groundwater flow was calculated to be ~2.1 kg/m2 as NaCl, which was almost the same as the salt mass stored in the upper layer in summer. A salt-discharge model was developed and showed that even though the bare soil, groundwater seepage area occupies only a few per cent of the total catchment area, the salt discharge from it was a large component of that from the total area. During the dry summer season, lateral groundwater flow did not occur. Rainfall that recharged and became stored water in the previous winter became the source of evaporation in the following summer, with 60–70% of the evaporated water in summer derived from stored water of the previous winter.