A comparison of streamflow, salt and water balances in adjacent farmland and forest catchments in south-western Victoria, Australia

© 2014 John Wiley & Sons, Ltd. A study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south-western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20-month study period. Monthly streamflow was always greater in the pasture-dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture-based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average (1954-2012) summer rainfall. Streamflow peaks in the plantation-based catchment were smaller than in the pasture-dominated system. Flow duration curves show differences between the pasture and plantation-dominated catchments and affect both high-flow and low-flow periods. Groundwater levels fell (up to 4.4m) in the plantation catchment during the study period but rose (up to 3.2m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south-eastern Australia, but this benefit is offset by reduced total streamflow.