Developing a sediment budget for a small drainage basin in Australia

A sediment budget was developed for the 1.7 km2 Maluna Creek drainage basin located in the Hunter Valley, New South Wales, Australia, for the period 1971‐86. the impact of viticulture, which commenced at Maluna in 1971, was studied using erosion plots, with caesium‐137 as an indicator of both soil erosion and sedimentation. Two methods were used to estimate vineyard soil losses from caesium‐137 measurements. Sediment output from the catchment was measured for three years, and extrapolated from readings taken at a nearby long‐term stream flow gauging station for the remaining 13 years. Relative amounts of soil loss from forest (60 per cent basin area), grazing land (30 per cent) and vineyards (10 per cent) were calculated. Soil losses by rain splash detachment were ten times greater from bare/cultivated sufaces than from the forest. Erosion plots of area 2 m2 showed no significant differences in soil loss between forest and grassland but, under bare soil, losses were 100 times greater. the 137Cs method was employed to calculate net soil loss from all vineyard blocks using both a previously established calibration curve and a proportional model. the latter method gave estimates of soil loss which were 3‐9 times greater than by the calibration curve, and indicated that average soil losses from the vineyard were equivalent to 62 t ha−1 y−1 (1971‐86). It was estimated that the forest contributed 1‐8 per cent, the grazing land 1.6 per cent, and the vineyard 96.6 per cent of the total soil loss during that period. Sediment storages within the fluvial system adjacent to the vineyard ws 9460 t for the period, whereas sediment output was equivalent to 215 t km−1 y−1. Independent measurements of soil erosion, storage, and output showed that 56 per cent of the eroded sediment remained in the catchment, and 34 per cent was transported out by Maluna Creek. the budget was able to be balanced to within 10 per cent.