Land use effects on sediment yields and soil loss rates in small basins of Triassic sandstone near Sydney, NSW, Australia

Abstract

Sedimentation surveys of dams in small sandstone drainage basins near Sydney, Australia, demonstrate that land use is the dominant factor determining sediment yields and soil loss rates. Cultivated basins produce an average sediment yield of 7.1 t/ha/year whereas grazed pasture and forest/woodland basins export averages of only 3.3 and 3.1 t/ha/year, respectively. Nevertheless, these yields are high by Australian standards. Sediment exports from grazed pasture and forest/woodland basins are similar because the forest/woodland basins are also grazed. Dam sediments are enriched in clay and organic matter in comparison to topsoils. Gullies and bank erosion are not active geomorphic processes in the drainage basins investigated so that the measured sediment yields could be validly compared to soil loss rates determined by empirical soil loss equations, Modified Universal Soil Loss Equation (MUSLE), Soiloss and Revised Universal Soil Loss Equation (RUSLE), which do not account for gully and channel erosion. These equations accurately predicted the measured sediment yields, with MUSLE being the most accurate. Although Soiloss is the only empirical equation to use Australian data, MUSLE performed marginally better, despite being a simplified version of the Universal Soil Loss Equation (USLE) that is used for teaching. RUSLE predictions of soil loss rates were also closely correlated with measured sediment yields.