A study of soil erosion on vertisols of the eastern Darling Downs, Queensland .II. The effect of soil, rainfall, and flow conditions on suspended sediment losses

Abstract

Runoff water was sampled as it discharged through weirs installed at the outlet of 1 ha contour bay catchments. Cover, rainfall intensity, and soil tilth were important factors determining the concentration of suspended sediment in runoff. Mean delivery ratios for a grey clay, and a black earth, were 0.19 and 0.13 respectively. Contour banks reduced sediment loads reaching the bottom of slopes by at least six-fold. Three methods of calculation of total sediment loss were assessed. It was found that a flow-weighted mean of rising stage samples, and the arithmetic mean of sequential samples, were adequate in most cases for determining sediment losses. However, sequential samples weighted for discharge between samples were necessary for reliable measurements, especially during complex events.