Interpreting sediment delivery processes using suspended sediment‐discharge hysteresis patterns from nested upland catchments, south‐eastern Australia

Abstract

AbstractIn this study, suspended sediment concentration (SSC) and discharge (Q) hysteresis patterns recorded at the outlets of two nested upland catchments in south‐eastern Australia were examined. Detailed monitoring of sediment flux was undertaken in a 1·64 km2 sub‐catchment located within a 53·5 km2 catchment for which sediment yield was measured and the extent of incised channels mapped. The analysis of SSC–Q hysteresis patterns was supplemented by these additional datasets to contribute to the explanation of observed patterns. Clockwise SSC–Q hysteresis loops (with the suspended sediment peak leading the discharge peak) were recorded most frequently at both sites. This was attributed to initial rapid delivery of sediment from channel banks, the dominant sediment source in the sub‐catchment and probably also for the catchment, in conjunction with remobilization of in‐channel fine sediment deposits. Sediment exhaustion effects were considered to enhance clockwise hysteresis, with reduced SSC on the falling limb of event hydrographs. Pronounced exhaustion effects were observed on some multi‐rise events, with subsequent flow peaks associated with much reduced sediment peaks. To compare SSC–Q hysteresis patterns between the two catchments, a dimensionless similarity function (SF) was derived to differentiate paired‐event hysteresis patterns according to the extent of pattern similarity. This analysis, coupled with the other datasets, provided insight into the function of erosion and sediment delivery processes across the spatial scales examined and indicated the dependency of between‐scale suspended sediment transfer on defined flow event scenarios. Quantitative measures of event SSC–Q hysteresis pattern similarity may provide a mechanism for linking the timing and magnitude of process response across spatial scales. This may offer useful insights into the between‐scale linkage of dominant processes and the extent of downstream suspended sediment delivery. Copyright © 2009 John Wiley & Sons, Ltd.