Doctor of Philosophy
School of Earth and Environmental Sciences
Simms, A. D., Formulating and testing a distributed, empirically-based soil loss model, OzMUSLE, using soil remobilisation and sedimentation studies, Doctor of Philosophy thesis, School of Earth and Environmental Sciences, University of Wollongong, 2007. http://ro.uow.edu.au/theses/2927
Soil erosion is a significant environmental issue in southeastern Australia. This research has involved formulating and testing an empirically-based soil loss model, OzMUSLE, as a tool for soil erosion assessment and management. OzMUSLE is a raster-based Geographical Information System (GIS) version of the Universal Soil Loss Equation (USLE), modified to incorporate temporal and spatial variation in coastal catchments of the Sydney Basin. Initial parameterisation was undertaken in the catchment of Lake Wollumboola, a coastal lagoon. Further modelling was performed for the Cordeaux catchment, a small headwater catchment, with steep-sided valleys, that has been dammed within the metropolitan special areas of the sandstone-dominated Sydney Catchment. These field sites were chosen as representative of catchments in southeastern NSW that do not have extensive floodplains but have relatively undisturbed vegetation cover. Although the original USLE/RUSLE model was developed to estimate erosion on plots that were uniform in relation to soil and land cover, the concepts have been adapted to extrapolate the approach to hillslopes and catchments, which are not uniform. Variations in upslope runoff on erosion were explicitly considered and incorporated. OzMUSLE soil loss modelling indicates that net soil erosion is more likely to occur after 20-year (or more) average recurrence interval (ARI) events on sandstone, but with events greater than 10-year ARI on siltstone. Modelled event-based sediment yields vary in a similar way and are within the estimates for similar catchments in Australia. Annual rates of soil loss for Wollumboola, ranging from 0 to 15 t ha-1yr-1, with a mean of 0.46 t ha-1yr-1 for the year 2002, and Cordeaux, ranging from 0 to 8.23 t ha-1yr-1, with a mean of 0.17 t ha-1yr-1 for 1983-2003, are insignificant to low in relation to soil formation rates. Patterns of soil loss were detected using caesium-137 (137Cs) indicate that areas experiencing net erosion in Wollumboola catchment are located mainly along mid-slopes or are disturbed, with limited deposition on lower sections of slopes. In the Cordeaux catchment, a six-element 137Cs-sediment hillslope model indicates that on average claystone slopes contribute four times more sediment than sandstone slopes to the stream network. Sedimentation studies, using excess lead-210 (210Pbex) in lake-bed cores, indicate that sediment yield during the past 69 to 70 years, from the catchments of Lake Wollumboola and the Cordeaux reservoir, ranges from 0.37 to 1.21 t ha-1yr-1, with an average of 0.63 t ha-1yr-1. Modelled amounts of sediment delivered to the outlets of streams are within the same order of magnitude as measured sediment yields. However, OzMUSLE is not substantiated by observed specific sediment yield, implying that, in its current form, the new model might not be a useful tool for assessing sediment delivery at the catchment scale until further refinements and testing are carried out.
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