Modelling sediment and nutrient budgets in the Lake Burragong catchment: Report to the Sydney Catchment Authority

[摘要] This study has applied the SedNet catchment sediment and nutrient budget model to the Lake Burragorang catchment to provide predictions about the source areas and processes responsible for generating the sediment delivered to Lake Burragorang over the last few decades (circa 1980 – 2000). Five model scenarios have been evaluated for their capacity to match three independent data sets from the catchment including: 1. suspended sediment loads estimated at gauging stations, 2. geochemical tracer data measuring the relative sediment contributions at river confluences, 3. geochemical tracer data measuring the relative contribution of surface versus sub-soil sediment sources. Of the five models, models A and B which retained the Revised Universal Soil Loss Equation predictions for hillslope erosion across the entire catchment performed relatively poorly. Models C, D and E, which for forested areas adopted an increased rate of sediment delivery (in line with gauging station sediment load estimates) performed better. The model that most closely represented the observational data from the catchment (model E) had as its main feature a relatively high (40 t/km2/yr) rate of sediment yield from forested hillslopes for sub-catchments near the reservoir, along with reduced rates of contemporary sediment supply from gully erosion. Both of these characteristics were drawn from independent studies of the catchment. However, there is likely to be important intra-catchment variation in both hillslope and gully erosion processes that is not resolved in the current modelling and this represents an area in which future research could profitably focus upon. The model E parameterisation predicts that 240 kt/yr of fine sediment is delivered to the reservoir. The vast majority of this sediment is predicted to be sourced from hillslope erosion in sub-catchments relatively close to the reservoir. Gully erosion is the next most significant sediment source. If the contributions from the majority-forested sub-catchments are disregarded, suspended sediment delivery to the reservoir is predicted to be dominated by the agricultural sub-catchments below Lyell Dam on the Coxs River and also from sub-catchments draining to the Wollondilly River between Paddys River and Guineacor Creek. Other notable source areas include much of the Tarlo River sub-catchment. The Mulwaree River, much of the upper Wingecarribee River and the Coxs River above Lyell Dam are predicted to contribute low rates of suspended sediment to the reservoir.

[发布机构] CSIRO

[学科分类] 地球科学(综合)