Catchment Management for Improved Water Quality
Abstract
For good regional planning of water quality issues there is a need to relate the impacts of sediment and nutrients on water quality to their sources. Clearly, there are insufficient resources to adequately manage sediment and nutrient movements across entire landscapes. Catchments cleared of native vegetation have an increased susceptibility to erosion, but the risks vary markedly both within and between catchments. Given the scale of the overall problem it is important to prioritise management works to areas where limited efforts will have a positive impact. The project described here identified patterns of sediment transport within the Glenelg River basin in western Victoria, Australia. The project assessed:
-
the relative contributions of sediment and nutrient supply to rivers from hillslope, gully and streambank erosion;
-
the suspended sediment and nutrient loads of the river;
-
sediment and nutrient delivery to the end-of-valley; and
-
the extent of sediment slugs formed by increased bedload transport.
The project relied on a computerised model (SedNet) of the catchment’s sediment budget to predict the spatial patterns of sediment source, transport and deposition. Application of SedNet contributes to our understanding of broader river health issues and water quality management by integrating a wide range of input information to assess the current sediment and nutrient loads of rivers.
There are limited data in Australia that describe erosion rates and river sediment loads. Fortunately, however, we have a good understanding of sediment transport processes, and ample data to describe the factors that control these processes (stream gauging records, digital elevation models, rainfall records, and remote sensing of land cover). SedNet incorporates these diverse data sets and allows us to assess all facets of the water quality management problem. Moreover, the explicit relationship of source, to sink, to export can tightly constrain predictions. It allows information on one aspect, such as export rates, to be used to constrain other aspects, such as the magnitude of the sediment supply. Information on the ratio of sediment or nutrient fluxes in different components of a budget provides further constraint. Hence, SedNet’s innovative approach offers several advantages over traditional sediment budgets as a modelling framework.
Authors
Dr Bruce Abernethy, Rebecca Lett & Henry Chaplin