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Phone: 1300 5 WATER (1300 5 92837)
Email: support@ewater.org.au

eWater
Innovation Centre
University of Canberra
ACT 2601
www.ewater.com.au

Features and Limitations

Input Data

SedNet requires data of four types including grids in Arc/INFO ASCII format:
  • Digital elevation model
  • Landuse
  • Hillslope erosion
  • Gully erosion
  • Riparian vegetation
  • Mean annual rainfall
  • Floodplain extent
ArcINFO Shapefile datasets:
  • Reservoirs
  • Lakes
  • Stream gauges
Comma Separated Value Time-series:
  • Daily timeseries of stream flow
Informational parameters:
  • Sediment density
  • Mannings-n channel roughness
  • Channel dimensions
  • Bedload particle size
  • Hillslope sediment delivery ratio
  • Soil nutrient concentrations
  • Dissolved nutrient runoff concentrations

Guidance on preparing high resolution datasets of particular catchments is contained in the SedNet User Guide.Many required datasets are publicly available with national Australian coverage.

File Formats

More information about supported file formats can be found in the Toolkit Data Files guide.


Output Data

SedNet predicts sediment supply in tonnes per year from surface or hillslope erosion, gully erosion, bank erosion. The ANNEX module predicts particulate nutrient (phosphorus and nitrogen) supply from each sediment source, organic and inorganic forms of dissolved nutrient supply from diffuse dissolved runoff, and also from point sources. The supplied material is routed through the river network, giving predictions of the rates of transport of bedload and suspended sediment, particulate and dissolved nutrients, floodplain and reservoir deposition and in-channel bedload deposition.

Results can be mapped, for example:

  • Mean-annual flow and other flow measures including bankfull flow
  • Predicted hillslope (surface wash) erosion
  • Gully erosion
  • Riverbank erosion
  • Suspended sediment transport
  • Bedload sediment transport
  • Bedload sediment accumulation
  • Predicted suspended sediment loads can be compared with measured loads, where long-term water quality observations are available.

Catchment summary budgets can help identify the proportion of sediment and nutrients supplied from each major source (hillslope, gully and riverbank erosion and dissolved diffuse and point source nutrients).


Caution Notes For User

SedNet is a regional-scale planning and priority setting technique. It may assist you to identify regional patterns in erosion rates, sediment and nutrient fluxes, and the causes of water quality problems. If you use only national-scale spatial datasets (e.g: from NLWRA), it is likely that the results will give only broad-brush indications of patterns in fluxes across a river basin. Higher resolution data is generally required to target management actions at the regional scale. Even with good quality input data, SedNet should not be used to design the location of individual management measures at site scale. Site inspections are always the best way to determine where and what to do to mitigate erosion and nutrient supply. Modelling sediment and nutrient budgets is a complex activity. Experience and knowledge of landscape processes are valuable aids in interpreting model operation and results. Users should check the reliability and accuracy of the results they have obtained before using them to make catchment management decisions, or to simulate the effect of proposed catchment changes. Keep in mind the limits of the model; the adage garbage in ? garbage out applies and poor quality input data produces poor quality results. You may find that existing datasets, for example the DEM, the hillslope or gully erosion maps, are inadequate and need to be replaced with datasets that better reflect the catchment condition. Evaluating the accuracy of datasets, or preparing new datasets, may be outside your area of expertise and you may need to seek specialist help. SedNet provides assessment of long-term averages in sediment and nutrient fluxes. Mean-annual results are valid for the period of input data used; greater than 20 years for suspended sediment and nutrients, and longer for bedload sediment. Disaggregating results can provide estimates of daily sediment loads and temporal patterns of delivery with uncertainty determined from the rating curves and observations available. Software testing completed: 1. Model algorithms: The results have been compared against those of the original ArcInfo implementation of SedNet in several catchments. Small differences can exist between Toolkit and ArcInfo results due to differences in the network generation algorithm, but these do not affect the utility of the results for the purposes listed in the User Guide. 2. Software use: The software has been run using datasets from several catchments. The "User Support" link to the email list archive contains experience of some users and some solutions for problems encountered with data formats etc. The "Bugs" link lists known bugs, including those fixed. The Release notes available from the "Download Software" link also describe known issues with software use. 3. Communication of Science: The tutorial has been worked through with users representative of the intended audience. There is always room for making tutorials more intuitive and users are encouraged to report difficulties they encounter while following the instructions.




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