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Phone: 1300 5 WATER (1300 5 92837)
Email:

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

Overview


Purpose

SedNet constructs sediment and nutrient (phosphorus and nitrogen) budgets for regional scale river networks (3,000 - 1,000,000 km2) to identify patterns in the material fluxes. This can assist effective targeting of catchment and river management actions at the regional scale, to improve water quality and riverine habitat.

A budget is an account of the major sources, stores and fluxes of material. SedNet defines a stream network as a series of links extending between stream junctions, and constructs sediment and nutrient budgets for each link. Spatial modelling is used to combine measurements of river discharge, a basic understanding of material transport processes and geographical mapping of soils, vegetation cover, geology, terrain and climate. Details of the technical basis of SedNet are described in the SedNet User Guide.


Target user group

SedNet is suitable for use by:

  • Catchment and regional planners, waterway managers, project managers, strategy developers, GIS / data managers.
  • Environmental consultants.
  • National, State and Regional natural resource management agencies.
  • Water and catchment management authorities.
  • Local government authorities with an interest in rural water quality management.

Complexity

SedNet has been designed for a range of different users with different backgrounds, however modelling sediment and nutrient budgets is a complex activity. GIS and data analysis experience is required for initial construction of a catchment SedNet model. Experience and knowledge of landscape processes are valuable aids in interpreting model operation and results.


Example applications

Targeting erosion control and other management measures to dominant sources can achieve a large benefit in reduced sediment and nutrient loads downstream with comparatively less resources than for non-targeted management. With careful data preparation, SedNet can assist planning of catchment management actions by identifying the relative importance of processes supplying sediment and nutrients to the river network, and hotspot areas of each source.

SedNet accounts for deposition of sediment in the stream network. If the management objective is to reduce catchment export to limit downstream impacts, accounting for deposition is important because not all areas of erosion result in export of sediment from the catchment. Suspended sediment deposits in reservoirs and floodplains. Bedload sand and gravel can accumulate on the bed of rivers and degrade aquatic habitat, particularly along low-gradient reaches of streams when the upstream sediment supply is in excess of the reach's capacity to transport it.

The effect of proposed changes in catchment management on sediment and nutrient fluxes can also be simulated to set targets for future loads and to compare the relative effectiveness of different management strategies on long-term supply and yields from river networks. Features are provided for simulating changes to:

  1. Riparian vegetation; affecting bank erosion
  2. Gully Stabilisation; affecting gully erosion
  3. Landuse and hillslope vegetation cover; affecting hillslope erosion
  4. Flow regulation and diversions; affecting bedload sediment transport capacity, bank erosion and floodplain deposition.
  5. Dissolved nutrient runoff concentration; affecting dissolved nutrient supply.

Overview of features, advantage and benefits

Differentiating features of SedNet relative to other models of regional water quality include:

  • SedNet explicitly represents supply processes (hillslope, gully riverbank erosion, diffuse and point nutrient supply) to assist targeting of specific management measures.
  • Represents floodplain and reservoir deposition, important for assessing delivery to the catchment outlet.
  • The effects of temporal variability in climate and stream flow etc. are integrated to predict material budgets that represent average conditions for periods of twenty plus years, rather than estimates over short time-steps. This temporal integration clarifies the spatial patterns, and is appropriate for most planning activities since management actions such as riparian revegetation take decades to reach their full effect and it is their long-term impact that is of interest. Results can be disaggregated to predict daily loads using rating curves and flow time-series if required.
  • Budgets can be compared with "natural" conditions.
  • Models both suspended and bedload sediment movement.
  • The ANNEX (Annual Network Nutrient EXport) module speciates dissolved nutrients into organic and inorganic forms.
  • SedNet has been applied and tested in many Australian river basins.

Material budgets are constructed in SedNet using Configurations and Scenarios. A Configuration contains the stream network and several catchment attributes that do not change. It is the framework on which the budgets are constructed. Each Configuration can contain several Scenarios, each containing the datasets, parameters and results associated with a particular catchment condition, whether historical, present-day or a simulation of possible future condition.

The layout of the SedNet interface can be customised by arranging dockable windows to suit user requirements. The interface contains a Map Frame for viewing maps of input and output data.





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