A water quality and quantity tool that models the amount of water and contaminants flowing into rivers, wetlands, lakes or estuaries is being used on the World Heritage listed Great Barrier Reef of Australia’s Queensland coast to reverse the decline in water quality on the reef.
The Source Catchments model (formerly known as WaterCAST and e2) is a spatially distributed water quality and quantity model developed by the eWater Cooperative Research Centre (CRC). It simulates the effect of climate and catchment properties (such as land use) on water quantity (runoff) and quality (contaminant loads) through unregulated catchments and into receiving water bodies
Catchment managers are required to forecast the quantity and quality of available water resources in catchments subject to many influences including bushfires, changing climatic conditions, diverse water management approaches and varied land use activities. This work is complicated by the interactions between these physical drivers on the catchments and by the expectations of the people that live and work in those catchments, such that they will continue to serve both their needs and the needs of the ecosystems. Catchment managers therefore need objective scientific evidence that the plans they are implementing will achieve great outcomes for their catchments and the communities that they support.
Source Catchments is comprised of a collection of models, data and knowledge for rainfall-runoff and water quality modelling. It has been widely applied to model loads of sediment, total nitrogen and total phosphorus and has also been used to model other contaminants such as salinity, coliforms, pathogens and pesticides.
Source Catchments models can support whole-of-catchment management and decision making.
The majority of existing models (such as SWAT, HSPF and Lucicat) rely on a single (or few) rainfall runoff and water quality models. An advantage of Source Catchments is that the user is able to select the appropriate rainfall-runoff model and water quality model from a wide range of component models, which provides the modeller with great flexibility to make the model reflect the physical response of the catchment.
Additionally, users are able to create and customise plug-in models if required.
A library of parameter values for constituent generation models is available to expedite model set up and benchmark performance. The parameter estimation model, PEST, has been applied with Source Catchments to efficiently calibrate the model to observed data and provide quantitative estimates of uncertainty.
Source Catchments also has an advantage over other models in that it is well documented, has a user friendly interface and provides parameter guidance for catchments established from applications. It can be less data intensive than some of the other commercially available water quantity and quality models.
Source Catchments allows users to:
- Determine the volume and quality of runoff entering creeks, rivers and water bodies due to rainfall (and groundwater if using the surface water-groundwater interaction module)
- Predict the volume of flow and contaminant loading at any point in a catchment
- Investigate the impacts of potential changes in climate, land use, bushfires or diversions on water quantity and quality throughout the catchment
- Assess the combined impact of multiple changes
- Identify key sources of catchment contaminants
- Determine locations for works to improve water quality.
As one of only two consultant partners to the eWater CRC, SKM has been Product Leader in the development of Source Catchments and also applied the model to a number of real-world project applications including:
- Nerang River freshwater health assessment study for Queensland’s Gold Coast City Council. A Model was developed of the mid and upper sections of the Nerang River catchment to assess current management actions and to develop future management actions for ecosystem and catchment health.
- Protecting Sydney’s water supply for the Sydney Catchment Management Authority, involving the development of a Model of the Nattai River Catchment flow and contaminant loads entering Lake Burragorang (Sydney’s main drinking water supply). The project considered a large range of contaminant sources including sewage discharges, septic tanks, urban areas, agriculture, farm dams and steep terrain to identify the location of diffuse contaminant sources and assess the relative important of point sources of contaminants across the catchment.
- Model to Predict Flows in the Googong Catchment for ActewAGL in the Australian Capital Territory, involving the development of a model to predict inflows to Googong Reservoir to allow separate accounting for the impact of changes in groundwater extractions, land use and farm dams impacts over time on the historic reduction in inflows.
Applications for Source Catchments
Source Catchments offers users a highly flexible, fully integrated modelling framework to simulate spatially distributed rainfall-runoff and water quality across catchments.
Source Catchments is part of the eWater Source suite of products and is interoperable with a range of river system, urban and ecological modelling tools. Software is available free until July 2011.
One of the reasons Source Catchments has been so successful is because it has evolved following extensive testing in a multitude of catchments to inform the process in each one, according to what happens in the catchment and what happens in the landscape. The model then accurately measures how water quality and quantity objectives are managed in each catchment.
Integration Needed
The model has been developed so that it works well at a catchment scale. It balances the need for mathematical sophistication against a requirement that a modeller is able to use the software without being overwhelmed by too much upfront complexity.
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Great Barrier Reef
In response to declining water quality in catchments near the Great Barrier Reef, which was threatening the long-term health of the reef, a Reef Water Quality Protection Plan was developed by the Australian Federal and Queensland Governments to improve the quality of water entering the reef by 2013.
The Queensland Government’s Department of Environment and Resource Management and eWater is working in catchments near the Reef, modelling land-use and the effects of changes in land management on runoff and water quality. Contaminated runoff is the single largest threat to water quality, introducing contaminants such as sediment, nutrients and agri-chemicals into the Great Barrier Reef lagoon.
For the waterways of the Reef’s catchments, the key values and priorities for the future are to:
- Halt and reverse the decline in water quality entering the reef within ten years (Reef Plan), and
- Rehabilitate and conserve areas so they can have a role in removing water-borne pollutants.
The challenges are being tackled by identifying hotspots in the catchments that are sources for sediment (TSS), nitrogen (TN) and phosphorus (TP), and developing management scenarios in consultation with local landholders and catchment groups.
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© Sinclair Knight Merz
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Who does this affect?
Water utilities, government agencies and all those involved in catchment management.
What do I need to do?
Understand the potential benefits of the Source Catchments eWater tool.
About the authors:
Dr Phillip Jordan is a senior hydrologist and SKM’s practice leader for catchment modelling.
Kate Austin is a senior water resources engineer and is SKM’s practice leader for water resource system modelling.
© Sinclair Knight Merz
Requests to re-publish achieve articles should be made here