South West Index of river condition
The Department of Water assesses the condition of rivers and estuaries in order to manage these valuable water resources. We use a range of indicators to assess condition – the South West Index of River Condition (SWIRC) brings a large number of these indicators together into a single tool for assessing river condition in south-west Western Australia.
The SWIRC provides:
- a suite of standardised methods for collecting field and desktop data
- a suite of protocols for analysing field and desktop data, including a standardised system for scoring river condition.
The SWIRC includes six key ecological themes representing ecological integrity: aquatic biota, water quality, fringing zone, physical form, hydrological change and catchment disturbance. Each theme is divided into a series of sub-themes and components (see Summary box below). The SWIRC is continually developing and may include additional sub-themes and components in the future.
The SWIRC tool is very flexible – we can tailor our river condition assessment to suit individual circumstances. We can use all the indicators in the suite to generate a comprehensive assessment of all aspects of river condition, or we can choose to focus our assessment on a sub-set of indices to answer specific questions about managing a water resource (for example, when assessing summer refuge pools we focus on water quality and aquatic biota to see how they respond to reduced flows during hot weather).
South West Index of River Condition scores
The SWIRC includes a standardised system for scoring each of the indicators. This allows the results to be compared between river systems across south-west Western Australia. The scoring system complies with the national Framework for the Assessment of River and Wetland Health (FARWH), and can be used to generate data for national comparison and reporting purposes.
The scoring protocols are based on a reference condition approach. Each score provides a measure of the departure of the observed values from expected values. The expected values are those typically anticipated under minimal disturbance conditions, and can be derived from historical data, data from minimally disturbed sites or expert opinion.
Scores are divided into the condition bands represented in the table below.
SWIRC score category
0.8 – 1.0
0.6 – 0.79
0.4 – 0.59
0.2 – 0.39
0 – 0.19
No data available
The scores are represented in diagram below to provide a comprehensive view of river condition.
Details about the development of the SWIRC and the standardised methods for data collection analysis (including scoring) can be found in the following reports: The Framework for the Assessment of River and Wetland Health (FARWH) for flowing rivers of south-west Western Australia: project summary and results and method development. Please contact the Water Science Branch of Department of Water for further information.
The following river health assessments were conducted using the standard SWIRC methods:
- Ecological study of the lower Canning River environmental water releases (below Canning Dam to Kent Street Weir)
- Ecosystem health in the Canning River, focusing on the influence of the Kent St Weir : assessed December 2009 - September 2011
- Assessment of low-flow thresholds in maintaining ecological health of the Gingin Brook : 2010-2011 dry season
- Assessment of low-flow thresholds in maintaining ecological health of the Lennard Brook : 2010-2011 dry season
- Assessment of ecological health and environmental water provisions in the Harvey River (between Stirling Dam and Harvey Reservoir) : February to May 2011
- Assessment of ecological health and environmental water provisions in the Logue Brook : February to May 2011
- River health assessment in the lower catchment of the Blackwood River
SWIRC themes, sub-themes and components
The catchment disturbance theme measures the land use and vegetation clearing occurring in a catchment. These disturbances can impact river health via changes to flow, increased erosion and sedimentation, increased nutrients and non-nutrient contaminants, and increased salinisation. Given the broad range of these impacts, the catchment disturbance theme is a key indicator of pressure on a waterway. It provides valuable information about the causes of river health issues and highlights potential future impacts.
The hydrological change theme characterises the flow regime using the flow-stress ranking (this considers low and high flow, zero flow, monthly and seasonal variability) and the extent of farm dams in the catchment. It reflects the importance of the flow regime to the health of a river via water connectivity, erosion and the transport of nutrients and sediment. The hydrological change theme helps us to differentiate between ecological impacts due to altered flow and impacts due to other pressures.
The fringing zone theme assesses the extent of vegetation along a river channel and the condition of the vegetation present. Fringing or riparian vegetation is important for the health of waterways, contributing to the balance of oxygen, nutrients and sediment, and providing shade, habitat and food for fauna. The fringing zone indicators provide a measure of the status of the fringing vegetation, which is recognised as an ecological value, and helps us to understand pressures influencing the aquatic biota community.
The physical form theme assesses the availability of habitat at three spatial scales: micro-scale habitat of the river bed, macro-scale habitat such as pools and riffles, and system scale connectivity. Physical form indicators provide a measure of the pressure being placed on aquatic biota via alterations to habitat.
The water and sediment quality theme measures the status of various parameters including nutrients, turbidity, oxygen, temperature, salinity and non-nutrient contaminants. Water and sediment quality are important indicators as they reflect land use activities in the catchment and provide information about pressures influencing the aquatic biota community.
The aquatic biota theme assesses the condition of fish/crayfish and macroinvertebrate populations. Aquatic biota are an important indicator of river health as they reflect impacts to an ecosystem from a range of pressures, providing a direct measure of the condition of a water resource. Biological indicators can also detect problems that may be missed or underestimated by other methods and indicators.
Aquatic biota are also recognised as an ecological value for protection, particularly in the south-west of Western Australia which has been identified as one of the world's biodiversity hotspots, encompassing some of the richest and most threatened reservoirs of plant and animal life.
Land cover change
Flow stress ranking
Proportion of zero flow
Farm dam density
Farm dam development
Extent of fringing zone
Fringing zone width
Fringing zone length
Ground cover layer
Road and rail crossings
Extent of erosion
Water and sediment quality
Diel dissolved oxygen
Fish and crayfish
Note: 1 These sub-themes do not currently have a scoring protocol in place hence they do not appear in the score diagram above.