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South West Index of river condition

assessing river health SerpentineThe 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.western pygmy perch

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 scoresSWIRC scoring circle example

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.

SWIRC scoring circle legendScores are divided into the condition bands represented in the table below.

SWIRC score  category

Condition  band

0.8 – 1.0

Largely unmodified

0.6 – 0.79

Slightly modified

0.4 – 0.59

Moderately modified

0.2 – 0.39

Substantially modified

0 – 0.19

Severely modified

No data available

 

The scores are represented in diagram below to provide acomprehensive view of river condition.

Further information

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 componentscollie river with fyke net

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 riverbed, 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 ofLive cobbler caught in a fyke net for river health assessment fish/crayfish and macro invertebrate 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 hot spots, encompassing some of the richest and most threatened reservoirs of plant and animal life.

Theme

Sub-theme

Component

Catchment disturbance

Land use

–

Land cover change

–

Infrastructure

–

Hydrological change

Flow stress ranking

Low flow

High flow

Proportion of zero flow

Monthly variation

Seasonal period

Farm dams1

Farm dam density

Farm dam development

Fringing zone

Extent of fringing zone

Fringing zone width

Fringing zone length

Nativeness

Ground cover layer

 

Shrub layer

Physical form

Artificial channel

–

Longitudinal connectivity

Major dams

Minor dams

Gauging stations

Road and rail crossings

Erosion

Extent of erosion

Bank stability

Water and sediment  quality

Total nitrogen

–

Total phosphorus

–

Turbidity

–

Diel dissolved oxygen

–

Diel temperature

–

Salinity

–

Non-nutrient contaminants

–

Aquatic biota

Macroinvertebrates

–

Fish and crayfish

Expectedness

Nativeness

Note:1These sub-themes donot currently have a scoring protocol in place hence they do not appear in thescore diagram above.

Page last updated - 24 Aug 2015
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The Department of Water and Environmental Regulation was established by the Government of Western Australia on 1 July 2017. It is a result of the amalgamation of the Department of Environment Regulation, Department of Water and the Office of the Environmental Protection Authority. This website/publication may contain references to previous government departments and programs. Please contact the Department of Water and Environmental Regulation to clarify any specific information.

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