Index of Stream Condition (ISC)

Designed as a spatial benchmarking process the ISC is used to assess stream condition and detect long-term changes in overall stream condition over whole catchments.

The Index of Stream Condition (ISC) brings together data from a variety of sources to give a detailed overall picture of river condition. Five sub-indices make up the ISC score - Hydrology, Water Quality, Streamside Zone, Physical Form and Aquatic Life.  Each sub-index comprises individually measured variables.

The ISC is evaluated for individual river reaches, which are generally between 10 and 30km long, with similar hydrological, vegetation and landscape characteristics. Although, the 2013 documentation for the vegeation sub index was produced using LiDAR across the entire ISC network. Outputs from the ISC project feed directly into Catchment Management Authority (CMA) regional Waterway Health Strategies.

Sampling metrics for the ISC requires a combination of field and desktop approaches:

• Aquatic life indicators are collected via field sampling using AusRivAS, SIGNAL, EPT and assessing the number of macroinvertebrate families present
• The Hydrology metric is assessed using a combination of in-stream gauging and hydrological modelling
• Variables for Streamside Zone and Physical Form are measured using LiDAR and aerial photography, allowing for a wider site assessment
• Water Quality is measured using field sampling of physicochemical parameters

Each sub-index is rated against a reference condition and scored between 0 and 10 with the overall index scored out of 50. The overall score is not an aggregate of the five sub-indices. The ISC is weighted to recognise that a low score in one sub-index may have a limiting effect on stream health even if other sub-indices score highly. The total ISC score is categorised into one of five groups of condition - excellent, good, moderate, poor and very poor.

A benchmarking exercise of Victorian streams was carried out in 1999. The method was reviewed and variables changed or added where it could be shown the change was an improvement on the old method, it had been rigorously tested and it conformed to the original variable criteria. The revised methodology was used in 2004. Analysis of the results showed no major change had occurred since 1999. The third benchmark report in 2010 outlined further improvements from the 2004 methodology, most importantly, the addition of LiDAR and aerial photography for assessing Streamside Zone and Physical Form metrics. Additionally, the introduction of these techniques allowed for wider applications in flood risk mapping, flood warning, dam hydrology modelling and general management and planning.

Five key components of river health: hydrology, water quality, vegetation, physical form and aquatic life.

Long term stream flow data (15 years)

Field sampling:

• Water quality
• Aquatic biota and habitat

LiDAR and aerial photography for:

• Bank condition
• Artificial barriers
• Instream woody habitat
• Streamside vegetation condition, extent and distribution.

Ecologist, GIS, modellers, database management, water quality assessment

Access to stream flow data, five years of monthly water quality sampling data, Ecological Vegetation Class Benchmark (EVC), 'reference' water quality, field surveys.

• An integrated measure of stream condition using 5 sub-indices.

• To benchmark stream condition
• To inform reporting to local, regional, state or Commonwealth agencies
• To add objective setting by natural resource managers
• To provide feedback to natural resource managers
• To assess trade-offs between utilitarian demands on streams and environmental condition
• High level review of performance against expected outcomes.

Natural resource managers, regional NRM bodies, Waterwatch and community groups may find the ISC outputs useful.

• Uses information that is easily understood and collectible at the regional scale
• Methodologies are actively reviewed and improved
• Utilises a combination of desktop and field assessment.

• Requires a high level of skill, time and resources
• Specialised knowledge, equipment and tools
• to be used for monitoring requires detailed statistical designed and analysis capabilities

This page should be cited as:

Department of Environment, Science and Innovation, Queensland (2019) Index of Stream Condition (ISC), WetlandInfo website, accessed 18 March 2024. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/resources/tools/assessment-search-tool/index-of-stream-condition-isc/