Inputs into the NSW River Condition Index

The River Condition Index approach provides a consistent riverine condition assessment method. It includes riparian vegetation, geomorphic condition, hydrologic stress, biodiversity, catchment disturbance and water quality.

Riparian vegetation condition

A riparian zone or riparian area is the interface between land and a river or stream. Riparian vegetation are the plants occupying this zone. Riparian vegetation is more diverse and abundant than nearby terrestrial habitats. Healthy riparian zones provide many benefits, including:

  • habitat for native birds, reptiles, frogs, mammals and insects
  • shade to help moderate water temperature
  • organic input to waterways
  • bank stability
  • a filter for runoff that trap land-based sediment and nutrients.

The River Condition Index assesses riparian vegetation condition using:

  • riparian zone width
  • a measure of native versus exotic plant species
  • the extent of native woody vegetation.

Riparian vegetation condition

Geomorphic condition

Rivers are diverse in their physical character and behaviour. Human-induced changes in a catchment affect river processes.

Geomorphic condition measures natural channel function against its response to change. Rivers in good geomorphic condition are important for instream biodiversity, ecological diversity, and overall catchment condition. There is a strong connection between healthy floodplain, channel and groundwater. Rivers in poor geomorphic condition are indicative of stressed catchments. These rivers are unlikely to favour aquatic biodiversity. This is due to a reduction in geomorphic stability and available habitat. The connection between floodplain and groundwater is lost as the channel incises into its bed.

The River Condition Index uses the River Styles Framework to assess geomorphic condition. The River Styles approach scores river reaches according to their river type, behaviour, condition, fragility and recovery potential, relative to a reference condition.

River styles geomorphic condition

Hydrologic stress

Hydrologic stress is a measure of change to natural flow regimes in catchments. It is the amount of water extracted relative to river flow. Hydrologic stress shows the risks posed to instream values from extraction. It is an indicator of the degree of competition between extractors. Hydrologic stress helps to assess river condition.

Hydrolic stress A

Hydrolic stress B

River biodiversity condition

Aquatic biodiversity is the variety of plants and animals that live in aquatic habitats such as rivers and streams. Aquatic species include fish, macroinvertebrates, frogs, reptiles, aquatic and riparian vegetation. Aquatic species rely on healthy rivers and diverse habitats for survival and reproduction. These biotic indicators can help assess river condition. Reduced river condition is associated with loss of species.

River biodiversity condition

Catchment disturbance

Many activities in a catchment affect river health and resilience. These include land-use, habitat modification, infrastructure, and land management practices.

The Catchment Disturbance Index is a catchment summary of the type and extent of change in a catchment. It includes:

  • infrastructure
  • land-use
  • land cover change.

The infrastructure index measures the extent of roads, unsealed roads, railways, utilities (e.g. power, pipes) and walking tracks. The land-use index measures the extent of horticulture, orchards, cropping, cotton, rice, transport, production forests, grazing and wilderness/National park areas. The land cover change index measures the loss of woody vegetation using satellite imagery. The Catchment Disturbance Index helps to assess river condition.

Catchment disturbance

Water quality

Water quality is a key driver of aquatic ecosystem condition. Natural characteristics and human activities influence water quality and ecosystem condition. Local geology can influence salt and nutrient inputs to waterways. Climate, riparian vegetation and stream flow also influence water quality. There are a wide range of human activities that can impact water quality. These include water extraction, pollution and land use.

We are developing a water quality measure for inclusion in the River Condition Index. It will use data collected from routine monthly water quality sampling conducted throughout NSW. This is part of the NSW State Water Quality Assessment and Monitoring Program. Data includes turbidity, temperature, total nitrogen, total phosphorus, dissolved oxygen and pH measurements.