NSW River Condition Index

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
• the extent of native woody vegetation
• the extent of native non-woody vegetation
• landscape connectivity (fragmentation and patch size).

Figure 1. Good versus poor riparian vegetation 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.

Figure 2. Good versus poor geomorphic condition

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.

Figure 3. Hydrologic stress in low flow conditions and water extraction in low flow conditions.

Figure 4. Hydrologic stress in no flow conditions and water extraction in no flow conditions.

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.

Figure 5. Good versus poor river biodiversity condition.

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 helps to assess river condition and includes the following features:

• infrastructure
• land-use
• land cover change.

Infrastructure measures the extent of roads, unsealed roads, railways, utilities (e.g. power, pipes) and walking tracks. Land-use measures the extent of horticulture, orchards, cropping, cotton, rice, transport, production forests, grazing and wilderness/National park areas. Land cover change measures the loss of woody vegetation using satellite imagery.

Figure 6. Good versus poor catchment disturbance.

Water quality is a key driver of aquatic ecosystem condition. Both natural characteristics and human activities can influence water quality and thus ecosystem condition. For example, local geology can influence salt and nutrient inputs while climate, riparian vegetation extent and health, and stream flow influence sediment and nutrient loads. There are a wide range of human activities that can impact water quality. These include water extraction, pollution and changed land use.

Figure 7: Good versus poor water quality.