Rivers - Assessment of River Condition
Australian River Assessment
Healthy rivers are important to Australians for the ecosystem services they provide (water supply and irrigation) and for the aquatic biodiversity that they support (such as water birds, fish, and aquatic plants). Rivers in good condition serve as benchmarks for assessing the condition of other rivers. Australian's also appreciate rivers for aesthetic, cultural, recreational and spiritual reasons.
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An assessment of Australia's Rivers
The assessment of river condition focuses on the aggregate impacts of resource use on Australia's rivers. Integrated assessments such as this one provide a basin-wide context and framework within which decisions and river management priorities can be considered.
The assessment incorporates a range of attributes that are considered to indicate key ecological processes at the river reach and basin levels. The two indices developed are an Aquatic Biota Index using macroinvertebrates, and an Environment Index with four sub-indices:
- catchment disturbance;
- hydrological disturbance;
- habitat; and
- nutrient and suspended sediment load.
The river basins assessed include areas that contain intensive land use and selected areas of non-intensive land use such as part of the Northern Territory and the western division of the Murray-Darling Basin. Whole river basins were used so that processes such as hydrology and sediment and nutrient movement could be modelled and balanced over entire catchments.
Generally, river basins are large areas with considerable diversity of river condition therefore a finer scale unit is required for assessing river condition.
River links are the stretches of river between tributary junctions and define a river network.
A river reach is an aggregation of river links that identifies a section of river with relatively uniform physical characteristics. A digital elevation model was used to calculate slope and drainage area. Together these give an estimate of stream power, which was used to define reaches as a continuous network from catchment to coast.
There were 14606 reaches identified in the assessment area (11028 of them are longer than 5km) and included in the assessment.
Description of Condition Classes
Reaches have been classified into 4 condition classes for each of the two indices:
Largely unmodified (Environment Index)
- minimal disturbance from catchment land uses such as conservation, some types of forestry, low levels of grazing or cropping;
- limited changes to the hydrological regime;
- limited changes to the physical habitat (e.g. riparian vegetation reasonably intact, no dams or levees and very little sediment deposition); and
- loads of suspended sediment, total nitrogen and total phosphorus close to natural.
Equivalent to reference site (Biota Index)
- Stream macroinvertebrates should be in similar numbers and of similar types to those at reference sites
Moderately modified (Environment Index)
- catchment dominated by land uses that disturb the river to some extent, such as dryland cropping and grazing;
- some changes to the hydrological regime as a result of impoundments or abstraction;
- some changes to physical habitat, e.g. riparian vegetation reduced to 50-75% original coverage, dams upstream but not in the reach, and some sediment deposition;
- loads of suspended sediment, total nitrogen and total phosphorus above natural.
Significantly impaired (Biota Index)
- Between 20 - 50% of the expected macroinvertebrates have been lost.
Substantially modified (Environment Index)
- catchment land uses with moderate to severe disturbance such as intensive cropping and irrigated land uses;
- substantial changes to the hydrological regime as a result of impoundments of abstractions;
- substantial changes to the physical habitat including loss of 50-75% riparian vegetation, connectivity affected by nearby dams or levees, and substantial sediment deposition; and
- moderate to high loads of suspended sediment, total nitrogen and total phosphorus.
Severely impaired (Biota Index)
- Between 50-80% of the expected macroinvertebrates have been lost.
Extensively modified (Environment Index)
- catchment land uses cause significant disturbance to streams such as intensive agriculture or urbanisation;
- significant changes to the hydrological regime, e.g. large reductions in flow and changes in the seasonality of flow events;
- extensive changes to the physical habitat including loss of riparian vegetation, loss of connectivity and extensive sediment deposition; and
- High loads of suspended sediment, total nitrogen and total phosphorus.
Extremely impaired (Biota Index)
- Between 80-100% of the expected animals have been lost
Results
Increases in nutrients and suspended sediment loads, and decreases in the extent of riparian vegetation have resulted in 85% of the river length being assessed as substantially or moderately modified from natural condition.
- Approximately 85% of the river length is affected by catchment disturbance. Land uses surrounding rivers affect delivery of sediment, nutrients and water to rivers. Reaches in Tasmania and the Northern Territory are the least affected by catchment disturbance.
- The natural flow baseline was available for only 25% of reaches in the assessment (or 30% of the total river length) making it difficult to measure the extent to which flow regulation and abstraction have affected rivers. Of the regulated and unregulated rivers that could be assessed, over 80% are modified to some extent and nearly 30% are substantially modified.
- Over half of the rivers assessed are affected by changes to riverine habitat with the worst affected areas occurring in the Murray-Darling Basin, South Australia and parts of the Western Australian Wheatbelt.
- Nutrient (mainly phosphorus) and suspended sediment loads are greater than natural levels for over 90% of the river length assessed and are severely modified in almost 10% of total river length.
Almost one third of the river length assessed is to some degree impaired (has lost between 20 and 100% of the various kinds of aquatic invertebrates that should live there).
New South Wales is assessed as having the poorest aquatic biota condition: approximately 50% of the river length assessed had impaired aquatic biota. Some of the most affected areas were the Georges River and Wollongong Coast basins.
Over 35% of the river length assessed in the Australian Capital Territory and Western Australia have impaired biota.
Between 12% and 24% of the river length assessed in the remaining States and Territories have impaired biota.
Australia-Wide Reporting of River Condition
A national protocol for reporting river condition has been developed for Atlas reporting and provides for the incorporation of results from river assessments at the State or regional level. This strengthens the overall results of the river assessment, as the best available information can be incorporated from the local, regional and State levels, without compromising the role of the national assessment.
The protocol:
- recognises that the Audit river assessment is an Australia-wide assessment and more detailed assessments at the State or regional levels already exist or will be developed over time;
- recognises that for comparable assessments to be considered they are required to be conceptually similar to the Audit river assessment;
- recognises that for comparable assessments to be considered they must be able to be linked spatially to the Audit river assessment;
- will adopt a precautionary approach whereby the result presenting the more conservative (least favourable) measure of river health or condition shall be applied;
- maintains the scientific principles and concepts underpinning the Audit river assessment; and
- will ensure that all decisions, results and assumptions are recorded and reported with the assessment results.
The reporting bands, ranges of results and nomenclature from comparable assessments will be evaluated and reviewed to produce a best fit with the Audit river assessment. Where the Audit river assessment or the comparable assessment does not report a value for a particular river reach then the assessment which has recorded a result will be utilised for that reach. Confidence limits will be determined for results from the comparable assessment, which fall within a range of the results from the Audit river assessment. For example in the case of the Index of Stream Condition, results falling within +/- 5% of each other will automatically be ascribed to the reporting range of the Index of Stream Condition. Where results differ by more than the ascribed confidence limits or by more than one reporting band, a case-by-case review will be undertaken against underlying data and other relevant information from the Audit river assessment and the comparable assessment, before subscribing the river reach to a condition ange. In all other cases the precautionary principle is applied, thereby assigning the more conservative (least favourable) condition assessment.
The reach results available from the on-line mapping facility have had the protocol applied to them.
Analysis of Patterns and Management Implications
Seven types of reaches with similar issues were identified by analysing the sub-indices which make up the Environment Index. Reaches with common problems do not necessarily occur in the same parts of the country, but some spatial patterns are evident.
River reaches that were classified 'largely unmodified' in all aspects (habitat, catchment disturbance and nutrient and suspended sediment loads) occur throughout the area of Australia assessed, especially in far north Queensland, eastern Victoria and Tasmania. These rivers require protective management to ensure their condition is maintained.
Rivers with the most urgent need for rehabilitation and strategic management are located in parts of the Murray-Darling Basin, the West Australian wheat-belt, western Victoria, and the South Australian wheat-growing areas. River reaches in these areas generally have highly modified catchments, are subject to high nutrient and suspended sediment loads, have lost much of their riparian vegetation and have dams and levees that disrupt the movement of biota and material into and from the river. (see Figure 1 below)
Figure 1: River reaches with highly modified catchments, which are subject to high nutrient and suspended sediment loads, have lost much of their riparian vegetation and have dams and levees that disrupt the movement of biota and material into and from the river.
The majority of river reaches in Queensland and reaches in northern coastal New South Wales, western Victoria and south-west Western Australia have largely unmodified habitat (bed condition, riparian vegetation, connectivity) but very high nutrient and suspended sediment loads. Erosion from hill slopes and stream banks is high, principally as a result of soil conditions and climate. Control of nutrient and suspended sediment loads is essential for rehabilitation of these streams. (see Figure 2 below)
Figure 2: River reaches with largely unmodified habitat(bed condition, riparian vegetation, connectivity) but very high nutriend and suspended sediment loads.
A small group of river reaches in central Tasmania, central Victoria, New South Wales and Northern Territory have severely modified habitat because of dams affecting longitudinal connectivity. However, catchment condition and nutrient and suspended sediment loads are 'largely unmodified' because vegetation cover is high. These reaches need protection and restoration of environmental flows and longitudinal connectivity (eg. fish ladders). (see Figure 3 below)
Figure 3: River reaches with 'severely moditied' habitat because of dams affecting longitudinal connectivity and 'largely unmodified' catchment condition and nutriend and suspended sediment loads because vegetation cover is high.
Summary of Methods
A detailed description of the methods is available in the project report, covering the following topics:
- defining the reach network;
- aggregation (i.e. aggregating measures for a group of reaches to provide a measure for a basin);
- integration (e.g. reach-scale sub-indices integrated to create the Environment Index for a reach);
- justification and descriptions of condition classes;
- calculations, modelling and validation of sub-index scores; and
- river sediment budget methods.
The assessment philosophy is based on departure from reference, or pre-European settlement conditions. Using the analogy of a financial audit, it is necessary to know how much is in the till relative to how much should be there. It is hard to find pristine rivers within the assessment area with which to compare test sites, especially for lowland rivers surrounded by extensive agricultural development. Therefore, reference conditions were set by a combination of minimally disturbed sites, historical data, modelling of past conditions, and professional judgement.
The reference condition used for each sub-index and details about the indices are in Table 1
River assessment indices and the reference conditions used for each.
Future Assessments
The results of the river assessment were limited by the data available. The assessment relied on disparate datasets provided by Commonwealth, State and Territory agencies. There are significant differences in the way data are recorded, stored and analysed across State borders. This made it difficult to collate and synthesise data into an Australia-wide assessment. Standardised site codes and location coordinate systems (including datum, projection and accuracy) would save much effort and reduce a major source of error.
For a future river assessment, the following improvements in Australia-wide datasets would increase the certainty and robustness of the assessment.
- Change to hydrology, a major driver of river condition, was insufficiently represented in the river assessment because of lack of baseline data. Although there are many stream-gauging stations collecting data in a standardised way across Australia, there are very few modelled hydrological data on flow regimes prior to European settlement. Future assessments also need updated data on extraction, catchment water yield and structures that modify hydrologic regimes.
- There is no Australia-wide dataset on riparian vegetation. Riparian vegetation is a critical ecosystem component, and information on its extent and condition is important for informed management.
- Data on other aspects of aquatic biota, such as fish, water birds and vegetation, are needed to augment the Australia-wide coverage of macroinvertebrate information.
- The National Pollutant Inventory should be expanded to include emission of biocides with arrangements put in place to require reporting of biocide use by agricultural enterprises, both intensive and extensive.
- Many of the water quality data collected across Australia are collected to provide information on specific issues, or to assess drinking or recreational water quality. If data were collected in a standardised way the accuracy of the assessment would be improved. Also, the inclusion of additional measures - water temperature, dissolved oxygen concentrations, and sediment and nutrient loads - would improve our understanding of water quality.
- Salinity is an increasing problem in many parts of Australia, for both land and rivers. Currently the database for stream salinity relies on sampling or continuous recording of salinity at a limited number of sites. This information could be augmented by development of a stream salinity model capable of predicting salinity concentrations based on catchment characteristics analogous to the sediment and nutrient models developed in the river assessment.
- There is a need to understand the impact of land management (e.g. land clearing) on rivers and in what time frame (ie. immediate vs. continuous impacts).
- Loss of habitat has been identified a major issue for most ecosystems, including aquatic ecosystems. Methods for assessing channel form and habitat, both in-stream and riparian, are needed.
- Pest species are known to have ecological impacts. Information is required about pest species extent and their interactions with riverine ecology.
Partnership
The river assessment was a partnership project between CRC Freshwater Ecology http://enterprise.canberra.edu.au/WWW/www-crcfe.nsf, CSIRO Land and Water http://www.clw.csiro.au/ and the Audit. Commonwealth, State and Territory agencies assisted by contributing data and reviewing the results.
Further Information
- Exit to more information on the AUSRIVAS home page for an introduction, models, taxonomy and downloads.
- the Assessment of River Condition:an audit of the ecological condition of Australian rivers (by R.Norris, I. Prosser, B. Young, P. Liston, N. Bauer, N. Davies, F. Dyer, S. Linke, and M. Thoms). (PDF 4418 KB)
- View the Audit's Australian Catchment, River and Estuary Assessment 2002
- View the Audit's Australian Agriculture Assessment 2001
- Link to Data Library to download data and metadata
- Link to the Map Maker to make a map using this information.
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