australia’s rivers - evolving water managementfile/ch14spa.pdf · volumes of water for...

Australia’s riversThis article was contributed by John Whittington and Peter Liston of

the Cooperative Research Centre for Freshwater Ecology.

By world standards Australia is a dry continentwith few freshwater resources. Australian riversare characterised by relatively low and variableflows.

In much of the intensive land use zone ofAustralia, catchment land use has significantlymodified the physical and chemical nature of therivers. These now carry higher than natural levelsof sediment and nutrient. In some regions, thebiological condition of the rivers, wetlands andgroundwater dependent ecosystems has beenseverely impacted by the extraction of largevolumes of water for agricultural, urban andindustrial use.

It is widely recognised that the condition of manyof Australia’s rivers has declined below a level thatthe broader community considers satisfactory.The states, with Federal Government support, areacting to improve catchment management andreduce the ecological pressures associated withhigh levels of abstraction.

Variability — a characteristic ofAustralia’s riversRainfall is distributed unevenly, bothgeographically and seasonally, across Australia. Invast areas the average annual rainfall is less than200 mm/year, while in parts of north easternQueensland and western Tasmania rainfallexceeds 3,000 mm/year. Most of this rainfall, evenin the wetter catchments, does not run off intothe river systems. On average, only 12% (less than3% in the drier areas and up to 24% in the wetterareas) of rainfall enters the rivers; the remainingrainfall is accounted for by evaporation, used byvegetation or stored in lakes, wetlands andgroundwater aquifers. Almost 50% of Australia’saverage annual run-off enters the Gulf ofCarpentaria, a region of relatively limited waterresource development, and the Timor Sea(NLWRA 2001b).

Driven by a changeable climate, variable riverflow is a characteristic of Australian rivers.Flow variability can be described by thecoefficient of variation of annual flows (CVR),calculated as the standard deviation divided bythe mean. Australia and South Africa have CVRwell in excess of the world average (Finlayson& McMahon 1988). While this relationship istrue for all catchment sizes, it is particularly sofor Australia’s large (greater than 100,000 km2)inland catchments, which have a CVR of 1.12,nearly four times the world average of 0.33. Aswell as more variable flow, extreme floodsoccur more often in Australia and South Africathan in the rest of the world (Finlayson &McMahon 1988).

Highly variable flows have importantimplications for river management as theflora and fauna of Australia’s rivers haveevolved with this variability. River regulationby dams reduces the numbers and extent offloods and dry periods, and reduces waterquality. These changes affect the way theriver functions physically and chemically, inturn impacting on the plants and animalsliving there.

The high run-off variability and extreme floodpattern influence the size and type ofAustralia’s major dams. The level of demandand reliability expected by Australian waterusers, combined with the high levels ofevaporation in Australia, has led to Australia’srelatively high storage volumes. Australia’slarge dam storage capacity of 79,000 GL (in447 large dams) is four times annual surfacewater diversions of 19,100 GL (NLWRA 2001b).

Pressures on the riversThe consumption of Australia’s freshwaterresources from lakes, rivers andunderground aquifers has increaseddramatically in the last two decades. Between1983–84 and 1996–97 national waterconsumption increased from 14,600 GL to

23,300 GL (NLWRA 2001b). Of the water divertedin 1996–97, approximately 75% was used forirrigated agriculture (17,356 GL), 5% (1,238 GL)for other rural purposes such as stock anddomestic uses, with the remaining 20%(4,673 GL) for urban and industrial purposes(NLWRA 2001b).

Irrigated agriculture is by far the biggestconsumer of Australia’s freshwater resources. Inreturn, major economic and social benefits accrueto Australia from irrigated agriculture. Withoutirrigation, a significant proportion of Australia’sagricultural industries would either not exist orwould be greatly diminished. Towns andindustries that rely on these enterprises wouldcontract or disappear. Total annual profits fromirrigated agriculture averaged over the five yearsto 1996–97 were $3.84b, accounting for over 50%of the total profits from Australian agriculture(NLWRA 2002b).

Across Australia, catchment land use anddiverting water are considered the most seriousthreats to the ecological condition of Australia’srivers, wetlands and groundwater dependentecosystems. Determining a sustainable level ofdiversions (sustainable yield) to support eitherrural, urban or industrial use is complex. Itinevitably requires a trade-off betweenenvironmental, cultural, social and economicvalues. Each state and territory government hasdeveloped its own methods for estimatingsustainable yield. The relative weighting given tovarious social, environmental and economicvalues reflects local knowledge and values. Aswould be expected, the weightings given to thesevalues are often highly contentious.

Based on state assessments of sustainable yieldthe Audit (NLWRA 2001b) determined that 34(10.5%) of Australia’s 325 surface water basins areoverused, with a further 50 (15.4%) highlydeveloped. On the other hand, 60% of Australia’sriver basins have less than 30% of the nominatedsustainable flow regime diverted (NLWRA 2001b).Almost all of the basins with a high volume ofunused sustainable yield are in the northern partsof Australia. Undoubtedly, these regions will beheavily targeted for water resource developmentin the future, and long-term planning for thisneeds to be undertaken so as to avoid themistakes made in many of the southern waterbasins.

Land use in the catchment, combined withhow well this use is managed, is a majordriver of river condition. Approximately 60%of the Australian continent is used foragriculture, predominantly cropping andgrazing (NLWRA 2002b). In the non-urbanregions, most of the elevated nutrient andsediment loads to rivers are a consequenceof using land for agricultural production.High fertiliser application rates, and otheragricultural practices, have resulted in somelandscapes leaking more nutrients into thewaterways than they did before the adoptionof European agricultural production systems.Attention to management of on-farmnutrient balances should reduce the leakageof nutrients into Australian rivers(NLWRA 2001a).

Widespread clearing, particularly of theriparian vegetation and in areas vulnerable tosoil erosion, results in higher than naturalsediment loads to many rivers. Increasedsediment loads smother important habitatfor aquatic biota, for example, deep holes inrivers that provide important refuges formany native fish and other biota arefrequently filled in. Increased sediment loadsalso increase turbidity, resulting in reducedaquatic plant growth and increased costs ofwater treatment. The Audit estimates that a5% increase in turbidity of Australian streamswill increase water treatment costs by $715mover the next 20 years (NLWRA 2002b).

River condition depends oncatchment conditionUse of Australia’s land and water resourcesplaces pressures on the river systems. TheAudit describes the impact of these pressureson the condition of Australia’s rivers(NLWRA 2002a).

The Audit reports catchment conditionacross Australia using an index composed of14 sub-indices that describe attributes of thecatchments, land, water and biota. Thedifferences in the condition betweencatchments were described by a fewindicators: vegetation cover, nativevegetation fragmentation, sediment andnutrient inputs to rivers, catchmenthydrology (particularly the effects of dams),and land use intensity (NLWRA 2002a). Thecatchments in the poorest condition were inareas with intensive land use. These

450 Year Book Australia 2003

catchments are generally in cleared,agronomically marginal rainfall areas that havesoils of relatively poor fertility and structure(map S14.1) (NLWRA 2002a). Until the conditionof these catchments is significantly improved, weshould expect that river condition in thesecatchments will continue to decline.

The Audit (NLWRA 2002a) describes rivercondition using an environmental index thatcombines the effects of catchment disturbance,

habitat condition, hydrological disturbance,and nutrient and suspended sediment loads.The environmental index shows that withinthe intensive land use zone of Australia,which represents approximately 40%(3 million square kilometres) of thecontinent, over 85% of the rivers have beendegraded to some extent by human activity(map S14.2). The percentage of riversignificantly modified, ranges from 97% ofriver length in New South Wales rivers to34% in Northern Territory (NLWRA 2002a).

S14.1 CATCHMENT CONDITION FOR 5 KM x 5 KM CELLS

Source: National Land and Water Resources Audit Assessment of Catchment Condition 2002 Database.

Chapter 14 — Environment 451

Better

Moderate

Poorer

Not assessedBasin and state boundaries

S14.2 CONDITION OF RIVER REACHES BASED ON THE ENVIRONMENT INDEX


The Audit reports a relatively high correlationbetween catchment condition and river conditionas described by the Environment Index (NLWRA2002a). While these indices are not entirelyindependent, the strong correlation underscoresthe need to consider broad catchmentmanagement as part of any river managementprogram.

The rivers are carrying morenutrient and sedimentAustralia’s history of agricultural practices hasresulted in an accelerated leakage of nutrientand sediment from Australian landscapes.The Audit (NLWRA 2002a) reports thatnutrient and suspended sediment loads to besignificantly higher than natural levels for92% of river length (map S14.3). Totalphosphorus (TP) loads in rivers averaged2.8 times higher than estimates forpre-European settlement levels and total


Largely unmodifiedModerately modifiedSubstantially modifiedSeverely modifiedNot assessed

Reach condition

nitrogen (TN) loads are 2.1 times higher (NLWRA2001a). Exceeding national guidelines for nutrientconcentrations is a major concern in 61% of riverbasins (NLWRA 2001b).

The dominant sources of TP and TN to the riversvary depending on the local climate, geography,geology and land use. In Queensland and NewSouth Wales, hill-slope erosion dominates, whilein coastal Victoria, South Australia, WesternAustralia and Tasmania, river bank erosion anddissolved phosphorus run-off dominates.TN loads come predominantly from hill-slopeerosion in Queensland and coastal New SouthWales, and as dissolved run-off in coastal Victoria,South Australia, Tasmania and much of WesternAustralia (NLWRA 2001a). Most nutrient andsediment entering the waterways are depositedon floodplains. Of the TP entering the waterways,60% is deposited on floodplains, 13% inreservoirs and 27% reaches the coast. Of the totalTN entering the river systems, 41% is depositedon floodplains, 9% stored in reservoirs, and 39%reaches the coast. The remaining 11% isconverted to nitrogen gas and lost to theatmosphere.

Accumulation of sand and gravels is a majorstressor in many Australian streams. Extensivedelivery of sediment to the rivers occursdownstream from areas of hill-slope erosion(50 million tonnes per year), gully erosion(44 million tonnes per year) and streambankerosion (33 million tonnes per year) (NLWRA2001a). Most of the sediment supplied to rivers isdeposited in channels, floodplains and reservoirs,with about 20% entering the ocean(NLWRA 2001a).

About 30,000 km of river length have experiencedsediment accumulation of greater than 0.3 metressince European settlement. The Murray–DarlingBasin is one of the worst affected basins, with20% of river length accumulating more than0.3 metres of sediment. Land management thattargets erosion control could provide a significantbenefit to managing supply sediment loads andnutrient loads to many rivers.

The rivers have less waterAssessing the impact of human activities on theflow regime of Australia’s rivers is complicated bythe relative lack of suitable hydrologicalinformation. The Audit found adequate

information on which to determine naturalflows for only 30% of the total river length inAustralia’s intensive land use zone (NLWRA2002a).

Rivers below major dams, termed regulatedrivers, generally flow for longer periods thannatural, and the seasonal variability in flows isreduced (NLWRA 2002a). There are fewersmall floods and dry periods and there isfrequently a reversal of seasonal flows, suchthat water is retained in the dams during thewetter periods and rivers run high during thedry periods to supply irrigation water.

Less is known about the level of hydrologicaldisturbance in rivers which do not havemajor dams above them. Flow is frequentlyreduced by abstraction, particularly duringthe low flow periods, but estimates of thisare generally crude and are usually made onan annual or seasonal basis (NLWRA 2002a).Large-scale harvesting of floodwaters occursin some river systems, where privatefloodplain storages can capture a significantproportion of flow. For example, there issignificant floodplain harvesting on theBalonne floodplain. Total water storage onthe Balonne floodplain is estimated to be1,160 GL, which is equivalent to the currentmean annual flow in the Balonne River(Whittington et al. 2002).

Aquatic animals reflect river andcatchment useAcross the world there has been a trendtoward using assessments of the condition ofbiotic communities to assess river condition.It is argued that the plants and animalsdependent on a river will integrate the effectsof environmental degradation and ofpollution and are therefore the fundamentalindicators of river condition (Norris & Thoms1999). While there are many biologicalindicators that could be used, there are verylimited data for most of them. The mostcomprehensive data set for aquatic biota isthe information from the National RiverHealth Program (NRHP). This programassessed river health using aquaticmacroinvertebrate communities atapproximately 6,000 sites across Australia,and provides the most comprehensiveassessment of biotic river health availableacross Australia.


S14.3 CONDITION OF RIVER REACHES BASED ON THE NUTRIENT AND SUSPENDED SEDIMENTLOAD INDEX


Based on data from the NRHP, the majority ofrivers (69%) across Australia were found to be ingood condition (NLWRA 2002a). The remaining31% were suffering for some degree ofimpairment, ranging from mild impairmentwhere some of the animals normally occurring ina river were missing, to major damage wheremost animals were missing. The rivers with biotain good condition tended to be in national parks,mountainous regions or remote regions. Riversshowing impact tended to be close to major cities

or in highly developed agricultural areas.Also impacted were rivers in mountainousregions affected by river regulation.

The environmental factors most significantlyimpacting on river biological condition werepoor water quality, damaged habitat,changed hydrological condition or acombination of these factors. Regions such asthe Murray–Darling Basin, with considerableriver regulation associated with intensiveagricultural development, tended to have


Largely unmodifiedModerately modifiedSubstantially modifiedSeverely modifiedNot assessed

Reach condition

poor biological condition brought on byenvironmental degradation across multiplefactors (NLWRA 2002a).

Biological data do not always give the samepicture on river condition as do environmentaldata. In part this is attributable to the limits ofone group of the biota to reflect the full range ofenvironmental changes that can occur. Fish oralgae may be better indicators for someenvironmental impacts. However, in manyinstances, a more important reason for themismatch between biological and environmentalassessments is the timelag betweenenvironmental damage occurring and itsbiological consequences. It may be months oryears before the full impact of a change in riverflows or in salinity is realised by the biota. Inthese circumstances the degraded environmentalcondition can act as an early warning of thebiological damage that will occur unlessrestoration measures are undertaken.

Protection of freshwater ecosystemsAustralia has a poor record of managing aquatichabitats. Responsibility for land and watermanagement lies with the states and territories,though the Federal Government has been asubstantial source of funding for water resourcedevelopment and more recently, rehabilitation.Within most states there has been considerableactivity to provide adequate flows for theenvironment. This has been largely driven by theWater Reform Agenda of the Council of AustralianGovernments, which states that the environmentbe recognised as a legitimate user of water, andthat each jurisdiction formally determineallocations for the environment. However,despite considerable activity, progress has beenslow. As at June 2000, only 43 (13%) of Australia’s325 river basins have formal allocations of flow tothe environment (NLWRA 2001b).

Conservation of Australia’s ecosystems hashistorically focused on protection of terrestrialecosystems. Within the 7.8% of Australia’s totalland area that is within formally protected areas,some native terrestrial ecosystems are wellprotected and others are not (NLWRA 2001c).Recent efforts to increase the comprehensivenessof protected ecosystems have prioritisedbioregions that have relatively low levels ofprotection using the Interim BiogeographicRegionalisation for Australia (IBRA) framework.While the IBRA bioregions are an acceptedlandscape framework for conserving terrestrial

biodiversity (Cresswell & Thomas 1997), theyare unlikely to be an appropriate frameworkfor conserving aquatic biodiversity. If aquaticecosystems fall within existing reservesystems, such as parts of the Australian Alpsand south-west Tasmania, they can beadequately protected. However, this is notusually the case, and therefore frameworksthat explicitly address the diversity of aquaticecosystems need to be developed. Such aframework has been proposed by Davies(2001), which provides for the establishmentof a freshwater and estuarine reserve systembased on the principles ofcomprehensiveness, adequacy andrepresentativeness, (CAR reserve system) in asimilar way to that described for forestreserves (JANIS 1997). This is currently beingimplemented in Tasmania.

Like rivers, wetlands are not adequatelyprotected. It is estimated that sinceEuropean settlement approximately 50% ofAustralia’s wetlands have been converted toother uses. In some regions the rate of losshas been even higher (Commonwealth ofAustralia 1997). Of those remaining, manyare threatened by water abstraction, weedsand grazing. The Federal Government has apublished a Directory of Important Wetlandsin Australia (Environment Australia 2001).The directory describes 851 wetlands(totalling 57,829,522 ha) of nationalimportance, but protection of these is highlyvariable. Of these wetlands, 57 wetlands, witha total surface area of 5,310,179 ha, aredesignated to the List of Wetlands ofInternational Importance of the RamsarConvention, referred to as Ramsar wetlands.Once listed as a Ramsar wetland, the FederalGovernment must ensure that the wetland ismanaged such that its ecological character ismaintained. However, the protected status ofmany of Australia’s Ramsar wetlands iscompromised because protection does notextend to the source of the wetland’s water.For example, as a result of water abstractionupstream, median annual flows to theRamsar listed Narran Lakes in northern NewSouth Wales have been reduced toapproximately 24% of natural, and theinterval between significant flooding eventshas been reduced from 2 years to 6.5 years(Whittington et al. 2002). It is argued thatwithout significant alterations to watermanagement upstream of Narran Lakes, the


current level of diversion will result in asignificant reduction in the health of the NarranLakes system (Whittington et al. 2002).

There is growing recognition of the value of thefew relatively unimpacted rivers in Australia(Cullen 2002). However, efforts to protect these

aquatic systems are limited (Cullen 2002).Morton et al. (2002) have called for theestablishment of a system of heritage riversto protect the remaining relativelyundamaged rivers. Cullen (2002) argues thatthe extraction of water is the majorthreatening process in these rivers and mustbe controlled.

ReferencesCommonwealth of Australia 1997, The Wetlands Policy of the Commonwealth Government of

Australia.

Crabb P 1997, Murray–Darling Basin Resources, Murray–Darling Basin Commission, Canberra.

Cresswell ID & Thomas GM (eds) 1997, Terrestrial and Marine Protected Areas in Australia, EABiodiversity Group, Canberra.

Cullen P 2002, The Heritage River Proposal — conserving Australia’s undamaged rivers, WorldCongress on Aquatic Areas, Cairns.

Davies P 2001, Strategic Environmental Issues Scoping Report, Water Development Plan ForTasmania, Department Primary Industries, Water and Environment, Tasmania.

Environment Australia 2001, A Directory of Important Wetlands in Australia, Third Edition,Environment Australia, Canberra.

Finlayson BL & McMahon TA 1988, ‘Australia Vs the World: a comparative analysis of streamflowcharacteristics’, in Robin F Werner (ed.), Fluvial Geomorphology of Australia, Academic Press,Sydney.

JANIS 1997, Nationally Agreed Criteria for the Establishment of a Comprehensive, Adequate andRepresentative Reserve System for Forests in Australia, a Report by the Joint ANZECC/MCFFANational Forest Policy Statement Implementation Sub-committee, ANZECC, Canberra.

Morton S, Bourne G, Cristofani P, Cullen P, Possingham H & Young M 2002, Sustaining our NaturalResources and Biodiversity, an independent report to the Prime Minister’s Science, Engineeringand Innovation Council, CSIRO and Environment Australia, Canberra.

NLWRA (National Land and Water Resources Audit) 2001a, Australian Agricultural Assessment,National Land and Water Resources Audit, Canberra.

NLWRA 2001b, Australian Water Resources Assessment 2000, Surface water and groundwater —availability and quality, National Land and Water Resources Audit, Canberra.

NLWRA 2001c, Australian Native Vegetation Assessment, National Land and Water Resources Audit,Canberra.

NLWRA 2002a, Australian Catchment, River and Estuary Assessment Vol 1, National Land and WaterResources Audit, Canberra.

NLWRA 2002b, Australians and Natural Resource Management, National Land and Water ResourcesAudit, Canberra.

Norris RH & Thoms MC 1999, ‘What is river health?’, Freshwater Biology, 41, pp. 197–209.

Whittington J, Bunn S, Cullen P, Jones G, Thoms M, Quinn G, & Walker K 2002, Ecologicalassessment of flow management scenarios for the Lower Balonne, CRC for Freshwater EcologyTechnical Report, Canberra.


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