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Every time another wildfire rages througha forest in Australia, an opportunity arisesto learn more about the interplay betweenfire, forests and catchment management.The unprecedented firestorm that torethrough eucalypt forest, woodland, grass-land and pine plantations, and into severalCanberra suburbs in January 2003 has re-ignited debate on the best way to deal withfire in water-supply catchments. How doessevere fire affect water-supply catchments?What happens to water yield and quality?Is commercial forestry a good idea in watercatchments?

Impacts of the 2003 wildfiresFires raged throughout the eastern states ofAustralia during the hot and dry summerof 2003. In all, blazes affected about 1.5million hectares of south-eastern Australia.Nowhere was the devastation greater thanin the ACT, where on January 8 severalfires were caused by lightning strikes in theBrindabella Ranges, to the west of the ACT.At first the fires burnt slowly and remainedsmall. However, on January 18, fanned bywinds of up to 100 km per hour, and withhot dry weather, the fires spread withfrightening speed and in one day burnt anarea of 1649 square km.

Some 70% of the ACT was affected byfire, four lives and 500 homes were lost and50 000 electricity customers and 7000 gascustomers went without services. Watersupply was lost for some hours and sewagetreatment was disrupted for two days.

The horrendous fire, which came aftersix years of below-average rainfall andmonths of severe drought, blotted out the

sun and caused several tornadoes. It burntright across Canberra’s main water supply,the Cotter catchment, containing theBendora and Corin reservoirs. Before thefire, the Cotter supplied up to 96% of thewater used by the 350 000 people inCanberra and nearby Queanbeyan. Thenear pristine, heavily timbered catchmentprovided some of the purest water inAustralia, requiring minimal treatment.Now it’s a different story.

After the fires, the blackened Cotterlandscape, sitting right in the middle of thefire footprint, was a dismal sight. Although

pockets of vegetation only experienced aslow burn, the fire burnt through all theundergrowth and 35% of the catchmentsuffered a ‘very high-severity burn’ thatcompletely defoliated eucalypts and incin-erated the understorey and probably mostof the seed stores. The steep hill-slopessurrounding Bendora Reservoir experi-enced severe burning, as did riparian vegetation along the Cotter River.

Intense rain in March 2003 washed siltand debris into Bendora and authoritiesclosed the Cotter supply and, untilSeptember, switched to the alternative water

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There were severe but little-known effects from recentbushfires on essential watercatchments. Steve Davidsonuncovers a concerning story oflong-term damage and a lessonlearned about the vulnerability of our urban water supplies.

Burning issues for water supplies

The pristine Cotter River before the 2003 fires and (below right) the same river after the fires.

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supply, Googong Dam, in New South Wales.Googong has dropped to record low levelsand water restrictions apply. The Cotter hasalso been shut off several times since andwater drained from the bottom of Bendorato ease the build-up of sediments.

What were, and still are, the conse-quences of the fire in terms of watersupply? Professor Bob Wasson, then at theANU, Professor Paul Perkins of the ANUCentre for Resource and EnvironmentalStudies (CRES), and Ross Knee and TanyaWhiteway, both with Ecowise Environ-mental, say we are witnessing what happenswhen the ecosystem services provided bynatural vegetation in catchments are rudelyand suddenly removed. The fire reallyamounts to a large-scale, unplanned andunwanted ‘experiment’ in which almost anentire water-supply catchment has beenburnt in a natural catastrophe.

Ecosystem services sorely missedBefore the fire, the eucalypt forests, RamsarConvention1-registered sphagnum swampsand tussock grasslands of the Cotter catch-ment provided services that included: waterfiltration, erosion protection, water storage

(in sub-alpine swamps) andsequestering and storage ofcarbon and nutrients.Following removal of thevegetation, decline in waterquality in the reservoirs hasbeen dramatic and financialcosts to the communityimmediate.

A new treatment plant is being constructed atconsiderable expense tocounter the lower waterquality. It is expected thatrecovery of ecosystem services and water qualityto pre-fire levels will take at least 10 to 15 years.

The ACT State of theEnvironment Report, 2003,told of two post-fire thunderstorms that, in theabsence of healthy protec-tive vegetation, generatederosion over an area of18 square km, mobilising a massive 1314 to 2354tonnes of sediment persquare km. Wasson andseveral colleagues found that in the sixmonths following the bushfires, particulateorganic carbon and sediment dumped intothe upper Corin Reservoir were five to sixtimes the long-term average annual loads.In that short time, two storm episodesdeposited more than 2800 tonnes of sedi-

ment into Canberra’s water storages.Over most of the charred catchment,

the ground cover and much of the leaflitter have been removed by fire.Consequently, the magnitude of theerosion after just one rainfall event, onFebruary 8–9 last year, exceeded anythingexperienced there for some 400 years.And the pain will continue.

‘We know that there is a lot more sedi-ment and organic matter temporarilystored along the main stream channels,’warns Wasson. ‘This can be re-mobilisedand dumped into the reservoirs each timeheavy rain causes runoff and this willhappen despite gradual revegetation of hillslopes and stream banks.’

Mr John Dymke, Chief Engineer WaterOperations at ActewAGL, which operatesand maintains the ACT’s water and sewer-age assets, says there is concern about themassive turbidity (cloudiness of water) and the elevated concentrations of ironand manganese that have been docu-mented in the Cotter reservoirs. Elevatedlevels of iron and manganese can makewater taste bad and cause staining ofclothes during washing.

Another invisible but serious effect onwater supply following fire is the moisturetaken up by trees as they regenerate orgrow from seeds. Young plants absorb and

Over most of the charredcatchment, the ground coverand much of the leaf litterhave been removed by fire.

1 The international Convention on Wetlands – formally entitled ‘The Convention on Wetlands of International Importance, especially asWaterfowl Habitat’ – was signed at an international conference in the Caspian seaside town of Ramsar, Iran, in 1971. The treaty has been known informally by the name RAMSAR ever since. The name should be written Ramsar Convention.

Landsat images were used to map the 2003 fire severity.Bendora, especially, was badly affected.

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transpire large amounts of water duringactive growth, with this diminishing asgrowth plateaus in more mature trees.This has important ramifications for thehydrology of catchments because overlarge areas it means less groundwater flowto streams and dams. The growing treeseffectively pinch more water than would a mature forest.

Consequences and costsMr Asoka Wijeratne, General ManagerWater at ActewAGL, puts the cost ofupgrading water treatment plants to copewith ongoing water quality problems at$50 million. The works are due to becompleted by the end of this year.ACTEW Corporation is the owner andlicensed operator of Canberra’s watersupply, including all water-supply dams,while Environment ACT administers water resources and has land managementresponsibility in Namadgi National Park,which includes most of the Cotter catchment.

Rehabilitation Project Manager atActewAGL, Mr Peter Burgess, was unableto comment on the detail of fire manage-

ment strategies in thecatchment as the fires arethe subject of variousreviews and a CoronialInquiry. However, he isconcerned about the conse-quences of the fires.

‘Sadly, for the moment,the catchment has becomea net contributor ratherthan a barrier to waterquality problems,’ saysBurgess. ‘Due to the scale ofthe fire damage, we can’ttake much direct action tolimit erosion. Water yieldwill also be significantlylessened during vegetationrecovery over many yearsand this is a worry for thefuture water-supply security of the ACT.’

Paul Perkins, and nowan adviser to governmentson water policy, argues thatthe fact that bushfire consumed the entireCotter catchment suggests there is a realneed for improvement in land managementpractices. Burgess says that fire managementfor a quality water supply is not alwayscompatible with management for environ-mental or ecological values – something of aconundrum. The ACT Government isaddressing these issues as a priority underits recently released Water Strategy.

Dr Peter Cullen, of the CRC forFreshwater Ecology and Chair of the ACTNatural Resource Management Committee,

rejects the often-stated view that the 2003fires would not have started or would havebeen less catastrophic had National Parksand other conservation areas been regularlygrazed, periodically logged or frequentlyburned. He says there is no evidence tosupport this, and that the fires were anextreme event, probably a once-in-a-hundred-year occurrence. Indeed, the fireswere so intense that even paddocks withvirtually no grass carried flames.

‘Future fire management strategiesrequire careful balancing of a number ofcompeting objectives and a concretebunker approach to protection against firewould risk many every day values that weobtain from our natural resources,’ saysCullen. ‘Both wildfires and control burnsaffect runoff, erosion and other aspects ofcatchment hydrology, so managers need tobe well informed to select appropriate fireregimes.’

It seems likely that land managers whohave witnessed the extraordinary scale andintensity of the 2003 wildfires in south-eastern Australia will focus more on assess-ing the need for some degree of controlburning to reduce fuel loads in watersupply catchments.

In response to the fires, ACTEW and its partners have established a catchmentrehabilitation taskforce with the job ofcollecting comprehensive data as well ascatchment assessment and monitoring to assist in catchment remediation anddisaster planning.

The Cotter catchment about a month after the January 2003 fires, showing vegetationdenuded of foliage and bare soil, and sediments dumped in a creek following rain.

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Another invisible but seriouseffect on water supply followingfire is the moisture taken up bytrees as they regenerate or grow from seeds.

Australian Capital Territory water supply catchments.Bendora, Corin and Cotter are collectively known as the Cotter River catchment.

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Are the observed consequences of theCanberra firestorm typical of the impactthat fire has on water-supply catchments?In response to numerous requests forinformation from land and watermanagers, the CRC for CatchmentHydrology updated its website followingthe 2003 fires and provides answers to anumber of frequently asked questionsabout fire in catchments.

Hydrology of fireDr Emmett O’Loughlin, a former Directorof the CRC, who updated the website,reminds us that although fires caused bylightning are a natural occurrence inAustralia, and our resilient forests are accus-tomed to such events, in the short term, firecan have major consequences for watercatchments. These result because fire causes:

• temporary loss of vegetation and littercover

• release of nutrients into ash and nutrientloss to the atmosphere

• deposition of charcoal and ash on theforest floor

• changes to soil properties• altered biological processes• some permanent loss of mature trees• vigorous forest regrowth.

Scientists at the CRC say that, strangelyenough, because fire defoliates plants andso destroys the ability of vegetation to evap-orate water drawn from the soil, streamflow(baseflow) usually increases immediatelyafter fire, sometimes several-fold. This canhappen even in the absence of rain. Thewater that would normally be used by thevegetation adds to moisture in the deepersoil layers and some passes beyond therootzone and eventually into streams.

As long as evaporation from vegetationis suppressed, more and more water isstored in the soil during subsequent rain-fall events, the soil’s ability to act as abuffer during rainstorms diminishes andthis means more runoff can be expectedduring storms. So loss of canopy cover canresult in flood peaks several times greaterthan would occur in unburnt forest.

In the months (but not years) followingwildfire, catchments generally becomewetter than unburnt vegetated catchmentsuntil the foliage returns, and provide largerdry-weather flows and flood peaks untilvegetation (total leaf area) recovers.Furthermore, due to changes to the soilsurface, in the period shortly after fire, soilstend to shed water rapidly leading toincreased runoff during the first rains.

Commercial forestry in catchments and howthis relates to fire impacts and water suppliesis a contentious issue.

Professor David Lindenmayer, of the ANUCentre for Resource and EnvironmentalStudies, is a world authority on forest manage-ment. Living in Canberra, he experienced thefiery inferno of January 2003. Authorities in theACT are replanting most of the territory’s pine(Pinus radiata) plantations, which were inciner-ated in 2003, but is this the right way to go?Lindenmayer is adamant that it isn’t andsuggests we are repeating past mistakes.

‘Commercial softwood plantation forestryand quality water catchments just don’t mix,’he says.‘For a start, pines are killed outrightby wildfires and do not regenerate, whereasnative forests recover naturally.This meansthat, in the case of pines, after every wildfire –and there will inevitably be more – some orall of your forestry resource is wiped out.Thisis a huge financial loss.You also need toconduct costly salvage harvesting of thecharred trees and then replant.’

Lindenmayer would much rather seenative forests in water catchments, pointingto the water quality in Melbourne’s pristine

forested water catchment.The big plus is thatnative forests are fire adapted and recoverafter fire without need of human post-fireintervention. Fires devastate pines, butmerely disturb native forests and this distur-bance is actually beneficial to native forests,promoting habitat complexity, biodiversity,regeneration and productivity.

The forestry industry argues that pineplantations are more productive and prof-itable than eucalypt plantations or forestsand have recreational value. However,Lindenmayer suggests that the drawbacksshould be taken into account.

Apart from the financial costs, salvageharvesting is detrimental to catchmentsbecause the roads and soil disturbancecaused by machinery increase the risk oferosion and sediment movement intostreams and dams. Lindenmayer and severaloverseas scientists recently wrote in the jour-nal Science, that salvage harvesting activities,often undertaken as an urgent knee-jerk reac-tion, also undermine the benefits of fires,floods and other major natural disturbances inforests all over the world.Wildfires, for exam-ple, generate dead and downed trees, whichprovide habitat for many species, whereasthese are depleted by forestry practices.

A case in point was the salvage loggingafter the 1939 fires in Victoria, whichcontributed to a shortage of tree cavitiesused by more than 40 species of vertebrates,including the highly endangeredLeadbeater’s possum. Recovery from this sortof setback can take up to 200 years.

Native forests or forestry in catchments?

More information:Lindenmayer, DB, Foster, DR, Franklin, JF,Hunter, ML, Noss, RF, Schmiegelow, FA andPerry, D. (2004). Salvage harvesting policiesafter natural disturbance. Science 303: 1303.

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Fire rages through catchment forests nearCanberra.

In pine plantations, salvage logging and replanting after fire are expensive and damagingactivities.This is a view to a Mt Stromlo plantation.

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As evident in the Cotter catchment,these effects can be a mixed blessingbecause although the increased runoffduring storms, for example, may bringmore water into reservoirs, it also carriesan undesirable cocktail of soil particles,clay, charcoal, ash, nutrients and dissolvedorganic matter.

What about the longer term changes inhydrology wrought by fire? There are twobroad possibilities here.

Where forest trees are actually killed byfire (as in the case of many wet sclerophyll2

tree species), water yield can be reduced formany years, even decades. Assisted by thepool of nutrients released by the fire in theashbed, natural regeneration of the forestfrom seeds will lead to a young regrowthforest, with denser canopies than themature forest. These intercept more rainand transpire more water than the oldunburnt forest, less water reaches thestreams, and so the water yield is less.

However, where the fire does not kill thetrees outright, the pattern is different. Less-fire-sensitive forms of native forest usuallyrecover their leaf area within three to fiveyears. The water balance reverts prettymuch to its pre-fire behaviour after thattime. In catchments with a mix of thesebroad forest types, the long-term reduction

in water yield will be proportional to thearea of the former fire-sensitive forests.

Fortunately, the 2003 fires in south-eastern Australia occurred mostly in less-sensitive dry sclerophyll forests, and mostof the trees survived. According to the CRChydrologists, the water balance in most ofthe burnt catchments in south-eastAustralia should return to pre-fireconditions within about five years. In theCotter, the fire-sensitive Alpine Ash forests,that occur in pockets only, are an exceptionand until mature forest returns, theregenerating tree stands will depress wateryields, but only slightly due to their limiteddistribution. The severe drought is also acomplicating factor making life difficult for recovering species and for water supplyauthorities.

Where fire reduces the long-term secu-rity of water supply, in terms of eitherquantity or quality, for various water allo-cations, there will be pressure to reducereleases of water for environmental flowsand probably conflict between differentuser groups. This competition for waterwill be even greater in times of severedrought … and wildfire and drought often coincide.

Predictions of climate change (dimin-ished rainfall and higher temperatures)and the continuing risk of wildfires insouth-eastern Australia could combine to

reduce water quality and availability overthe next 25 years. The CRC for CatchmentHydrology warns that:

‘Maintenance of water supplies … willrequire a sea change in the way thatgovernment devises contingency plans forfuture water supplies. This will probablyrequire re-assessment of forest manage-ment policies in catchments, revision ofwater extraction licences from streams, andpossibly new (and larger) expenditure onwater storages. In conjunction with thesemeasures, it is inevitable that future waterdemand in cities will need to be restricted.’

For water consumers, both urban andrural, the Golden Age of apparentlyboundless water supplies seems to be over.We should never again take water forgranted. And living on a continentdescribed as the most flammable on Earth,it is imperative that we learn more aboutthe effects of fire on water-supply catch-ments and how to manage it wisely.

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Double silt booms at the top end of Bendora Reservoir, part of Canberra’s once-pristine watersupply catchment.

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More information:Wasson, R, Perkins, P, Knee, R and Whiteway,

T. (2003). Canberra Wildfire 2003, USGeological Society of America, Wildfiresand Watersheds Conference, Denver CO,USA, 2003.

Burgess, R, Dymke, J and Wade, A. (2004).Cotter Catchment remediation after theJanuary 2003 fires. AWA Enviro04Conference, Sydney, 2004

www.catchment.crc.org.au/bushfire/2 Sclerophyll forests: a typically Australian vegetation type having plants with hard, short and often spiky leaves. They occur in a band around

Australia from southern Queensland to the south-west of Western Australia. Wet Sclerophyll forests are taller than 30 metres, grow in higherrainfall areas and have a soft-leaved understorey, such as tree ferns.

Epicormic regrowth on eucalypts (foreground)contrasts with dead pines after bushfire.

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