Ecological effects of serial impoundment on the Cotter River, Australia

Susan Nichols*, Richard Norris, William Maher & Martin ThomseWater Cooperative Research Centre and the Institute for Applied Ecology, University of Canberra, ACT 2601, Australia(*Author for correspondence: Tel.: +61-2-62015408; Fax: +61-2-62015038; E-mail: sue.nichols@canberra.edu.au)

Received 22 September 2004; in revised form 15 November 2005; accepted 23 November 2005; published online 31 March 2006

Key words: serial impoundment, regulated river, biological assessment, macroinvertebrates, water quality,

AUSRIVAS, predictive model

Abstract

This study examines the ecological effects of serial impoundments (three dams) on a rocky upland stream insoutheastern Australia. Physical, chemical and biological changes were quantified and interpreted within athree-level hierarchy of effects model developed previously by Petts [1984, Impounded Rivers. John Wileyand Sons, New York] and the Australian Rivers Assessment System (AUSRIVAS) to predict pre-dam biota.First-order effects were decreased median monthly discharges and floods of lesser magnitude followingconstruction of the dams. No effect on water characteristics (pH, electrical conductivity and major ions) wasevident. The second-order effect on channel morphology was a decrease in bank-full cross-sectional area byup to 75% because of reduced flows. At all sites, the predominantly cobble streambed was armoured andgenerally highly stable. The discharge required to initiate movement of the streambed surface sediments(38.9 m3 s)1) was 40% less frequent since construction of the dams, implying alteration to the naturaldisturbance regime for benthic biota. Benthic algal growth appeared more prolific at sites directly belowdams. Fewer macroinvertebrate taxa than expected and modified assemblages within 1 km of all three damswere third-order effects. Compared to reference conditions, macroinvertebrate samples from the sitesdirectly below the dams had relatively more Chironomidae larvae, Oligochaeta and Acarina, and fewer ofthe more sensitive taxa, Plecoptera, Ephemeroptera, Trichoptera and Coleoptera. Biological recovery to themacroinvertebrate assemblage was evident within 4 km downstream of the second dam.

Introduction

Rivers are dammed and regulated for many rea-sons including water supply, irrigation and powergeneration. The purpose of the dam and the modeof reservoir operation (e.g., amount and timing ofreleases, off-take level) will influence the nature ofthe alteration to the natural river hydrograph andcharacteristics of the water downstream of theimpoundment. A regulated-river hydrograph mayshow a decrease in the median annual flow orchanges to the timing and magnitude of high andlow flows (King et al., 2003). Flow and waterquality changes have the potential for detrimentaleffects on river ecosystems (Poff et al., 1997;

Richter et al., 2003). A common concept is thatdownstream river ecosystems will recover from theeffects of regulation with increasing distancedownstream from the impoundment (Ward andStanford, 1983; Storey et al., 1991; Standford &Ward, 2001).

There is much literature on the effects of damsand other regulating structures but despite thisthere are few interdisciplinary studies on serialimpoundments (Ward & Stanford, 1979; Petts,1984; Walker, 1985; Growns & Growns, 2001; seereviews by Reid & Brooks, 2000, King et al., 2003and Lloyd et al., 2003). Further, most Australianstudies on the effects of river regulation have beenon lowland or sand-bed streams (Walker, 1979;

Hydrobiologia (2006) 572:255–273 � Springer 2006R.H. Norris, R. Marchant and A. Milligan (eds), Evaluation and Application of Methods for Biological Assessment of StreamsDOI 10.1007/s10750-005-0995-6

Thoms & Walker, 1992; Walker & Thoms, 1993).Kinetic energy and biotic features are known todiffer between these and higher energy, gravel-bedstreams. Consequently, a river’s response to regu-lation may also be expected to differ. In Australia,the high degree of flow regulation and recentgovernment reforms to address environmentalproblems (Cullen et al., 1996) provide the needand impetus for environmental water allocationsand the need to monitor and assess the ecologicaleffects.

A three-level hierarchy of effects from dams ispostulated by Petts (1984). First-order effectsoccur with dam closure and include changes towater quality, sediment load and flow regime.Second-order effects include changes to channelcross-section, bed-sediment movement and pri-mary production, as a consequence of first ordermodifications. Third-order effects, such as changesto macroinvertebrate communities and otherbiota, arise as a consequence of both first- andsecond-order effects. This ecosystem perspectivealso incorporates a temporal dimension because atime lag may exist between first- and third-ordereffects. Petts’ hierarchy provides a basis on whichto fashion a multidisciplinary study designed toevaluate the condition of impounded rivers with ahierarchy of cause and effect.

The physical, chemical and biological compo-nents of a river system interact with and areinfluenced by the catchment features to producethe first-, second- and third-order effects we ob-serve. There seems little sense in the investigationof single factors in isolation when all factors areoperating in conjunction (Petts, 1984). This paperaims to quantify the physical, chemical andbiological effects of a series of three dams on theCotter River, Australian Capital Territory.Therefore, we combine these single factors in ainterdisciplinary examination of effects of riverregulation within Petts’ hierarchical framework,which emphasizes the chemical, physical and bio-logical interactions involved.

Study area

The Cotter River has a catchment area of 482 km2

and is about 74 km long, flowing largely through asteep confined valley (Fig. 1). The Cotter River is

regulated by three dams; Corin, Bendora andCotter (Table 1). Granites are the dominant geol-ogy on the ridges of the catchment whereas Or-dovician sediments, mainly shales, sandstones andclays are present on the slopes (Owen & Wyborn,1979). This geological pattern is relatively uniformthroughout the catchment although minor volca-nic materials do occur in the river reach betweenBendora and Cotter reservoirs. The majority ofthe catchment (88%) lies within the NamadgiNational Park with land-use dominated by nativeforest although there is plantation forestry ofPinus radiata in the lower catchment. The climateis temperate, characterized by cold winters and hotsummers, with an average rainfall (1936–1993) of980 mm (Maddock et al., 2004). Maximummonthly rainfall occurs between August andOctober. There are significant water diversionsfrom the Cotter River, at Bendora Dam, for townwater supply and consequently the naturalhydrological regime has been altered. Meanannual flows have been reduced by over 30%below Cotter Dam and immediately downstreamof Bendora Dam median daily flows have beenreduced by 50–80% since the construction ofCorin and Bendora Dams in 1960s (Maddocket al., 2004).

The mode of operation differs for the threedams. Corin Dam (the upper dam) releases waterto the river channel to maintain water levels inBendora Reservoir. Thus, the river downstreammay have an altered flow regime but the annualvolume may change little. Water diverted fromBendora Dam (the middle dam) is supplied toCanberra via a gravity pipe and little water is re-leased to the river downstream. Cotter Dam (thelower dam) is essentially a large weir and there arefrequent unregulated flows, which overtops thespillway. Water is extracted from Cotter Damduring periods of high demand. Note that thisstudy was undertaken in 1997, and recently, envi-ronmental flows were introduced to the CotterRiver downstream of Bendora Dam (Maddocket al., 2004 and Chester & Norris this issue) butthis study uses data collected before their imple-mentation.

Given the mode of dam operation we mightexpect Corin Dam to have little effect downstreamunless the change of flow regime has had an effecton temperature regimes, nutrient concentrations

256

or timing of flows because the annual volume ofwater released to river channel should be similar tothe pre-regulation volume. Potentially, BendoraDam could have a significant effect because oflarge-scale water abstractions and the subsequentreductions in flows downstream. Corin and Ben-dora Dams both have multi-level off-takes but at

the time of this study may not have been managedto mitigate for cold-water pollution. Cotter Dam,essentially operated like a large weir, may beexpected to have had the least ecological effect butmight still display some detrimental effects result-ing from reduced flows caused by the operation ofBendora Dam and trapped sediment.

Figure 1. Location of test, reference and tributary sampling sites in relation to Cotter, Bendora and Corin Dams. The Cotter River

flows in a northerly direction.

257

Methods

Site selection and location

Our study was designed to provide a snapshot ofthe physical, chemical and biological condition ofthe Cotter River below each dam. Twenty-five siteswere selected to assess the effects of the threedams: Ten test sites along the length of CotterRiver, five reference sites in the surrounding re-gion, and ten tributary sites close to the CotterRiver (Fig. 1, Table 2). Limited access was possi-ble to the river between Corin and Bendora Dams,therefore, only two test sites within 1 km fromCorin Dam wall were sampled within that sectionof the Cotter River. Five test sites were selectedbetween Bendora and Cotter Dams to assess ef-fects and evaluate ecosystem recovery with dis-tance from the dam. One site was sampled withinthe short section (approx. 1 km) between CotterDam and the downstream junction of Paddy’sRiver, a major tributary and 2 sites sampled aboveand below Corin Reservoir (Fig. 1). Five referencesites with similar environmental features to thosein the Cotter River were selected for sampling.Environmental variables, used to match test siteswith reference sites by the AUSRIVAS predictivemodel (Coysh et al., 2000; Simpson & Norris,2000), were measured at each test site. The AUS-RIVAS model was then used to provide a list ofsites that could be expected to have similar faunato that of the test sites in the absence of possibleeffects of the dams. The reference sites were sam-pled in conjunction with the test sites to ensure

that the predictive model was actually detectingchanges in benthic macroinvertebrate communitiesassociated with the dams and not simply detectingenvironmental stress resulting from some regionalphenomenon.

Assessment of first-order effects

First-order effects influence the transfer of energyand material within the system (Petts, 1984).

HydrologyDischarge data for the Cotter River were notavailable before the construction of Cotter Dam,therefore, to determine the impact of flow regula-tion the discharge data for the period 1911–1960were compared to those between 1961 and 1996.The former is taken as the pre-regulation perioddespite the presence of Cotter Dam, which isessentially a large weir (Table 1) and as such willhave had minimal influence on the downstreamhydrology (Walker & Thoms, 1993). The latter isthe post-regulation period following the closure ofBendora Dam in 1961 and Corin Dam in 1969.Monthly hydrographs for the pre- and post-regu-lation periods were constructed to assess flowalteration downstream of Cotter Dam and inparticular to detect if flow regulation had influ-enced the seasonality of flows. Daily data werealso used to assess changes to the flow durationand frequency of floods in the pre- and post-reg-ulation periods.

Rainfall data (1938–1996) for four stationslocated throughout the catchment were analysed

Table 1. Characteristics of Cotter River reservoirs (Source: Fitzgerald, 1972)

Particulars Units Cotter Reservoir

1915–1950

Cotter Reservoir

after dam wall

made higher in 1951

Bendora

Reservoir

Corin

Reservoir

Year of completion 1915 1951 1961 1968

Spillway level Metres above sea level 494 501 779 956

Dam height Metres 14.9 22.2 42.7 70.7

Storage volume Gl 1.85 4.7 10.7 75.5

Surface area Hectares 28 51 75 298

Catchment area to upstream

dam or divide

Km2 192 93 197

Distance to upstream

dam or divide

Km 27 19 27

258

to assess for secular changes in annual rainfall andfor differences between the pre- and post-regula-tion period. Although annual rainfall is highlyvariable (CV’s 98.8–198.7% for the four stations)no secular patterns were ascertained. Indeed,average annual rainfall for the period 1961–1996(1023 ± SE 45 mm) was not significantly different(t = 1.3, d.f. = 50, p > 0.05) from that of 1938–1960 (932 ± SE 54 mm). Thus, given the minimalchanges in catchment land use, observed changesin the flow regime are assumed to result from thepresence of the dams and water extraction.

Water characteristicsSelected water characteristic variables were mea-sured from the riffle sections at each site and usedwith published data (Talsma & Hallam, 1982) toprovide an indication of whether impoundmentsinfluenced the nature of the water downstream.We acknowledge that cold or deep-water releasesmay potentially present problems below Corin andBendora Dams, this study was not designed toaddress this issue specifically by measuring watertemperature and dissolved oxygen (DO). Also,there is no published literature or previous data torefer to regarding the temperature or DO and levelof releases from Corin and Bendora Reservoirs(both of which have multi-level off-takes but at thetime of this study may not have been managed tomitigate for cold-water pollution). Thus, this studydoes not address the thermal pollution or DO as-pects of serial discontinuity but does investigatemacroinvertebrate assemblages that do integratevarious dam effects (including thermal effects andlow DO concentrations).

Electrical conductivity and pH were measuredonce when in the field at all sites using a HydrolabScout 2. A water sample was collected at each siteand kept on ice, until frozen for later microwavedigestion analysis for total nitrogen and totalphosphorus (Woo & Maher, 1995). Major cationswere determined by flame AAS (Varian-Tectron,1972) and sulphide and chloride by flow injectionanalysis with colorimetric detection procedures(Lachat, 1993a, b). Cation and anion values wereconverted to percentage milliequivalents andplotted (Piper, 1944) for comparative analysis.Conductivity and pH measurements were allo-cated to one of 4 site-groups, (1) sites within 1 kmbelow dams, (2) other Cotter River sites, (3)

reference sites (4) tributary sites and differencestested using analysis of variance and Tukey–Kramermultiple comparisons procedure which maintainedthe overall experiment-wise error rate at a = 0.05(SAS, 2003).

Assessment of second-order effects

Second-order effects relate to changes in channelstructure and primary production that result fromfirst-order modifications (Petts, 1984).

Cross-sectionsMonumented channel cross-sections below CotterDam, at Vanitys Crossing, and above Corin Res-ervoir at Gingera (Fig. 1) were resurveyed todetermine changes in river channel morphologysince 1954. Given the river channel is heavilyinfluenced by the presence of bedrock the presenceof flood debris, scour lines, changes in vegetationcomposition and differential lichen growth onrocks were all used to interpret post-regulationbankfull channel conditions.

SedimentsThree replicate bulk sediment samples were col-lected randomly from the riffle sections, at eachsite in the Cotter River, from within a 25 cmdiameter plastic-drum template. This was done toreduce the loss of fine sediment. Surface sedimentswere first removed, then the sub-surface sedimentwas collected to a depth of approximately 30 cmand the bulked replicate samples processed whilein the field. The surface and subsurface sedimentsamples were analysed separately and the textureof all samples were determined by passing themthrough a series of graded Wentworth sieves and aseries of standard sediment statistics calculated (cf.Briggs, 1977). In addition, the sediment-size datawere used to determine the armouring index, rel-ative bed stability and the initiation of motion ofsurface sediments (Gordon et al., 1992). Armour-ing refers to the coarse surface sediment layer thatoverlays the finer subsurface material and thearmouring index is merely the ratio of the mediangrain size of the surface sediment to the mediangrain size of the sub surface sediment. The relativebed stability (RBS) by comparison, refers to theability of the riverbed sediment to withstandmotion at a nominated discharge (Gordon et al.,

259

1992) whereas the initiation of motion is that dis-charge (m3 s)1) required to initiate movement ofthe riverbed sediment. For this study the sedimenttransport equation given by Bathurst et al. (1982)for coarse upland gravel-bed rivers was used.These data were combined with the discharge datafor the pre- and post-regulation periods to deter-mine the number of days there could have beenmovement or disturbance of the riverbed sedi-ments.

Periphyton and filamentous algaePercent cover of the substratum by periphyton andfilamentous algae was visually estimated at allCotter River and reference sites for both the rifflesampling site and the reach (i.e., 5 � the modebank-full width either side of the riffle samplingsite). Estimates were assigned to one of five fol-lowing categories, 1 = <10%, 2 = 10–35%,3 = 35–65%, 4 = 65–90% and 5 = >90%.

Assessment of third order effects

Third-order effects result from all first- and sec-ond-order modifications (Petts, 1984).

MacroinvertebratesMacroinvertebrates were sampled from riffle hab-itats at all Cotter River and reference sites andhabitat information collected using the standard-ized rapid biological assessment sampling tech-niques developed for the Australian NationalRiver Health Program (Davies, 1994; Parsons &Norris, 1996; Nichols et al., 2000; Simpson &Norris, 2000). Macroinvertebrates were sampledfrom a 10 m riffle transect, using a net with250 lm mesh and a base width of 350 mm inaccordance with these methods. Macroinverte-brates were preserved in the field using 10% for-malin, with Rose Bengal stain added to aidsorting. In the laboratory, preserved samples wererinsed placed in a sub-sampling box comprising100 cells (Marchant, 1989) and agitated untilevenly distributed. Contents of each cell were re-moved until approximately 200 animals from eachsample were identified (Parsons & Norris, 1996).Macroinvertebrates were identified to family tax-onomic level, except Chironomidae (to sub-fam-ily), Oligochaeta (class) and Acarina (to order),using keys listed by Hawking (1994).

To determine whether macroinvertebrateassemblages below dams had distinctly differenttaxonomic composition, compared to other CotterRiver and reference sites, we used a flexible clus-tering analysis (Beta = )0.1) and a Non-metricMultidimensional Scaling procedure (PC-ORD,McCune & Mefford, 1999) based on Bray-Cutisdissimilarities for presence/absence data at familytaxonomic-level. Three-dimensional ordinationsprovided a satisfactory summary of the data setsand Monte Carlo simulations (100 permutations)tested the significance of the stress level (p< 0.05).The taxa were then correlated with the ordinationaxis and taxa were considered important if theyhad significant Pearson correlations (p ‡ 0.05).

The biological health of Cotter River was as-sessed using the AUSRIVAS, A.C.T.-Autumn-Riffle, predictive model (Coysh et al., 2000;Simpson & Norris, 2000). The model, which isbased on the British RIVPACS models (Wrightet al., 1993; 1995), uses multivariate techniques tocompare test sites and groups of minimally im-paired reference sites. The model predicts themacroinvertebrate assemblages that are expectedto occur at sites in the absence of environmentalimpact (expected) and compares these with thosetaxa actually collected (observed). The predictivemodel allocates the observed over expected taxascores (O/E) to bands that provide an indication ofriver health. O/E values >1.12 are assigned toBand X (richer than reference), O/E values be-tween 0.88 and 1.12 are equivalent to referencecondition (Band A), values between 0.64 and 0.88are assigned to Band B (mildly impacted), O/Evalues 0.40–0.64 represent Band C (moderatelyimpacted) and Band D (severely impaired) are O/Evalues <0.40. For a detailed description of thepredictive model see Coysh et al. (2000) andSimpson & Norris (2000). Differences betweenO/E scores below dams (sites within 1 km fromdam wall) and other sites (Cotter River and Ref-erence) were tested for significance using singlefactor (3 levels) analysis of variance and Tukey–Kramer multiple comparisons procedure whichmaintained the overall experiment-wise error rateat a = 0.05 (SAS, 2003).

Macroinvertebrate relative abundance datawere also graphed to display assemblage struc-ture and macroinvertebrate sensitivity grades(SIGNAL, Chessman, 1995) were also used for

260

interpretation (10 = most sensitive to pollution,1 = most tolerant).

Results

First-order effects

HydrologyMedian monthly flows were markedly lower inthe post-regulation period compared to the pre-regulation period (Fig. 2). Since construction ofBendora and Corin Dams the mean daily averagedischarges immediately downstream were 1.43 and2.21 m3 s)1 respectively. On average median dailyflows in the post-regulation winter months (July–September) were 44.5% of those that occurred inthe pre-regulation period. Whereas median dailyflows in the post-regulation summer months(December–February) were 27.1% of those in thepre-regulation period. Overall there was a down-ward shift in the daily post-regulation flow dura-tion curve with flows that occur at least 90% oftime experiencing the greatest reduction (94.5%change). Less frequent flows also were markedlyreduced; for example those flows that occurred10% of the time were reduced by 32.8% in the postregulation. Indeed, the flood frequency analysis

revealed the magnitude of both smaller floodevents (i.e., those with an average recurrenceinterval of less than 2 years) to be reduced by 37%while larger magnitude flood events (those with arecurrence interval greater than 5 years) have alsobeen reduced in the post-impoundment period(Table 3).

Water characteristicsNo effects of the dams were evident from exami-nation of water quality variables investigated(Table 4, Fig. 3). The chemical composition of thetributaries and the Cotter River were similar, withno obvious changes in ionic composition at sitesbelow the three dams (Fig. 3). The order of dom-inance of major cations within the Cotter Riverand tributaries was Na+ > Mg2+ > Ca2+ >K+, except for Collins Creek (Na+ > Ca2+ >Mg2+ > K+). For anions the order of dominancewas mainly HCO3

) > SO42) > Cl), except Bimberi

Creek and Cribbs Creek where the order of aniondominance was SO4

2) > HCO3) > Cl).

Ionic balances indicated that major ions otherthan those considered were not present in appre-ciable quantities. No significant differences in pHvalues (Table 4) were detected among the site-type groups (F = 0.49; df = 3,21; p = > 0.05).Electrical conductivity values differed among site

0

1

2

3

4

5

6

7

8

Jan

Feb

Mar

ch

Apr

il

May

June

July

Aug

Sep

t

Oct

Nov

Dec

Month

Med

ian

disc

harg

e m

3 sec-1

Figure 2. Median monthly discharges recorded below Cotter Dam (Cotter Kiosk – Site 1) displaying reductions in monthly discharge

for periods 1911–1960 (Pre Bendora and Corin Dams) and 1969–1996 (Post Bendora and Corin Dams). h indicates Pre and n indicates

Post.

261

Table

2.Samplingsite

locationsanddescriptions,

Stream

order

(Strahler1952)derived

from

1:100000topographicalmap,DFS=

Distance

From

Source,

thepercent

CatchmentAreaRegulated(C

AR)represents

theproportionofasite’scatchmentareaim

pounded

(Petts,1980)e.g.,sitesdirectlybelow

damshaveaCAR

valueof100%

Locationcode

GRID

REF

Stream

order

Altitude(m

a.s.l.)

DFS(km)

Upstream

catchmentarea

(km

2)

Catchmentarea

regulated(%

)Map

H55

Reference

sites

PaddysR.(M

urraysCorner)

15

06

772

00

4550

36.0

231

0

60

844

00

CondorCK.(PadovansCrossing)

14

06

715

00

4600

13.0

43

0

60

887

00

CondorCK.(Brindabella

Rd)

13

06

694

00

4670

9.0

39

0

60

896

00

SawpitCK.(SmokersTrail)

12

06

720

47

2980

4.0

15

0

60

592

70

OrroralR.(O

rroralRd)

11

06

799

00

3880

16.0

87

0

60

515

00

Testsites

Cotter

R.(C

otter

Flats

aboveCorin

Dam)

10

06

654

96

41010

12.5

90

0

60

543

68

Cotter

R.(9

km

aboveCorinDam)

906

648

75

4980

19.5

125

0

60

574

57

Cotter

R.(500m

below

CorinDam)

806

664

00

4880

29.5

196

100

60

662

00

Cotter

R.(1

km

below

CorinDam)

706

664

00

4875

30.0

202

97

60

666

00

Cotter

R.(500m

below

Bendora

Dam)

606

660

08

4770

47.5

280

100

60

759

18

Cotter

R.(4

km

from

Bendora

Dam)

506

664

06

4700

53.5

330

85

60

791

08

Cotter

R.(onPipelineRoad)

406

692

63

4630

59.5

357

78

60

823

62

Cotter

R.(V

anity’sCrossing)

306

717

00

4580

66.0

363

77

60

867

00

Cotter

R.(Brack

sHole)

206

737

00

5530

71.0

472

59

60

891

00

Cotter

R.(700m

belowCotter

Dam)

106

764

00

5500

75.0

476

100

60

895

00

262

Tributary

sites

Pierces

CK.

T1

06

740

03

3590

11

0

60

876

62

LeesCK.

T2

06

698

26

3700

40

60

875

34

BushrangersCK.

T3

06

664

20

3690

50

60

793

53

CollinsCK.

T4

06

661

03

3720

50

60

775

82

CribbsCK.

T5

06

648

00

2990

40

60

583

41

MosquitoCK.

T6

06

623

02

21390

40

60

566

89

MckeahniesCK.

T7

06

624

01

21330

50

60

548

86

Littlebim

beriCK.

T8

06

660

92

21060

30

60

511

90

Bim

beriCK.

T9

06

656

39

21060

20

60

521

47

JacksCK.

T10

06

660

11

31070

60

60

499

76

263

groups (F = 05.76; df = 3, 21; p = < 0.05). TheTukey–Kramer procedure (a = 0.05) revealedsignificant differences between tributary sites andthe reference sites but no significant differencesbetween sites below dams, other sites in the CotterRiver and reference sites (Table 4). Nutrient con-centrations in the Cotter River and tributarieswere similar and low. At all sites in the CotterRiver total phosphorus (TP) was below methoddetection limits, <0.01 mg P l)1 and total nitrogen(TN) ranged between 0.04–0.16 mg l)1. Nutri-ent concentrations in the tributaries rangedbetween <0.01 mg l)1 and 0.03 mg l)1 for TP and0.01–0.25 mg l)1 for TN.

Second-order effects

Cross-sectionsComparisons of historical and contemporarychannel cross-section surveys suggested a reduc-tion in the bankfull cross-section area (Table 5).At Vanitys Crossing (Site 3) the bank-full cross-section area decreased by 75% (Fig. 4, Table 5).Field observations suggest this reduction inbankfull cross-section to be an accommodationadjustment – a contraction of the wetted channelrather than an active reduction in area through theaccumulation of sediment.

SedimentsRiverbed sediments in the Cotter River are char-acteristic of an upland boulder, cobble and gravel-bed river with a high degree of heterogeneity. Themedian grain size of the surface sediments rangedfrom )4.4 / to )6.2 / (/ is the Phi unit where/ = )log2 (mm)) and can be classified as either

coarse gravel or cobbles on the Wentworth scale.The riverbed sediments of the Cotter River alldisplayed armouring (Table 6) and as consequencehad relatively high bed stability indices, with theexception of Site 2, upstream of Cotter Reservoir(Table 6). Critical discharge required to initiatemotion at Site 1 (below Cotter Dam, Fig. 1) is38.9 m3 s)1 and flow records show the number ofdays per year that discharge exceeded this valuehave been reduced by about 40% since the con-struction of Bendora and Corin Dams (pre Ben-dora and Corin average = 3.5 d y )1,Post = 2 d y -1).

Periphyton and filamentous algaePeriphyton (10–35%) and filamentous algae (65–90%) covered most of the substratum at Site 6,below Bendora Dam. Below Cotter and CorinDams (Sites 1 and 7), between 35 and 65% ofsubstratum was covered by periphyton and <10%

Table 3. Cotter River flood frequency (pre and post regulation)

ARI Pre-regulation (1911–1960) Post-regulation (1961–1997) % change

1.05 10.45 2.92 72.05

1.11 13.62 6.12 55.06

1.25 19.40 13.54 30.20

2 42.60 26.75 37.20

5 116.35 109.28 6.07

10 191.15 167.30 12.47

20 314.56 214.37 31.85

Flows are instantaneous annual maxima (m3 s)1).ARI (average recurrence interval) as calculated via log Pearson probability distri-

bution.

Figure 3. Ionic composition of Cotter River and tributaries.

Coloured circles = Cotter River sites, open circles = Cotter

River tributary sites.

264

by filamentous algae. The only other Cotter Riversite to have algal growth similar to the sites belowdams was Site 3 (Vanity’s Crossing), whereperiphyton covered 35–65% filamentous algae10–35%. More algal growth was observed at thesesites compared to reference sites, which had0–10% of substratum covered by periphyton orfilamentous algae.

Third-order effects

MacroinvertebratesMacroinvertebrate assemblages below damsshowed a distinctive faunal composition comparedto other Cotter River sites and Reference sites(Figs. 5 and 6). The sites within 1 km of all 3 damsformed a distinct faunal group while other Cotter

River sites and Reference sites were similar to eachother (Fig. 5).

AUSRIVAS O/E scores indicated mild tomoderate impairment at sites directly below eachdam (Fig. 7). Between Bendora and Cotter Dams,where progressive downstream sampling was pos-sible, a recovery in biological condition (as indi-cated by the AUSRIVAS O/E score) was observedat Site 5, 4 km downstream of Bendora Dam(Fig. 5). Site 9 (above Corin Dam) and Site 11(located downstream of a picnic and recreationarea) appeared as mildly impaired. While thesesites had fewer than expected taxa, the presence ofmany sensitive taxa indicates good conditions(Fig. 8b). All other reference sites were equivalentto, or richer than, reference condition with regardto expected taxa (Fig. 7). Differences among site

Table 4. Conductivity and pH values (+SD) for Cotter River, Tributaries and Reference sites, sampled on June–July 1997

Site Electrical Conductivity lS cm)1 pH

Cotter River sites below dams 32.9 (12.8) 7.01 (0.12)

Cotter River sites (other) 36.8 (15.8) 7.05 (0.18)

Reference sites 60.4 (7.34) 6.85 (0.30)

Tributary sites 25.5 (18.7) 6.86 (0.50)

-1

0

1

2

3

4

5

6

0 3 5 9 10 11 14 16 18 20 22 25 29 32 37 42 46 49 55 56

Distance (m)

Met

ers

Present

Past

Past Bankfull

Present Bankfull

Figure 4. An example of reduction in bank-full cross-sectional area, Cotter River, Site 3 (Vanity’s Crossing).

265

groups in the O/E scores was significant (singlefactor ANOVA, F = 6.80; df = 2; 12;p = <0.05). The Tukey–Kramer procedure(a = 0.05) revealed that O/E scores were signifi-cantly lower at sites below dams but O/E values atreference sites and other Cotter River sites werenot significantly different from each other (Fig. 7).

All impaired sites below the dams were missingpredicted invertebrate families, Baetidae (may-flies), Leptophlebiidae (mayflies), Leptoceridae(caddisflies), and Psephenidae (beetle larvae), mostof which are assigned a high SIGNAL grade(Chessman, 1995) (Table 7). Additionally, the

more severely impaired sites below dams weremissing Simuliidae, Tipulidae (Diptera larvae),and Glossosomatidae (caddisflies). Note thatmany of these taxa are also listed as significantlycorrelated with the ordination axis (Table 8).Compared to reference conditions (at Sites 11, 12,13, 14 and 15) the invertebrate samples from theimpaired sites below the dams displayed relativelymore tolerant taxa, Chironomidae (midge) larvae,Oligochaeta (worms) and Acarina (water mites,Fig. 8a) and relatively fewer of the more sensitivetaxa (Plecoptera, Ephemeroptera, Trichoptera andColeoptera, Fig. 8b).

Distance (Objective Function)9.1E-03 1.7E-01 3.3E-01 4.9E-01 6.5E-01

Site001Site006Site008Site007Site002Site003Site014Site015Site004Site013Site005Site011Site009Site010Site012

Figure 5. Cluster analysis showing that sites below dams (Sites 1, 6, 7, 8) have a distinct faunal composition compared to other Cotter

River sites and the Reference sites (Sites 11, 12, 13 14, 15).

Table 5. Cross-sectional area, wetted perimeter and hydraulic radius at 3 sites on the Cotter River, ACT (cross-sections surveyed in

1954 and 1997)

Site Variable 1954 1997 % change

Below Bendora Dam (at Site 3)

Cross-sectional area (m2) 76.8 19.26 75 Reduction

Wetted perimeter (m) 67 20.5 69 Reduction

Hydraulic radius 1.15 0.94 18 Reduction

Below Cotter Dam (Site 1)

Cross-sectional area (m2) 37.6 11.5 69 Reduction

Wetted perimeter (m) 33.3 15.3 54 Reduction

Hydraulic radius 1.13 0.75 59 Reduction

Above Corin Dam (at Gingera)

Cross-sectional area (m2) 51 63.2 24 Increase

Wetted perimeter (m) 24.7 19.6 21 Reduction

Hydraulic radius 2.1 3.2 52 Increase

266

Discussion

Since the construction and operation of the CotterRiver dams median monthly flows have decreasedand the flow regime modified so that the smallerfloods are now suppressed, a first-order effect ofregulation (Fig. 2, Table 3). Low daily flows wereobserved belowBendoraDamandalso belowCorinDam where reservoir operation was expected tomaintain the annual discharge. First-order influ-ences of impoundments on water characteristicswere not observed for the major ion compositionand the other water variables measured. Thechemical composition of Cotter River samples wassimilar to the tributaries entering the Cotter River(Table 4, Fig 3). The order of dominance of majorions, ph, low conductivity and low nutrient con-centrations are consistent with the geology (gran-ites, Ordovician sediments), vegetation (forests) andland use activities of the catchment. Based on thestudy of Talsma & Hallam (1982), who measuredwater quality in the Cotter catchment weekly for5 years, our water quality data are representative ofwater quality throughout the year.

-1

0

1

-1

0

1

-1

0

1

Axis

3

Axis 1

Axis 2

Group 1 Below DamsGroup 2 Group 3

Figure 6. Macroinvertebate similarity of Cotter River and

References sites represented in a 3 dimensional solution by

Non-metric Multidimensional Scaling (stress = 0.0959). Sym-

bols represent the groups defined by cluster analysis (Fig. 5).

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

001 002 003 004 005 006 007 008 009 010 011 012 013 014 015

O/E

Rat

io Band B

Band D

Band C

Band A

Band X

Reference SitesCotter River Test SitesFigure 7. AUSRIVAS ACT–Autumn-Riffle predictive model observed to expected (O/E) taxa scores. Mean O/E scores below

dams = 0.68 (SD 0.10), at other Cotter River sites = 0.92 (SD 0.06) and Reference sites = 0.93 (SD 0.16). The bands represent

different levels of biological condition, Band X = richer than reference, Band A = equivalent to reference, Band B = mildly

impacted, Band C = moderately impacted and Band D = severely impaired. The arrows indicate sites directly below dams.

267

Second-order morphological change to a riverchannel requires sediment transport (Petts &Greenwood, 1985). The Cotter River is a confinedriver channel with little sediment input (until thebushfires of 2003), high boundary resistance, anarmoured streambed and overall there was littleevidence of gross change in the channel morphol-

ogy (Fig. 4). Abstraction of water from the CotterRiver for Canberra’s water supply has resulted incontraction of the active channel cross-sectionalarea (Table 5) (but not a change in shape) and thiswas evident at Site 3, well downstream of BendoraDam (Fig. 4). This second-order effect, caused bythe reduction in discharge volume (first-order

0

10

20

30

40

50

60

7000

1

002

003

004

005

006

007

008

009

010

011

012

013

014

015

Cotter River test sites

Perc

ent o

f sa

mpl

e

Acarina

Chironomidae

Oligochaeta

Reference sites

Reference sites

0

10

20

30

40

50

60

70

80

90

001

002

003

004

005

006

007

008

009

010

011

012

013

014

CotterRiver test sites

Pere

cent

of

sam

ple Trichoptera

Plecoptera

Ephemeroptera

Coleoptera

015

(a)

(b)

Figure 8. Relative abundance of macroinvertebrate taxa in riffle sections of the Cotter River and reference sites, June/July 1997.

268

effect) has resulted in reduced space for aquaticbiota.

A disturbance occurs to benthic stream com-munities when flow exceeds the threshold at whichsediment motion is initiated (Townsend et al.,1997). Reduction in the post-regulation frequencyof discharges sufficient to mobilize sediment(Fig. 2) has altered the disturbance regime in theCotter River (second-order effect). Disturbancetheory suggests that to preserve species richness,natural disturbances should be maintained (Con-nell, 1978; Begon et al., 1990). The prolific algalgrowth observed immediately downstream of thedams (particularly below Bendora Dam) resemblesthe effects of nutrient enrichment, however, lownutrient concentrations discount this cause. It islikely that extreme low flows and decreased dis-turbance frequency have contributed to more algalcovered substratum directly below the dams in theCotter River. This algal mat fills the substratuminterstitial spaces creating a more homogeneoushabitat for macroinvertebrates.

The spatial heterogeneity provided by thediversity of micro-habitats on a cobble substra-tum, free of prolific algal mats, may favour greatertaxonomic richness (Hynes, 1970) and any changesto the benthic algal conditions could also present achange in food resource (see Chester & Norris thisissue). The macroinvertebrate assemblages at thesites within 1 km downstream of the dams had adifferent invertebrate community structure and

less than the expected number of taxa compared toother Cotter River sites and reference sites (Figs.5–8, and Table 7). The conditions directly belowthe dams favoured taxa such as, Chironomidaeand Oligochaeta and disadvantage others likeSimuliidae, Psephenidae and Glossosomatidae(Table 7) that require fast-flowing water andsmooth, clean rock surfaces (see Hynes, 1970;Williams & Winget, 1979). The benthic algal con-dition and low flows could account for the inver-tebrate response and reduced macroinvertebratetaxonomic richness observed below each of theCotter River dams (Fig. 5) and these are commonresponses to impoundment (Armitage, 1979;Munn & Brusven, 1991; Growns & Growns, 2001;Chester & Norris this issue).

The effects on invertebrate assemblages wereconfined to sites immediately downstream of thedams where the percentage of catchment regula-tion ranged between 100 and 97% (Table 2 &Fig. 7). Observable effects on macroinvertebrateswere diminished at the site 4 km from BendoraDam (Site 5) where 85% of the catchment wasregulated. Invertebrate responses to flow regula-tion on the River Rede (also a upland river) werealso confined to areas where catchment regulationexceeded 92% (Petts et al., 1993). Macroinverte-brate assemblages were shown to recover belowthe Canning Dam in Western Australia in re-sponse to decreased regulation (Storey et al.,1991). Some studies suggest that the dam’s barriereffects, such as low recolonization rates, may bemore important for macroinvertebrate assemblagestructure than an altered flow regime (Marchant &Hehir, 2002). Our study cannot distinguish be-tween barrier and low-flow effects but it is feasible(given the algal and flow conditions) that barriereffects combined with sustained low flows were themajor factors controlling the abundance andrichness of invertebrate communities at siteswithin 1 km downstream of the Cotter Riverdams.

This study was not a long-term one but it hasdemonstrated that a hierarchical-effects frame-work including physical, chemical and biologicalindicators, which is based on a conceptual modelof how the ecosystem functions, is a useful toolfor evaluating the effects of river regulation andassessment of river health. The use of the frame-work has demonstrated that a interdisciplinary

Table 6. Armouring and relative bed stability indexes for

Cotter River sites

Site Armoured index Relative bed stability

1* 1.5 3.3

2 1.3 0.4

3 1.4 4.3

4 1.3 1.6

5 2.0 2.1

6* 1.4 1.7

7* 1.8 1.4

8* 1.6 1.6

9 1.5 3.1

10 2.0 3.1

Armouring index >1 = armoured; Relative bed stability

>1 = stable and <1 = unstable. Sites directly below dams are

indicated with an asterisk.

269

approach is needed to provide a more compre-hensive picture and evaluate the effects of thedams. The approach could be used to evaluate and

measure the ecological benefits of an alteredflow regime, such as that provided by environ-mental water allocations. The inclusion of the

Table 7. Taxa with ‡50% chance of occurrence, which are missing from sites assessed as impacted by the AUSRIVAS model

Taxa Sites

001* 006* 007* 008* 009 011 SIGNAL Sensitivity grade

Coloburiscidae X 10

Leptophlebiidae X X X X X 10

Hydrobiosidae X X X 9

Philopotamidae X X X X X X 9

Conoesucidae X 9

Elmidae X 8

Glossosomatidae X X X 8

Baetidae X X X X 7

Corydalidae X X X 7

Psephenidae X X X X X X 6

Tipulidae X X X 6

Gomphidae X X X 6

Simuliidae X X X X 5

Tanypodinae X 5

Hydroptilidae X X 5

Ecnomidae X X X 5

Caenidae X 4

SIGNAL sensitivity grades 1–10, where 10 = greatest sensitivity (Chessman 1995).Sites directly below dams are indicated with an

asterisk.

Table 8. Taxa showing significant Pearson correlations with ordination axes, N=15

Taxa Axis 1 Axis 2 Axis 3

Acarina )0.715

Amphipoda 0.715

Austroperlidae 0.731

Baetidae 0.711

Caenidae 0.555

Calocidae 0.830

Ceratatopogonidae 0.830

Corydalida )0.550

Elmidae 0.614

Hydrobiosidae )0.680

Leptoceridae 0.543

Leptophlebiidae 0.814

Lymnaeidae 0.611

Psephenidae 0.629

Scirtidae 0.637

Simuliidae )0.601 0.695

270

AUSRIVAS predictive models for biologicalassessment, which uses the reference conditionapproach (Reynoldson et al., 1997), may alsoprovide additional confidence in results wheresuitable control or reference-rivers are often scarcebecause the test sites are compared to the manyreference sites already sampled to build the pre-dictive model.

Because macroinvertebrates are representativeof the river’s condition over time they are consid-ered a more sensitive measure of river conditionsthan spot checks of chemical indicators. If the se-lected chemical indicators alone were examined,this study would have found no effects of regula-tion. If geomorphological indicators alone wereused, the Cotter River would have shown littlerecovery from the channel-contracting effects ofimpoundment. Abstraction for Canberra’s watersupply has altered the riverine environment andany future dam construction on the Cotter Riverwould probably exaggerate this situation. How-ever, the closed catchment management practicesthat ensure high quality drinking water, also pro-tect water quality for the aquatic ecosystem asindicated by the macroinvertebrate assemblages atsites other than those directly below the dams,where it seems altered flow conditions and/orbarrier effects, not water quality, have influencedbiota. The presence of algal mats, particularlybelow Bendora and Corin Dams, suggest thatthese sites could benefit from flushing flows thatcould create a scouring disturbance. The flushingflows should allow for natural seasonality in theflow regime, which should also meet the spawningrequirements of native fish.

Acknowledgements

We are grateful to A.C.T. Forests, National Parksand Wildlife Service and A.C.T. Parks and Con-servation for permission to conduct this studywithin Uriarra and Pierces Creek Pine Forests,Namadgi National Park and the MurrumbidgeeRiver Corridor. We also thank Frank Krikowa forundertaking the chemical analyses. The paper wasimproved by comments from David Williams,Paul Wallace, Donna Nunan, Nerida Davies andJulie Coysh. We acknowledge the 1997 3rd year

Water Science students from the University ofCanberra for their role in data collection.

References

Armitage, P. D., 1979. Stream regulation in Great Britain. In

Ward, J. V. & J. A. Standford (eds), The Ecology of Regu-

lated Rivers. Plenum Press, New York, 165–181.

Bathurst J. C., W. H. Graf & H. H. Cao, 1982. Initiation of

sediment transport in steep channels with coarse bed mate-

rial. Euromech 156: Mechanics of Sediment Transport,

Istanbul, Turkey, pp. 207–213, 12–14 July 1984.

Begon, M., J. L. Harper & C. R. Townsend, 1990. Ecology:

Individuals, Populations and Communities (2nd edn.).

Blackwell, Boston.

Briggs, D., 1977. Sources and Mthods in Gography: Sediments.

Butterworths, London.

Chessman, B. C., 1995. Rapid assessment of rivers using

macroinvertebrates – a procedure based on habitat-specific

sampling, family level identification and a biotic index.

Australian Journal of Ecology 20: 122–129.

Chester, H. & R. Norris, this issue. Dams and flow in the Cotter

River: effects on instream trophic structure and benthic

metabolism. Hydrobiologia.

Connell, J. H., 1978. Diversity in tropical rainforests and coral

reefs. Science 199: 1302–1310.

Coysh, J. L., S. J. Nichols, J. C. Simpson, R. H. Norris, L. A.

Barmuta, B. C. Chessman & P. Blackman, 2000. AUStralian

RIVer Assessment System (AUSRIVAS) National River

Health Program Predictive Model Manual. Cooperative

Research Centre for Freshwater Ecology, Building 15, Uni-

versity of Canberra, ACT, 2601. http://ausrivas.canber-

ra.edu.au/Bioassessment/Macroinvertebrates/.

Cullen, P., J. Doolan, J. Harris, P. Humphries, M. Thoms & B.

Young, 1996. Chapter 3: Environmental Allocations — the

Ecological Imperatives. In Managing Australia’s Inland

Waters: Roles for Science and Technology. A paper pre-

pared by an independent working group for consideration by

the Prime Minister’s Science and Engineering Council at its

fourteenth meeting, 13 September 1996, accessed 19/04/04

http://www.dest.gov.au/archive/Science/pmsec/14meet/in-

water/ch3form.html.

Davies, P.E. (ed.), 1994. Monitoring river health initiative.

River bioassessment manual. National river processes and

management program. (Freshwater Systems: Tasmania).

Fitzgerald, B. J., 1972. Fluvial sediment measurements and

investigations in the Australian Capital Territory. Com-

monwealth of Australia Department of Works Canberra

ACT. July 1972.

Gordon, N. D., T. A. McMahon & B. L. Finlayson, 1992.

Stream Hydrology: an Introduction for Ecologists. John

Wiley and Sons, Chichester, England.

Growns, I. & J. Growns, 2001. Ecological effects of flow reg-

ulation on macroinvertebrate and periphytic diatom assem-

blages in the Hawkesbury–Nepean River, Australia.

Regulated: Rivers Research & Management 17: 275–293.

271

Hawking, J. H., 1994. A Preliminary Guide to Keys and Zoo-

logical Information to Identify Invertebrates from Austra-

lian Fresh Waters. Cooperative Research Centre for

Freshwater Ecology Identification Guide No. 2. Cooperative

Research Centre for Freshwater Ecology, Albury, N.S.W.

Hynes, H. B. N., 1970. The Ecology of Running Waters. Liv-

erpool University Press, Liverpool.

King, A. J., J. Brooks, G. P. Quinn, A. Sharpe & S. McKay,

2003. Monitoring programs for environmental flows in

Australia — A literature review. Freshwater Ecology, Arthur

Rylah Institute for Environmental Research, Department of

Sustainability and Environment; Sinclair Knight Merz;

Cooperative Research Centre for Freshwater Ecology and

Monash University.

Lachat, 1993a. Quickchem Method 10-117-07-1-A. Chloride in

Waters. Lachat Instrument Company 66645 West Mill Road

Milwaukee W153218 USA, 1990.

Lachat, 1993b. Quickchem Method 10-116-10-1-c. Sulfate in

Waters Lachat Instrument Company 66645 West Mill Road

Milwaukee W153218 USA, 1990.

Lloyd, N., G. Quinn, M. Thoms, A. Arthington, B. Gawne, P.

Humphries & K. Walker, 2003. Does flow modification

cause geomorphological and ecological response in rivers? A

literature review from an Australian perspective. Technical

Report 2/2003, CRC for Freshwater Ecology.

Maddock, I., M. Thoms, K. Jonson, F. Dyer & M. Lintermans,

2004. Identifying the influence of channel morphology on

physical habitat availability for native fish: application to the

two-spined blackfish (Gadopis bispinosus) in the Cotter River

Australia. Marine and Freshwater Research 55: 173–184.

Marchant, R., 1989. A sub-sampler for samples of benthic

invertebrates. Bulletin of the Australian Society of Limnol-

ogy 12: 49–52.

Marchant, R. & G. Hehir, 2002. The use of AUSRIVAS pre-

dictive models to assess the response of lotic macroinverte-

brates to dams in south-east Australia. Freshwater Biology

47: 1033–1050.

McCune, B. & M. J. Mefford, 1999. Multivariate Analysis of

Ecological Data, Version 4.2 MjM Software. Gleneben

Beach, Oregon USA.

Munn, M. D. & M. A. Brusven, 1991. Benthic macroinverte-

brate communities in nonregulated and regulated waters of

the Clearwater River, Idaho, U.S.A. Regulated Rivers: Re-

search and Management 6: 1–11.

Nichols, S. J., J. L. Coysh, P. I. W. Sloane, C. C. Williams & R.

H. Norris, 2000. Australian Capital Territory (ACT),

AUStralian RIVer Assessment System (AUSRIVAS), Sam-

pling and Processing Manual. Cooperative Research Centre

for Freshwater Ecology, Building 15, University of Canb-

erra, ACT, 2601. http://ausrivas.canberra.edu.au.

Owen, M. & D. Wyborn, 1979. Geology and geochemistry of

the Tantangara and Brindabella 1:100 000 sheet areas. Bul-

letin of Mineral Resources, Australia, Bulletin 204: 52.

Parsons, M. & R. H. Norris, 1996. The effect of habitat-specific

sampling on biological assessment of water quality. Fresh-

water Biology 36: 419–434.

Petts, G. E., 1980. Morphological changes of river channels

consequent upon headwater impoundment. Journal of the

Institution of Water Engineers and Scientists 34: 374–383.

Petts, G. E., 1984. Impounded Rivers. John Wiley and Sons,

New York.

Petts, G. E. & M. Greenwood, 1985. Channel changes and

invertebrate faunas below Nant-Y-Moch dam, River Rhe-

idol, Wales, UK. Hydrobiologia 122: 65–80.

Petts, G., P. Armitage & E. Castella, 1993. Physical habitat

changes and macroinvertebrate response to river regulation:

the River Rede, UK. Regulated Rivers: Research and

Management 8: 167–178.

Piper, A. M., 1944. A graphic procedure in the geochemical

interpretation of water analyses. American Geophysical

Union Transaction 25: 914–923.

Poff, N. L., J. D. Allen, M. B. Bain, J. R. Karr, K. L. Pres-

tegaard, B. D. Richter, R. E. Sparks & J. C. Stromberg,

1997. The natural flow regime: a paradigm for river con-

servation and restoration. BioScience 47: 769–784.

Reid, M. A. & J. Brooks, 2000. Detecting effects of environ-

mental water allocations in wetlands of the Murray-Darling

Basin, Australia. Regulated Rivers: Research and Manage-

ment 16: 479–496.

Reynoldson, T. B., R. H. Norris, V. H. Resh, K. E. Day & D.

Rosenberg, 1997. The reference condition: a comparison of

the multimetric and multivariate approaches to assess water-

quality impairment usingbenthicmacroinvertebrates. Journal

of the North American Benthological Society 16: 833–852.

Richter, B. D., R. Mathews, D. L. Harrison & R. Wigington,

2003. Ecologically sustainable water management: managing

river flows for ecological integrity. Ecological Applications

13: 206–224.

SAS, 2003. SAS (r) 9.1 (TS1M3) SAS Institute Inc., Cary, NC,

USA.

Simpson, J. C. & R. H. Norris, 2000. Biological assessment of

river quality: development of AUSRIVAS models and out-

puts. In Wright, J. F. D. W. Sutcliffe, & M. T. Furse (eds),

Assessing the Biological Quality of Fresh Waters: RIVPACS

and Other Techniques. Freshwater Biological Association,

Ambleside, UK, 125–142.

Standford, J. A. & J. V. Ward, 2001. Arena revisiting the serial

discontinuity concept. Regulated Rivers Research and

Management 17: 303–310.

Storey, A. W., D. H. Edward & P. Gazey, 1991. Recovery of

aquatic macroinvertebrate assemblages downstream of the

Canning Dam, Western Australia. Regulated Rivers: Re-

search and Management 6: 213–224.

Strahler, A. N., 1952. Hypsometric (area–altitude) analysis of

erosional topography. Bulletin of the Geological Society of

America 63: 1117–1142.

Talsma, T. & P. M. Hallam, 1982. Stream water quality of

forest catchments in the Cotter Valley, ACT. In O’Loughlin,

E. M. & J. L. Bren (eds), The First National Symposium on

Forest Hydrology, 1982. Institution of Engineers Australia,

Canberra, 50–59.

Thoms, M. C. & K. F. Walker, 1992. Channel changes related

to low-level weirs on the River Murray, South Australia. In

Carking, P. A. & G. E. Petts (eds), Lowland Floodplain

Rivers: Geomorphological Perspectives. John Wiley and

Sons, Chichester, England, 236–249.

Townsend, C. R., M. R. Scarsbrook & S. Doledec, 1997.

Quantifying disturbance in streams: alternative measures of

272

disturbance in relation to macroinvertebrate species traits

and species richness. Journal of North American Bentho-

logical Society 16: 531–544.

Varian, Tectron, 1972. Analytical Methods for Flame Spec-

troscopy. Varian Pty Ltd, Melbourne, Australia.

Walker, K. F., 1979. Regulated streams in Australia: the

Murray-Darling system. In Ward, J. V. & J. A. Standford

(eds), The Ecology of Regulated Rivers. Plenum Press, New

York, 143–163.

Walker, K. F., 1985. A review of the ecological effects of river

regulation in Australia. Hydrobiologia 125: 111–129.

Walker, K. F. & M.C. Thoms, 1993. Environmental-effects of

flow regulation on the lower River Murray, Australia.

Regulated Rivers: Research and Management 8: 103–119.

Ward, J. V. & J. A. Stanford, 1979. Ecological factors con-

trolling stream zoobenthos with the emphasis on thermal

modification of regulated streams. In Ward, J. V. & J. A.

Standford (eds), The Ecology of Regulated Rivers. Plenum

Press, New York, 35–55.

Ward, J. V. & J. A. Stanford, 1983. The serial discontinuity

concept of lotic ecosystems. In Fontaine, T. D. & S. M.

Bartell (eds), Dynamics of Lotic Ecosystems. Ann Arbor

Science: Ann Arbor, 29–41.

Williams, R. D. & R. N. Winget, 1979. Macroinvertebrate re-

sponse to flow manipulation in the Strawberry River, Utah

(U.S.A.). In Ward, J. V. & J. A. Standford (eds), The

Ecology of Regulated Rivers. Plenum Press, New York,

365–376.

Woo, L. & W. Maher, 1995. Determination of phosphorus in

turbid waters using alkaline potassium peroxodisulphate

digestion. Analytica Chimica Acta 315: 123–135.

Wright, J. F., 1995. Development and use of a system for

predicting macroinvertebrates in flowing waters. Australian

Journal of Ecology 20: 181–197.

Wright, J. F., M. T. Furse & P. D. Armitage, 1993. RIVPACS –

a technique for evaluating the biological quality of rivers in

the UK. European Water Quality Control 3: 15–25.

273