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A WATER FRAMEWORK DIRECTIVE (WFD) COMPLIANT DETERMINATION OF ECOLOGICALLY ACCEPTABLE

FLOWS FOR ALPINE RIVERS IN AUSTRIA

A. ZITEK1 , P. JÄGER2, B. ZEIRINGER3

1 EcoScience, Environmental Studies, Goldschlagstraße 209/6 1140 Vienna,

Email: [email protected] Ingenieurbüro für Ökologie und Umweltbiologie

Brunn 147, 5201 Seekirchen am Wallersee, AustriaEmail: [email protected]

3 Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences, Vienna, Austria

Email: [email protected]

Content

• Study area• Aim of the study• Residual flow assessments

• Methods• Results

• Conclusion

Mur

Salzach

Study sites in Salzburg -Austria

Water abstraction sites at 20 power plants at mainly wadeablerivers at 63 river stretches (40 water abstraction sites, 23 full water sites),

Residual flow < MALFResidual flow > MALF

Hydropeaking < 1:5

Hydropeaking > 1:5

Characteristics of the assessedriver stretches

Slop

e%

Aim of the study

• Evaluation of the existing hydromorphologicalsignificance criteria used to pre-classify the currentecological status of rivers with regard to the EU Water Framework Directive formacrozoobenthos and fish with regard to:•• EcologicallyEcologically acceptableacceptable minimumminimum flowflow at at waterwater

abstractionabstraction sitessites

•• Central Central questionquestion: : cancan thethe good good ecologicalecologicalstatusstatus ((WFDWFD--terminologyterminology) ) cancan bebeachieved/maintainedachieved/maintained whenwhen usingusing thisthissignificancesignificance criteriacriteria ??

Methods

Structure of the residual flow assessmentSignificance criteriaSignificance criteria

• Ecologically acceptable flow > Natural absolute daily minimum flow (nat. ADMF)

• MALF residual > MALF (as total annual discharge load)

Testing for ecological relevance – is more water needed?

• Fish ecological judgement using Fish Index Austria

• Macrozoobenthos,

• Hydraulic habitat analysis

• Habitat modelling

Testing and validating additional parameters to define the ecologically acceptable flow

• Maximum depth in the cross section of the minimum (“pessimum”) riffle

• v_mean in the cross section of the pessimumriffle

• Mean thalweg depth

• Residual pool depth as a measure for morphology

Additional parameters for determiningecologically acceptable minimum flow

≥ 0,30,600,40≥ 0,30,30Epipotamal

≥ 0,30,500,30 (0,402)≥ 0,30,20 (0,302)Hyporhithral

≥ 0,30,300,30≥ 0,30,20Metarhithral

≥ 0,30,250,25≥ 0,30,20Epirhithral (≤ 3% Gefälle)

≥ 0,30,200,20≥ 0,30,15Epirhithral (3-10% Gefälle)

≥ 0,30,150,15≥ 0,30,10Epirhithral (> 10% Gefälle)

Leitströmung imWanderkorridorvmin [m/s]

Zur Laichzeit:ØMindesttiefe (1)TLZ [m]

Zum Erhalt des Lebensraumes: Ø MindesttiefeTLR [m]

Mindestfließ-geschwindigkeitvmin [m/s]

Mindestwasser-Tiefe Tmin [m]

Für den TalwegFür den Bereich der Schnelle

Fließgewässerzone

≥ 0,30,600,40≥ 0,30,30Epipotamal

≥ 0,30,500,30 (0,402)≥ 0,30,20 (0,302)Hyporhithral

≥ 0,30,300,30≥ 0,30,20Metarhithral

≥ 0,30,250,25≥ 0,30,20Epirhithral (≤ 3% Gefälle)

≥ 0,30,200,20≥ 0,30,15Epirhithral (3-10% Gefälle)

≥ 0,30,150,15≥ 0,30,10Epirhithral (> 10% Gefälle)

Leitströmung imWanderkorridorvmin [m/s]

Zur Laichzeit:ØMindesttiefe (1)TLZ [m]

Zum Erhalt des Lebensraumes: Ø MindesttiefeTLR [m]

Mindestfließ-geschwindigkeitvmin [m/s]

Mindestwasser-Tiefe Tmin [m]

Für den TalwegFür den Bereich der Schnelle

Fließgewässerzone

Pessimum riffle Thalweg

Mean depth(m)

Mean depthspawningtime (m)

Minimum flow vel.

(m/s)

Minimum depth

(m)

Minimum profile flowvel. (m/s)

River region

slope

slope

slope

Measurement & sampling design

Macrozoobenthos (Saproby and species specific analysis)

Lower end of residual flow stretch

Upstream water abstraction

Upper end of residual flow stretch

Downstream water abstraction

Fish ecological status (Fish Index Austria)

Hydraulic & habitat mapping

Measurements at 200 m sections

Discharge

Wetted width

Maximum depth pessimum riffle

Mean Profile flow velocity at pessimum riffle

Pool depths (n=5)

Riffle depths (n=5)

=> Mean thalweg depth

At three discharges (< MALF, MALF, > MALF)

Additional measurementsWidth at MAF Bankfull widthLocal slope

Standard residual flow assessmentStandard residual flow assessment(Guideline for defining ecologically acceptable (Guideline for defining ecologically acceptable

flow, Salzburg, flow, Salzburg, JJäägerger et al. 2008)et al. 2008)

KW Maria Sorg Restwasserstrecke

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

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

Q [m³/s]

Tmin

[m]

Hydraulic signatures for ecological modelling at different scales, Yann Le Coarer, Aquatic Ecology (2007) 41:451–459

Hydraulic mapping mapping Hydraulic mapping mapping (after (after ParasiewiczParasiewicz, 2007), 2007)

Target: systematic and stratified assessment of depth-flow velocity patterns at different discharges- Hydro-morphological units HMU) for orientation and stratification (7-15 measurements per HMU).

Characterisation of Characterisation of instreaminstream sediment sediment incl. qualitative assessment of incl. qualitative assessment of embeddednessembeddedness and proportion of fines, and proportion of fines, instreaminstream structures (different types structures (different types -- no, no, existing, abundant), shoreline structure existing, abundant), shoreline structure and land useand land use

Pressure/Site Site 1 Site 2 Site 3 Site 4Water abstractionHydro-peakingMorphological changeTemperature changeImpoundmentConnectivity lossEmbeddednessCatchment Land useSediment flushingWater quality

Identification of pressure combinations and main pressures

0

2

4

6

8

10

12

14

16

18

20

01.01

.2003

01.02.20

0301

.03.200

301

.04.20

0301.0

5.2003

01.06

.2003

01.07

.2003

01.08.20

0301

.09.200

301

.10.20

0301.1

1.2003

01.12.2

003

Date

Dis

char

ge [m

³/s]

Qresidual

Qdefined

Daily mean discharge at abstraction site

Is this enough to fulfil ecological requirements?

Constructing the hydrograph at water abstraction sites

Turbine uptake capacity

Natural minimum flow

Main resultshydraulicmapping

Results hydraulic mapping: Changes of flow velocity distributions with

decreasing discharge

Reducation of substrate movingdischarges (MAF+20%)

KW Spannberg 2003 Wasserfassung

Vergleich natürliche Jahresganglinie mit Jahresganglinie in Ausleitung

0

2

4

6

8

10

12

14

16

18

20

01.01

.2003

31.01

.2003

02.03

.2003

01.04

.2003

01.05

.2003

31.05

.2003

30.06

.2003

30.07

.2003

29.08

.2003

28.09

.2003

28.10

.2003

27.11

.2003

27.12

.2003

Datum

Dur

chflu

ss [m

³*s-1

]

Tagesmittel anWasserfassung

QKons

Qrest1

MQ+20%

Zeit MQ+20%

Dynamic discharge in residual flow stretches

KW Winkler 2003 Wasserfassung


0

2

4

6

8

10

12

14

01.01

.2003

31.01

.2003

02.03

.2003

01.04

.2003

01.05

.2003

31.05

.2003

30.06

.2003

30.07

.2003

29.08

.2003

28.09

.2003

28.10

.2003

27.11

.2003

27.12

.2003

Datum

Dur

chflu

ss [m

³*s-1

]


QKons

Qrest

MQ+20%

Zeit über MQ+20%

KW Winkler 2004 Wasserfassung


0

2

4

6

8

10

12

14

01.01

.2004

31.01

.2004

01.03

.2004

31.03

.2004

30.04

.2004

30.05

.2004

29.06

.2004

29.07

.2004

28.08

.2004

27.09

.2004

27.10

.2004

26.11

.2004

26.12

.2004

Datum

Dur

chflu

ss [m

³*s-1

]


QKons

Qrest

MQ+20%

Zeit über MQ+20%

After After flushingflushing

FlushingFlushing of of sedimentssediments fromfromimpoundmentsimpoundments

DuringDuring flushingflushing

DuringDuring flushingflushingBeforeBefore flusingflusing

Reduction of substrate movingdischarges (MAF+20%) and percentage

of area with medium/high fine sedimentsFi

nes

in s

edim

entm

ediu

m/h

igh

(% o

f tot

al a

rea

map

ped)

Reduction of days with sediment moving discharges

Summary results hydraulicmapping

• At ADMF the highest flow velocity classes were lost in most situations – maintained above MALF.

• Below ADMF flow velocities between 0,0 – 0,4 became dominant– loss of river type specific flow variability and habitats.– increased sedimentation of fines and

• Below ADMF a significant loss of wetted width in relation to the wetted width at MALF leading to significantly reduced ecologically available wetted habitats.

• Below ADMF limits for connectivity for fish like maximum depth at the pessimum profile and minimum flow velocity in thalweg are undercut – sometimes these parameters require more water to be fulfilled!

Main resultsbiology

Relationship between slope and fish biomass

(Spearman-Rho, r=-0,469**, p=0,000). (Spearman-Rho, r=-0,364**, p=0,005)

HydraulicHydraulic stress as stress as factorfactorhighlyhighly negativelynegatively correlatedcorrelatedwithwith fishfish biomassbiomass

Changes in length-frequencydistributions of brown trout

All age classes!

2

3

Mean length and mean weight of brown trout at natural and

residual flow sitesNatural

dischargeResidual

discharge

I

Residual discharge

II

Natural discharge

Natural discharge

Residual discharge

I

Residual discharge

II

Natural discharge

Ecol

. Sta

tus

high

<-F

ish

Inde

x A

ustr

iaju

dgem

ent-

> ec

ol. S

tatu

s ba

d

Fish ecological judgement of river sitesreleated to type of pressure

goodgood

moderatemoderate

Biotic characteristics in significantlyabstracted sites with good ecologcial status

VarianceVariance of of fishfish lengthlength

Good (n=7) Moderate or worse (n=13)

JudgementJudgement of of lenghtlenght--frequencyfrequency distributiondistribution


BiomassBiomass


Abiotic parameters explaining the good ecological status at significantly abstracted sites


MeanMean waterwater depthdepth MeanMean subtsratesubtsrate sizesize



Relative Relative roughnessroughness

35 % of significantly abstractedsites with good ecological status

• Situated in smaller and steeper rivers, with two of them being situated at the upper end of the fish bearing zone.

• Situated within the trout region with brown trout being the only dominant species.

• Larger mean choriotope size lead to higher values of relative roughness -> habitat heterogeneity -> different size classes of trout -> higher variance of fish lengths -> better judgement of the age distribution.

• The biomass was always considered as satisfyingand biomass KO criterion was never actuated.

Results Macrozoobenthos –reduction of rheophilous species

Num

bero

f rhe

ophi

lous

taxa

Abstraction sites (n=13) Reference (n=10)N

umbe

rof r

heoh

ilous

and

rheb

iont

taxa

Abstraction sites (n=13) Reference (n=10)

Saproby Index failed to assess the impact of waterabstraction on ecological status!

Conclusions• ADMF represents a valid base for determining the ecologically

acceptable base flow -> additional parameters help to maintain important functions like connectivity.

• Experiences: in steep alpine rivers in some cases its hard to reachthe cut value for minimum depth (15-20 cm), in lowland rivers thetrend goes to discharges bigger ADMF to maintain flow velocitiesand depth, some types of rivers show a trend to decreasingminimum flows (climate change) which also needs to beconsidered adequately – next step is regionalisation!

• ADMF = a natural catastrophic event -> a dynamic component to this minimum base flow to maintain the river type specific flow variability is recommended, contributing to the maintenance of natural geomorphologic (e.g. sediment quality) and ecological processes linked to natural flow patterns.

• ADMF and hydromorphological cut values implemented in National Water Act for WFD!

Thank you for your attention!Thank you for your attention!

[email protected]

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