4th Hydropower Forum - Mekong River Commission · Fish passes -monitoring Manual –Chapters 5.3.5 & 5.4 • Up-to-date, there are no best-practice examples of fish passes in large

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ISH0306 – Development of Guidelines for Hydropower Environmental Impact Mitigation and Risk Management in the Lower Mekong Mainstream and Tributaries

MRC tools and guidelines Fisheries Mitigation

Carina Seliger

4th Hydropower Forum 10 – 11 August 2017

Fisheries and Aquatic EcologyManual - Chapter 5

Mekong basin is a hotspot of biodiversity• >800 fish species - 2nd highest species richness in the world• High number of endemic species (~220)• High number of giant freshwater species• Several species important for local fisheries• >2/3 of rural LMB population are engaged in wild freshwater

fisheries

(FAO: Pangasianodon gigas)

Indi

rect

effe

cts

via

food

web

• Reduction in algae

• Reduction in macrophytes

• Reduction in benthic invertebrates

08.08.2017

Cascade of 5/11 Dams

River fragmentation

River fragmentation

• Change/loss of seasonal habitats

• Rapid habitat alterations (flow, velocities, temperature…)

• Alteration of sed./nutrient concentr.

• Blocked/ reduced fish migration

• Blocked/ reduced sediment transport

• Alteration of river dimension (depth, width)

• Alteration of quality/ quantity of habitats and hot spots

• Loss of passive drift

• Loss of key hydrol. events

• Alteration of shoreline areas and floodplains

• Loss of important habitats (deep pools, rapids…)

Impoundments• Seasonal flow

velocities• Sed. transport• Sed. flushing

Impoundments• Seasonal flow


Seasonal flow alterations

• Volume• Seasonality

(onset, duration)

• Min/max flows

Seasonal flow alterations

• Volume• Seasonality

(onset, duration)

• Min/max flows

Sub-daily flow alterations

• Characteristics of peaking



• Loss of important life cycle requirements/ triggers

• Stranding of larvae/eggs

• Loss due to flushing events

• Loss/ reduction of migratory species

• Loss of feeding areas

• Loss of spawning success

• Drift of small fish and larvae

• Reduction due to limited habitat availability

Fish

bio

mas

s an

d di

vers

ity

2nd order: Alteration of habitats and ecological

functions3rd order: Alteration of aquatic

biodiversity and biomass

1st order: Alteration of abiotic parameters

Hydropower risks Manual - Chapter 5.2.

III – Loss of connectivityIII – Loss of connectivity

IV –Impound-

ments

IV –Impound-

ments

I – Annual/ inter annualchanges to

flow


flow

II – Short-term flow

fluctuations/hydro-

peaking


fluctuations/hydro-

peaking

Chapter 5.2.1

Chapter 5.2.2

Chapter 5.2.3.5

Chapter 5.2.3

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River fragmentation

River fragmentation



• Sed./nutrient concentr.


• Blocked sediment transport

• River dimension (depth, width)

• Quality/ quantity of habitats (deep pools, rapids, hot spots)

• Support of passive drift

• Loss of ecological triggers

• Alteration of shoreline area and floodplains


Impoundment• Seasonal flow




Seasonal flow alterations• Volume

• Seasonality (onset,

duration)• Min/max flows








Indi

rect

effe

cts

via

food

web

• Loss of ecological functions (e.g. triggers)




• limited feeding areas

• reduced spawning success






Fish

bio

mas

s an

d di

vers

ity Sediment flushing

Fish pass

Minimum flow

Peaking limitations





No mitigation

Mitigation measures

Basin-scale management



IV –Impound-

ments

IV –Impound-

ments


flow


flow


fluctuations/hydro-

peaking


fluctuations/hydro-

peaking

08.08.2017


River fragmentation

River fragmentation



• Sed./nutrient concentr.


• Blocked sediment transport

• River dimension (depth, width)

• Quality/ quantity of habitats (deep pools, rapids, hot spots)

• Support of passive drift

• Loss of ecological triggers

• Alteration of shoreline area and floodplains
















Indi

rect

effe

cts

via

food

web

• Loss of ecological functions (e.g. triggers)




• limited feeding areas

• reduced spawning success






Fish

bio

mas

s an

d di

vers

ity Sediment flushing

Fish pass

Minimum flow

Peaking limitations





No mitigation

Mitigation measures

Basin-scale management



IV –Impound-

ments

IV –Impound-

ments


flow


flow


fluctuations/hydro-

peaking


fluctuations/hydro-

peaking

Complex ecosystem any change has an effect on the aquatic ecosystem & fisheries

• Habitat characteristics• Ecological functions • Food web

Master plans, dam sitingManual – Chapter 5.3.2.1

Potentially high impact related to the fragmentation ofmain migration routes

Dendritic Connectivity Index for migratory

species (DCImigr)

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Dendritic connectivity index for assessing theoverall connectivity loss

DCI m

igr [%

]

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Comparison of different scenarios


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(ICPDR, 2013)

Not only at dam site, but in entire impact section/ basin scale!

• Connectivity• Hydrology• Sediment delivery• …

Requires detailed knowledge on the system


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Hydropower capacity and river kilometres affected by fragmentation for different scenarios in the Coatzacoalcos Basin (Opperman et al., 2015)

Seasonal flow alteration (for storage HPs)Manual Chapters 5.2.1

Timing Duration

Magnitude

adapted from MRC 2009

limited habitatavailability, waterquality alteration

Ecological trigger (e.g. spawning)

Loss of seasonal habitats/ ecological functionsDecrease in productivity of LMB floodplains (incl. Tonle Sap and Great Lake System)

Arias et al. 2014

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(basin-wide coordination/ cooperation required!)

Downramping rate [cm/min]

Stra

ndin

g [%

]

decreasepeakincrease

Reference Peaking

increase

Drif

t [%

]

020

4060

Drift

[%]

No peaking Peaking

Indicators- Velocity of increase/ decrease- Dewatered area (peaking ratio)- Impacted length (downstream)

Sub-daily flow alteration/ PeakingManual Chapter 5.2.2

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- Downramping rate <5cm/h- Flushing (exceptional)

- Draw down <10cm/h- Filling <20cm/h

v <0.2 m/s)

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Impoundments/ Loss of connectivityManual Chapter 5.2.3

Sedimentation

Passive drift of eggs and larvae no longer supported if v < 0.2 m/s

Reduced passage efficiency

Turbine/ spillway mortality:- Small species: 2-15% turbine mortality- Large species: 35-80% turbine mortality

Flow velocity

Erosional wave & decoupling of floodplains

Large scale bypass systems

Bypass channels/ rock ramps

Fish pass facilities

Upstream Downstream

Vertical slot fish passes

Protection Downstream fish pass

Rakes/ Screens Bypasses

Spill flow Adapted turbines

Open gates

Connectivity restoration at the damManual Chapters 5.3.2.2 & 5.3.3.1

Adapted schemes/ operation

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Fish passes - monitoringManual – Chapters 5.3.5 & 5.4

• Up-to-date, there are no best-practice examples of fish passes in large tropical rivers.

• Most of current knowledge on fish pass functioning and fish migration behaviour have been gained from fish pass monitoring programmes filling of knowledge gaps!

• Monitoring at Xayaburi and Don Sahong will bring additional insights

• Assessment of current bottlenecks/ shortcomings and adaptive management has to guide the way for future developments

08.08.2017

Monitoringbefore, during and after

construction

Fish passes - monitoringManual – Chapters 5.3.5 & 5.4

Fish passage functioning • overall passage efficiency of individuals or species at fish passes,

• i.e. proportion of individuals successfully passing a fish pass or number of species within a community observed passing a fish pass (Larinier, 2000, Castro-Santos et al., 2009; Roscoe & Hinch, 2010).

Cumulative passage efficiency• up- and downstream migration (cumulative barrier passage!)

• Three phases: attraction, passage itself and post-passage effects

Population functioning• Completion of full life cycle: spawning, egg/larval, juvenile, adult incl.

migrations

• Maintaining a minimum population size

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Alternative schemes layouts/operationsManual – Chapter 5.3.2.2

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(Assessment at Xayaburi)

e.g. Pak Mun Dam

- Avoids high losses related toturbine passage

- Supports passive drift of eggsand larvae

(Annandale 2014)

Dam height: 54mDam length: 18kmImpoundment: 80km

suitable fish pass solution questionable

Disconnection of 3S system!

Partial barrageManual – Chapter 7.3.3.5

Dam height: 54mDam length: 18kmImpoundment: 80km

(Annandale 2014)

Dam height: 20mDam length: 2.9kmImpoundment: 35km

fish pass or guiding system required

possibly 2nd fish pass at diversion weir required

sufficient flow (attraction, depth)

guiding systems

suitable fish pass solution questionable

prior assessment of migration routes/ preferenes

Partial barrageManual – Chapter 7.3.3.5

Recommendations for future investigations

Planning of efficient mitigation measures requires detailed knowledge on the system!• Identification of research needs related

to fisheries and aquatic ecology

Monitoring should focus on • guild/ species-specific reaction to pressures• life cycle assessment• important habitats• important ecosystem functions

08.08.2017

Thank you for your attention!

Carina SeligerInstitute of Hydrobiology and Aquatic Ecosystem ManagementUniversity of Natural Resources and Life Sciences Vienna

Gregor-Mendel-Strasse 33, A-1180 ViennaTel.: +43 1 47654-81218, Fax: +43 1 [email protected]/ihg

Documents

4th Hydropower Forum - Mekong River Commission · Fish passes -monitoring Manual –Chapters 5.3.5 & 5.4 • Up-to-date, there are no best-practice examples of fish passes in large