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

Mekong River Commission

Office of the Secretariat in Vientiane 184 Fa Ngoum Road, Ban Sithane Neua, P.O. Box 6101, Vientiane, Lao PDR Tel: (856-21) 263 263 Fax: (856-21) 263 264

Office of the Secretariat in Phnom Penh 576 National Road, no. 2, Chok Angre Krom, P.O. Box 623, Phnom Penh, Cambodia Tel: (855-23) 425 353 Fax: (855-23)425 363

mrcs@mrcmekong.org www.mrcmekong.org

Guidelines and Recommendations for Mitigation of Hydrological and Flow Impacts

Kees Sloff and Jenny Pronker

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What will you learn?

• The ISH0306 approach

• Know your basin

• Risks, impacts and vulnerabilities of HP development

• Using the mitigation hierarchy

• From individual schemes to a joint operation of multiple

schemes

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About your ISH trainers for these 2 sessions

Kees Sloff • PhD on reservoir sedimentation in 1997

• Deltares since 1995: specialist

• Assistant Professor at Delft University since 2001

Jenny Pronker • MSc Civil Engineering 2017

• Thesis on Impacts of Hydropower on the Mekong Delta

• Starting at CDR International next month

Lois Koehnken

• PhD Sediment transport in the Orinoco River Basin in 1990

• Director L Koehnken Pty Ltd, Australia

• Sediment speciailist in several MRC programs

kees.sloff@deltares.nl c.j.sloff@tudelft.nl

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Introduction to Mitigation

• HPPs have the potential to directly alter flow and sediment movement in river systems

• Rivers will respond to these changes, and these responses may have negative impacts with respect to:

- The physical integrity of the river

- The ecology of the river

- The social uses of the river

• Ideally negative impacts are avoided but this is rarely possible

• When negative impacts cannot be avoided, need to minimise and mitigate

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Consider the ‘life cycle’: each dam will influence the river for generations

• Many dams are built to exist for a century

• Impacts will last at least 4 generations, and probably even beyond that (even if dam is removed)

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A HPP scheme is just an element of the system or basin: impacts extend basin wide

http://cmsdata.iucn.org

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The ISH0306 approach

• Hydrology and flows

Guidelines and Recommendations for

Mitigation of Hydrological and Flow Impacts

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Step 1: know your system – Hydrology of the Mekong

• Monsoon June – Nov

• Dry season

• Lot of rain in the Eastern Lao catchments

• Timing of start and end of wet season is very regular (2 weeks variation)

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Step 1: know your system – Hydrology of the Mekong

• Lancang (China) only contributes 16% to average annual flow

• Effect China more relevant in Vientiane than Kratie, and more relevant in dry season

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Step 1: know your system: establish baseline

• Collect your required data

- Historic data

- Targeted surveys (install your equipment)

- Remote sensing data (inundated areas, etc)

• Complete assessments using models (computational, physical)

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Step 2: risks, impacts, vulnerabilities of HP development

Evaporation/rain

Rainfall

to runoff

River runoff

hydrograph

modified

hydrograph

Salinity

intrusion

cascade

Tributary run off

Evaporation/rain Storage

Tributary run off

Storage

Tonle

Sap

Lancang

Dams

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• For impacts on hydrology and flow the ‘reservoir’ and how it is operated is more relevant than the dam

ponce.sdsu.edu

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Step 2: risks, impacts, vulnerabilities of HP development: ‘storage’ versus ‘run-of-the-river’

• Storage reservoirs (often high dams) are used to capture the fluctuations in the inflow discharge: downstream of such dams the flow is more constant (reduced high flow, increased low flow)

Nuozhadu dam, Lancang: storage

Xayaburi dam: run of the river

• Run-of-the River reservoirs (often low dams) operate with a more-or-less constant water level: all incoming discharge is going through the turbines and spillways. Downstream no impacts.

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Step 2: risks, impacts, vulnerabilities of HP development: values and risk

• Understanding values & risks – What needs to be protected

after HPP development?

• Hydrology and flows examples:

- Physical: Timing of onset of wet season; Tonle Sap reversal;

inundation depth and inundated areas of flood plains; …

- Ecological: Sustain wetlands; trigger for fish migration; deep

pools; …

- Social: availability of clean fresh water; tourism; navigability;

…

Fis

hbio

.com

laotiantim

es.c

om

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Importance and value of flow in the Mekong basin What needs to be protected after HPP development?

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Annual / inter-annual changes to flow

Changes in seasonality &

continuous uniform release

Change of timing & duration of floods and low flows, changes in flows Tonle Sap and changes in salt intrusion in the delta

Modification of flood

intervals: Reduction in

occurrence of minor floods

& no change in large events

Peaks in flood and low flow

change, smoother hydrograph

Daily / short-time period changes in flow

Hydro-peaking Safety and navigation related

changes caused by sudden rise

or drop of water levels

Pulses by operations idem

jan dec

flow

jan dec

flow

Secondary (indirect) risks through impacts on sediment

movement, fish, navigation, water quality

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Annual / inter-annual changes to flow

Changes in seasonality &

continuous uniform release

Change of timing & duration of floods and low flows, changes in flows Tonle Sap and changes in salt intrusion in the delta

Modification of flood

intervals: Reduction in

occurrence of minor floods

& no change in large events

Peaks in flood and low flow

change, smoother hydrograph

Daily / short-time period changes in flow

Hydro-peaking Safety and navigation related

changes caused by sudden rise

or drop of water levels

Pulses by operations idem

jan dec

flow

jan dec

flow

Secondary (indirect) risks through impacts on sediment

movement, fish, navigation, water quality

primary risks

that have

been

identified for

the

mainstream

dams

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Example: annual/seasonal impacts of storage schemes

Lower reaches of the Mekong River will: • have higher flow in dry season • have later start of wet season • have lower high flows in start of wet season

UMB (main)

LMB (main)

3S

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Example: annual/seasonal impacts of storage scheme in the Colorado River USA

Glen Canyon dam Lake Powel 1296 MW

Dis

char

ge

Year

1963

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Example: Cumulative impacts of small hydropower North Vietnam

Nam Chien 2

Pa Chien

PS

PS

PS

Nam Chien 1 Limited

sediment

entrapment

Large reservoir

blocks much

sediment and

discharge

Q

t

Bypass: river

only wet

during flood

Q

t

Q

low ‘high flow’,

high ‘low flow’

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Example: impacts daily fluctuations of HP operation: Colorado River USA

range of water-level variation

46

15 January 2018

Water level Mile 87

=0.6 m

Daily fluctuation related to power peaking: • Causes erosion of sand bars

(bank erosion)

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Step 3: Quantification: Indicators and monitoring

System

components LMB level National/ local level

Hydrology

And Flow

Flow (sub-daily/ every hour or

minute)

Water level (sub-daily/ every hour

or minute)

Onset of wet season

Duration of wet season

Minimum flows

average wet season peak daily flow

average flow volume entering Tonle

Sap

monthly average dry season flow

(i.e. flow in march)

total wet season flow volume

Table 2.2. Hydrology and Flows indicators.

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0-D Catchment & basin models

Detailed 3D reservoir models (cascade), ½-D hydropower models

Downstream impacts: 1D hydraulic models

Step 3: Quantification: use of modelling tools

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Step3: Testing impacts: compliance with PMFM1 flow procedures (example)

Dry season planning purpose flow criteria (Vientiane)

Wet season planning purpose flow criteria (Vientiane).

90% FDC

1 Procedures for the Maintenance of Flows on the Mainstream

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multiconsult.no Step 3: Testing impacts: compliance with PMFM flow procedures: result for upper cascade

Scenario calculations with PMFM flow criteria (dry season at Vientiane) – 90% values (monthly values).

90% FDC (criteria)

90% historical

BDP2030 & mainstream dams

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Step 3: Compliance with PMFM flow procedures: result for upper cascade

90% historical

BDP2030 & mainstream dams

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Step 3: Upper cascade: seasonal changes

Wet season

onset

Wet season

duration

historic

14 Jun

±36 days

152 days

± 36 days

BDP

2030

26 Jun

±39 days

142 days

± 37 days

Sc. 1.1.0

25 Jun

±39 days

142 days

± 37 days

Conclusions: the wet-season flow volume and the daily characteristics do not differ between the cascade-scenarios; major difference between historic and BDP2030 future (Chinese dams and tributary dams)

UPSTREAM LUANG PRABANG

Indicator: Flow volume of the wet season Indicator: daily flow characteristics

Violin plots

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Step 4: Identify mitigation options appropriate to values and risks

• Wide range of mitigation options:

- Designing HPPs that minimise impacts & maximise mitigation options

- Implementing infrastructure to enable mitigation

- Developing operating rules to achieve mitigation goals

- Coordinating operations with other HPPs minimise impacts and maximise mitigation

- Implementing catchment management to reduce overall impacts and maximise benefits

• Mitigation approaches may change over life-cycle of project

- Construction / operations / decommissioning

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Step 4: Avoidance – Mitigation - Compensation

• The risks, impact and vulnerabilities is the basis for the detailed mitigation options

• Using the full mitigation hierarchy (avoidance, minimization, compensation) should be the New Frontier for the LMB countries

http://www.raymondsumouniversity.com

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Step 4: Identify mitigation options

• Use of the Tables in Volume 1 and find details on solutions in the Manual

Distinguish: • planning/design

(mostly new dams) • Operation (mostly

existing dams) • Consider the

mitigation hierarchy

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Risks / Impacts

Table 5.1 (I) Annual/Inter Annual Changes to Flow

Planning / design / construction

MP=Master Plan; F=Feasibility Stage; D=Design; C=Construction

Operation

Options Indicators Options Indicators

Hydrology and downstream flows

1) Change of timing & duration of

floods and low flows

2) Peaks in flood and low flow change,

smoother hydrograph

3) Changes in Tonle Sap flows and salt

intrusion in the delta

Geomorphology and Sediments

1) Water logging & loss of vegetation leading to increased bank erosion

Increased erosion due to increased

scour

2) Winnowing of smaller sediment

leading to bed armouring & reduction

in downstream sediment supply

3) Channel narrowing through encroachment of vegetation 4) Decoupling of tributary & mainstream flows. Erosion and / or deposition due to tributary rejuvenation 5) Backwater sedimentation causing flood-level increase upstream

Water quality

1) Changes / loss of seasonal

temperature patterns downstream

2) Increased water clarity increasing water temperature and risk of algal growth

Fisheries and Aquatic Ecology

1) Loss of migration/ spawning

triggers;

2) Reduced flood pulse and related

productivity loss;

3) Habitat loss due to morphological

alterations

Biodiversity, Natural Resources and

Ecosystem Services

1) Changes in wetland functions and

dynamics due to shifts in timing of

sediment and nutrient delivery

2) Loss of wetland/floodplain habitats

(I.1) Avoidance

(I.1.1) Dam siting in Master Plans

to avoid risks and impacts in

themes hotspot areas

(I.1.2) Selection of sites with less

hydrological and sediment impact

River length affected;

contribution to LMB flow and

sediment loads

(I.2.) Mitigation

(I.2.1) Development of flow

rules (MP and F)

(I.2.2) Develop joint operation

rules for releases (F)

(I.2.3) Design multiple large gated

spillways/outlets at multiple levels,

and low level sediment outlets (D)

(I.2.4) Design bypass channels (F

and D)

Minimum flow, hydraulic

parameters, magnitude,

duration, timing of wet and

dry season flows

(I.2.5) Mimic ‘natural’

flow regime (artificial

releases, environmental

flows)

(I.2.6) Maintain seasonal

patterns through HP

operations

(I.2.7) Annual sediment

sluicing to maintain

seasonal pulse

(I.2.8) Monitoring of

impacts

Minimum flow; onset

of wet season;

magnitude, duration

of wet/ dry season

flows (flow duration

curve); changes to fish

diversity/ biomass,

sediment loads and

timing of sediment

delivery, extent and

timing of salinity

intrusion

(I.3) Compensation

Plan for and implement;

(I.3.1) Creation of offsets of

residual impacted habitats and

areas (F and D)

(I.3.2) Floodplain and wetland

rehabilitation (F and D)

Area of offsets and improved

floodplain and wetland

habitats

(I.3.3) Monitor offsets

and floodplain and

wetland rehabilitation

Changes to diversity/

biomass of fish and

other aquatic

organisms

(I.4) Adaptation

Implementation of operating rules

Monitoring including stakeholder consultation to gauge effectiveness of mitigation actions

Adaptive management guided by monitoring

Catchment management activities to improve / maintain water quality, reduce sediment loads

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Risks / Impacts

Table 5.2 (II) Short-term flow fluctuations / Hydro-peaking

Planning / design / construction

MP=Master Plan; F=Feasibility Stage; D=Design; C=Construction

Operation

Options Indicators Options Indicators

Hydrology and downstream flows

1) Short term flow fluctuations

2) Safety and navigability

Geomorphology and Sediments

1) Rapid wetting and drying of banks

2) Increase in shear stress on river

channel

Water quality

1) Fluctuating temperature and water

quality

2) Altered concentrations of

downstream WQ parameters

Fisheries and Aquatic Ecology

1) Degradation of riparian and instream

habitats

2) Thermopeaking

3) Increased fish/ macroinvertebrate

drift and stranding

4) Offset of migration triggers

5) Loss of food sources

Biodiversity, Natural Resources and

Ecosystem Services

1) Degradation of function, dynamics

and ecosystem services of wetland and

riparian habitats

(II.1) Avoidance

(II.1.1) Dam siting in Master Plans to

avoid risks and impacts in themes

hotspot areas (MP)

(II.1.2) Selection of sites where impacts

are reduced by entering tributaries (MP)

River length affected;

quickly dewatered

area

(II.2.) Mitigation

(II.2.1) Development of flow rules

(F and D)

(II.2.2) Design of re-regulation weir (D)

(II.2.3) Coordination of multiple

hydropeaking HPP

(II.2.4) Design of aeration weir (D)

(II.2.5) Avoidance of flow fluctuations

during construction (C)

(II.2.6) Establish protected areas and

evacuation paths for inundation zones

(C)

(II.2.7) Flexible mooring structures for

ports (D and C)

(II.2.8) River-bank stabilisation works (C)

Ramping frequency,

amplitude, ramping

rate, minimum flow

temperature,

dissolved oxygen,

downstream damping

of water-level

fluctuations

(II.2.9) Re-regulation

warning systems

(II.2.10) Operating rules to

minimise flow changes,

management of re-

regulation weir to provide

appropriate downstream

flow

(II.2.11) Monitoring of

impacts

Ramping frequency,

ramping amplitude,

ramping rate, minimum

flow, changes to fish

diversity/ biomass. Bank

/ bed erosion rates

Downstream

temperature, D.O.

downstream damping

of water-level

fluctuations

(II.3) Compensation

Plan for and implement;

(II.3.1) Habitat improvement (F & D)

(II.3.2) Floodplain and wetland

rehabilitation (D and C)

Area of improved

floodplain and wetland

habitats

(II.3.3) Monitor habitat

improvement and

rehabilitation

Changes to fish

diversity/ biomass

(II.4) Adaptation

Monitoring, adaptive management (based on monitoring data)

Catchment management to maximise water quality in and discharged from impoundment

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Mitigation measures (examples)

Ramping (limit water level change)

Artificial flood Diversion channel

Flow regulator

Mitigation examples

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Example: mitigation seasonal impacts Tonle Sap

• Impacts to be mitigated:

• Mitigation: - Increase profile of Tonle Sap River - Create upstream diversion channel - Generate flood pulse (600-700 Million m3)

Not a solution for the delta (Tonle Sap en flood plains act as storage and will absorb the pulse!

Blue: increase

Green: decrease

Tonle

Sap

Mekong

Flood

plains

Timing of flow reversal Change in volumes exchanged

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Example: daily fluctuations (power peaking)

• Ramping (rate in m/hours at which water levels may change):

- Relevant for ecology (fish stranding), navigation, safety, etc.

- Consider natural rates of water-level variation (for instance 0.05 m/hour)

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Example: Regulation weir at Nam Ngiep 1

• The re-regulation reservoir is to store water discharged from the main dam for 16-hour peak power generation, re-use it for power generation and release it downstream evenly on a 24-hour basis on weekdays and Saturday

• Operation level between EL 174.0 and EL 179.0 (eff. Storage 4.6Mm3)

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Example: backwater upstream of Pak Beng reservoir

Pak Beng dam: transboundary issue. Impact: During dry season Keng Pha Day reefs should be emerged. Due to backwater of dam the reefs get submerged.

Mitigation: Model results show that water level can be reduced at low discharge by applying a 5 m lower operation level during dry season

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Step 5: Take home messages

• Mitigation for flow covers the full life cycle of the reservoir (many generations) and a full basin (including other developments in the Mekong basin)

• The large extent of the flow impacts of any scheme means that trans-boundary issues are relevant

• The ISH0306 guideline does not cover all aspects (socio-economics, dam-safety, navigation), but that does not mean these have no consequences for mitigation of HP impacts

• Mitigation of annual/seasonal impacts often involves joint operation of multiple dams

Hydrological mitigation is mostly for impacts which are not directly hydrological, but more aimed for indirect effects, for instance for fish and sediments

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Summary of approach for hydrology and flow mitigation in ISH0306

• Review literature, regional experience, international experience - ISH Manual contains many examples of mitigation approaches

relevant to the LMB - Aim of mitigation should be to retain values and minimise risks

through Avoidance, minimisation, mitigation Maximise operational flexibility

• Mitigation includes: - Planning – siting and design of projects - Infrastructure – gates, re-regulation weirs, aeration weirs, by-pass

channels - Operating regime - environmental flows (low, med & high

flows),ramping rates, lake level constraints, etc

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Questions?

Nam Ou, Muang Ngoi, Laos