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transcript
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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
multiconsult.no Step 2: risks, impacts, vulnerabilities of HP development
• 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