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MRC Preliminary Design Guidance
 

MRC Preliminary Design Guidance

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By Voradeth Phonekeo, Mekong River Commission, Laos ...

By Voradeth Phonekeo, Mekong River Commission, Laos

Presented at the Mekong Forum on Water, Food and Energy
Phnom Penh, Cambodia
December 7-9, 2011
Session 2a: Water engineering

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  • Hydropower developments could pose a barrier to navigation, but they also offer the possibility of providing more reliable and consistent water depths that will facilitate larger vessel capacities.The MRC AGREEMENT, Article 9: promotes “Freedom of Navigation” where the content says“ On the basis of equality of right, freedom of navigation shall be accorded throughout the mainstream of the Mekong river without regard to the territorial boundaries, … ““ The Mekong river shall be kept free from obstructions, measures, conduct and actions that might directly or indirectly impair navigability, …We have to bear in mind the long-term nature of planning and investment for navigation locks. After dams, locks are the biggest and most expensive works on a navigable river. It is almost impossible to alter lock dimensions after construction, although building a second lock is possible. Lock dimensions must accommodate traffic increases in view of a 50 year planning horizon. The current situation in the Greater Mekong Region, is not a relevant frame of reference due to the rapid pace of development. Future uses of the river are expected to include transportation of heavy cargo such as mineral ores, containerised waterborne transportation and the introduction of inland cruise vessels.
  • 2. Determination of Optimal Ship Size When proposing the exact dimensions for ship locks, it is imperative to know what the longitudinal depth profile of the Mekong River will be after possible hydropower dam development. Information required from the Optimisation Study of the Mekong Mainstream Hydropower Projects:The minimum and maximum water levels that can be maintained in the back water of the dams. The extent of the free-flowing stretches of each hydropower dam.The water level and the conditions of the navigation fairway that can be maintained in the free flowing stretches. 3. MRC Recommendations for Standard Specifications for Ship Locks on Mekong Mainstream DamsPhase 1 includes a Review of International Ship Lock Dimensions and their Relevance to the Proposed Hydropower Developments on the Mekong Mainstream (completed)Phase 2, Standard Specifications for Construction and Operation of Navigation Locks (to be started upon completion of the Optimisation Study)However, until the results of the Optimisation Study are fully known, minimum requirements should not be lower than the planned design of the Gan Lan Ba Dam in China:Furthermore, a parallel slot is reserved for a second lock to double the capacity during a future expansion.ly way to efficiently realise the benefits of inland waterway navigation in harmony with hydropower development is the construction of navigation locks
  • Dams interrupt the natural continuity of sediment transport in river systems, inducing deposition within the reservoir and releasing sediment‐starved water downstream, which typically produce channel adjustments and potentially reduce the tailwater. Deposition of sediment in reservoirs will shorten the reservoir’s economic life and can interfere with reservoir functions, as well as increase pressure on the dam and increase backwater effects. Changes in either river flow or sediment load can also induce changes in the form and dimensions of alluvial channels downstream. Localized sediment deposition may also affect critical mechanical equipment at the dam, such as reservoir flood gates and turbine intakes. Sediment that builds up in the wrong location can compromise the safe working of the dam, its ability to pass the design flood without overtopping and the longevity of the turbines.
  • On the Mekong River system, sediment starvation can be expected to result in loss of large bedforms and gravel/sand bars, and ultimately increased bank erosion in alluvial reaches, reducing channel complexity and affecting habitats formed of loose alluvium. Changes in sediment delivery may affect the Tonle Sap and exacerbate existing problems of coastal erosion in the Mekong Delta caused by sand extraction from the river channel.
  • Water quality and biodiversityDesign recommendationsPerformance targetsWater quality criteria or standardsTemperatureEnvironmental flows Design and operating principles for mitigationWhat can be done to fulfil the targetsCompliance monitoring and adaptive managementMonitoring performanceMonitoring and optimisationWater quality goal for the MekongMRC Procedures for Water Quality - To maintain good/acceptable WQ in the Mekong River BasinPerformance target for the impoundments:Criteria and standards for human health and aquatic life and framework for water quality emergencyMonitoring: MRC Water Quality Monitoring Network Specific monitoring inside and downstream the impoundmentProposal for guidance:Criteria from the Technical Guidelines of Procedures for Water Quality with amendment related to deep impoundments Water quality issuesDissolved oxygen- Low oxygen concentrations due to anoxic conditions at the bottom of deep impoundmentsTemperature alterationsCold water from the bottom of impoundmentsAmmonia and sulphide release- Chemical reduction due to anoxic conditions at the bottom of impoundmentsDetermining factorsPhysical dimensionsUpstream water sourceOperationBiodiversity issuesPotential ecosystem and biodiversity impacts- dependence on natural hydrological variability- ecological balance, - habitat fragmentation Performance targets:Environmental flows maintaining minimum flows Temperature within natural variabilityWater quality managementMinimisationOf stagnation/stratification of the impoundment.Optimisation of water quality and temperatureCriteria in the Technical Guidelines of Procedures for Water QualityHigh levels of dissolved oxygenLow levels of phosphorus, nitrogen, BOD, bacteria causing diseasesMinimising temperature deviations from natural conditions.Minimum flow requirements and restrictions on changes to natural variability.Questions for discussionHow important will this aspect be?Care should be taken not to ignore it just because the WQ is very good now and care should be taken not to blow it out of dimensionsHow to approach this?Proposal for a study to document the existing situation in impoundments in the LMB, national and international experiences outside the basin and suggest best practices
  • To identify Safety issues associated with characteristics of the proposed low-head damsMechanical and electrical control equipment very thoroughly backed up/doubled up, to ensure capability in emergencies. Comprehensive dam safety reviews need to be scheduled at least once every five years. Use of Relevant national standards and application of government framework for the safety Adopting international best practice(i) a construction supervision plan (ii) a quality assurance plan (iii) an instrument plan (iv) an operation and maintenance (O&M) plan, and(v) an emergency preparedness plan (EPP).

MRC Preliminary Design Guidance MRC Preliminary Design Guidance Presentation Transcript

  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia MRC Preliminary Design Guidance MRC Initiative on Sustainable Hydropower Dec 2011 1
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Meetings to disseminate the content of the 2 MRC Preliminary Design Guidance
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia 3
  • Design guidance documentBased on 5 basic principles• Avoidance of impacts where possible• Precautionary principle (esp avoid biodiversity loss)• User pays• Adaptive management• International good practice
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Guidance for navigation lock design and operations MRC AGREEMENT Article 9: Freedom of Navigation “ The Mekong river shall be kept free from obstructions, measures, conduct and actions that might directly or indirectly impair navigability, … 5
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Preliminary Recommendations for Lock Dimensions on the Mekong River Length 130m Width 12m Depth 4m Future doubling of the locks if traffic increases in parallel set- up to a width of 24m. These specifications are based on international standards, recommendations by the International Inland Navigation Association (PIANC), and assessments of Chinese waterway classifications in the case of rivers associated with hydropower developments 6
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , CambodiaFish migration in the Mekong Approximately 50% of total fish catch in the lower Mekong basin is dependent on long distance migration – white fishes (about 1 million tonnes worth >US$1,500-2,000 million) Important for rural livelihoods Biodiversity – 2nd to Amazon
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Guidance for Fish passage Fish movement at Khone Falls from Baran 2006 – Fish migration triggers in the LMB and other tropical freshwater systems
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Dams impact on river fisheries Barrier to fish migration – upstream and downstream| Result is fish cannot complete their life cycle Spawning reduced or stopped Population size reduced Declining fisheries yield Impact on people
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Solution = Build a fish pass ?? Three requirements for successful fish passes 1. Fish must find entrance 2. Fish must be able to ascend / descend 3. Fish must exit and continue migration
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Mitigation – fish ladder – low dams only (<6-10 m)
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Mitigation – fish lock – low-medium dams (<10 m dams)
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Mitigation – fish lift or elevator – potentially high dams
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Design guidance document 52. Fish passage must be incorporated – upstream and downstream 53. Safe passage for 95% target species, all flow conditions 57. Adopt best international practice, utilise core expert group, developer pays 63. Mortality through fishways < 5% 65. 10% of low season flows through fish pass 84. Contingency fund for modification – 20% of initial cost of fishway
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Sediment management and River Morphology As dams trap sediment. They release waters with reduced sediment loads, called sediment‐starved or “hungry” water. These flows downstream of the dam possess more energy to transport sediment, but may have little or no sediment. The excess energy of these flows can typically cause erosion of the channel bed and banks. If coarse materials are not present in the bed, bed incision cannot be stopped and can reach significant depths of many meters. 15
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Environmentally friendly flushing Send downstream only the concentration of sediment that the environment can withstand 600m3/s Weak concentration C = 1g/l Half depth gate C1 Q1 Bottom gate Concentration20 g/l g/l C = 20 C2 Q2 peaks up to 80 g/l gate discharge regulation REAL TIME Concentration 5g/l Concentration measurement Francis Fruchart, CNR France 16
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Need for a coordinating body for dam operation Major roles  Optimise operation of dam cascade for electricity generation  Manage flood risk  Coordinate and optimise sediment flushing activities  Coordinate environmental monitoring Feedback to dam operation 17
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Cumulative impacts in sensitive areas Alluvial reach  Alluvial reaches are most sensitive to morphological change because they have highly erodable bed and banks Alluvial reach Planned mainstream dam 18
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Water Quality and Aquatic Ecology In general satisfactory based on WQ monitoring Ecological Health Monitoring 19
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia MRC Procedures for Water Quality -To maintain good/acceptable WQ in the Mekong River BasinPerformance target for the impoundments: • Criteria and standards for human health and aquatic life and framework for water quality emergencyMonitoring: • MRC Water Quality Monitoring Network • Specific monitoring inside and downstream the impoundmentProposal for guidance: • Criteria from the Technical Guidelines of Procedures for Water Quality with amendment related to deep impoundments
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia Guidance for Safety of Dams  The safe design, construction and operation of dams depends on more than engineering factors.  Dam safety is a complex process.  National requirements and international good practice for the safety of dams.
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia • Safety issues associated with characteristics of the dam • Mechanical and electrical control equipment backed up/doubled up, to ensure capability in emergencies. • Comprehensive dam safety reviews • Relevant national standards and government framework for the safety 22
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia World Bank Operational Policy on Safety of Dams  Experienced and competent professionals design and supervise construction.  Dam Safety Panel  An instrument plan  O&M procedures and arrangements  A clear communication strategy to engage with stakeholders on dam safety issues and emergency preparedness activities 23
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia  In particular, developers / owners / operators should – prepare and implement a Dam Safety Management System (DSMS) – be responsible to check for periodic updates of the World Bank Operational Policy – be responsible for all cost associated with implementing all aspects of this guidance on the safety of dams – clearly detail all such costs in the project budgets for the design, implementation and operation stages 24
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia 25
  • Mekong Forum on Water, Food and Energy7-9 Dec 2011, Phnom Penh , Cambodia “The major problems in the world are the result of differences between the way nature works and the way people think.” Gregory Bateson 26