Preliminary Design Guidance for Proposed Mainstream Dams in the Lower Mekong River Basin

296. The objectives for navigation are:

• Guarantee continuation of navigation on the Mekong mainstream consistent with Article 9 of the Mekong Agreement, through provision and management of ship locks at all mainstream dams.
• Ensure consistent design and operation of ship locks at all mainstream dams.
• Make sure that dam infrastructure does not impede the potential future development of mainstream navigation16 in terms of cargo transport capacity, passengers transport capacity, and convoy transport development.
• Ensure safe and efficient lock operations.

297. Risks associated with navigation should be comprehensively assessed. The PNPCA documentation should indicate how the design has dealt with the potential risks associated with navigation, and in particular with the ship lock, as shown in Table 8.1.

298. Design of navigation facilities should take account of the design and operation of existing and planned upstream and downstream projects in a cascade.

299. The design should be informed by current and future proposals for free-flow channel improvements both upstream and downstream of the dam. A number of projects, studies, and proposals are under consideration, the most important being the Development Plan on International Navigation on the Lancang-Mekong River (2014–2025) by the Department of Transport of the Yunnan Province, August 2014.

300. The design should take into consideration two studies conducted by the MRCS regarding channel improvements in some dangerous areas for navigation (including reefs, rapids, and shoals):

• “Condition Survey of Dangerous Areas for Navigation between Luang Prabang and Pakse in the Lao PDR and Thailand – October 2009”; and
• “Condition Survey of Dangerous Areas for Navigation between Huay Xay and Luang Prabang in the Lao PDR and Thailand – April 2010”.

301. The developer should base the lock design on a detailed understanding of the geological, geomorphologic, hydrologic, and hydraulic conditions of the dam site, including seasonal variations. Application of the hydrological and hydraulic models described in Section 2.3 and the sediment modelling described in Section 3.3, can inform detailed planning for development and operation of the ship locks and its approaches.

302. Adequate channel clearance should be provided for vessels accessing the ship lock. The need for dredging or rock clearance to ensure safe access to the lock chamber should be documented. Adequate visibility of both upstream and downstream lock accesses should be provided.

303. The analyses of changes, risks, and mitigation options relating to navigation should clearly identify the residual impacts and document where these will occur in the river, in line with Clauses 7 and 25.

304. An essential guide for many of the design aspects for the mainstream Mekong ship locks is the 2009 Permanent International Association of Navigation Congresses (PIANC 17 report). Innovations in Navigation Lock Design; and an essential guide for Mekong navigation is the PIANC InCom WG report n⁰ 141-2019, Design Guidelines for Inland Waterway Dimensions. It is the developer’s responsibility to obtain these guidance documents through the PIANC procedures. This Preliminary Design Guidance (PDG) directs the user to specific sections of these PIANC reference documents for important design requirements.

305. Mitigation options should be evaluated to determine which ones will best address identified risks. Table 8.2 sets out mitigation options for the broad areas of risk, with more detailed guidance provided in the clauses following this table. Developers may propose alternative mitigation options based on the specific site location and associated risks with appropriate justification.

Lock dimensions

306. Lock dimensions have been decided for all navigation locks to be constructed along mainstream dams, following the outcome of the Optimisation Study of the Mekong Mainstream Hydropower Projects commissioned by the Government of Lao PDR. Ship 18 PIANC-InCom report from working group 29 (Report n⁰ 106-2009): “Innovations in navigation lock design”, Section 4.4.5 (p. 82). lock chamber dimensions should be at least 120 m x 12 m x 4 m, which comfortably accommodates a convoy of two 500-t barges (Chinese design) with pusher vessel.

307. The Mekong/Lancang River upstream of the Khone Falls should be considered as a single navigation unit using the above ship and lock dimensions. Downstream of the Khone Falls (Cambodia – Viet Nam), different ship lock dimensions may be applied since this is another separate navigation unit with potential connection to the sea. Lockage time and availability

308. Lockage time should be kept to the minimum whilst allowing for safe operations and safe movement of all vessels in the lock chamber(s) and should be guided by PIANC recommendations.19

309. The design criterion for hawser forces in all possible directions should be ≤ 1% x water displacement of the vessel (in tonnes) and should be guided by PIANC recommendations.20

310. The locks should be designed to operate at least 12 hours a day, every day of the year.

311. Each lock complex should be operational for at least 98% of its scheduled operating time during each year of its service life, excluding planned closures for scheduled maintenance and unscheduled repairs.

312. Outages related to incidental breakdowns should not exceed 2 percent of the operating time each year.

313. Service outages for scheduled maintenance should be on nine consecutive days (one working week and the two weekends) each year, during the same period for all dams on the Mekong mainstream waterway (upstream of Khone Falls) to avoid traffic disruption. This period should be established in the Cascade Joint Operating Rules. The official body in charge of navigation coordination along the Mekong River should be responsible for specifying the dates for servicing.

Approach infrastructure

314. Approach infrastructure should be designed in accordance with PIANC recommendations.21 Three different berthing areas should be provided, each able to berth one full-sized design vessel/convoy, and include the following:

• a lay-by area where ships can be ready to immediately enter the ship lock as soon as the preceding vessel has left it or the green entry light is turned on;
• a waiting area where ships can wait if there are several others ahead of them. The 19 See PIANC (2009), Chapter 4.2.5 Duration of Lock Cycle and Vessel Passage (p. 56). 20 See PIANC (2009), Chapter 5.2.3 Mooring Line/Hawser Forces during Filling and Emptying of Lock Chamber (p. 109). 21 See PIANC (2009), Chapter 5.6 Lock Approach Structures (p. 148). waiting area can be an extension of the lay-by area;
• the overnight area where ships and vessels can spend the night. The overnight area does not necessarily have to be connected to the lay-by or waiting areas, but all three areas should have access to land via a catwalk or via floating pontoons. The overnight area may be developed at a later date if demand is low at the time of project commissioning, and plans submitted at the PNPCA stage should indicate if this is the case and how it has been provided for; and
• one of the above three areas may provide facilities such as potable water, clean water, solid and liquid waste facilities, emergency aid, etc.

Service life

315. Each lock complex should be designed for a functional lifetime of 100 years.

316. Some components of the lock may have a service life shorter than 50 years. These components are listed below and should be designed to allow for easy replacement.

• Metal structures
• Hydraulic jacks
• Ball bearings, pulleys, joints, valves, etc.
• Cables
• Electrical equipment
• Communication and digital safety equipment, cameras, and TV sets.

317. Sufficient spare parts should be obtained during project implementation for the most vital mechanical parts of the ship lock. Guidance on life cycle management for locks is provided in the PIANC reference.22

Future expansion

318. The design of the locks system should allow for future construction of a second line of locks.

319. The owner/operator should be responsible for the construction of a second line of parallel locks when the number of lockages per year reaches at least 80 percent of the total maximum possible yearly lockages over a period of two successive years. 22 See PIANC (2009), Chapter 4.3 Life Cycle Management for Locks (pp. 58–63). Further design and operational guidance

320. Lock gates and their ancillary equipment should be protected against fire inside the chamber.

321. An overhead rolling crane, or other lifting equipment, running the full length of each chamber may be considered to:

• lift floating or sunken debris caught between the mitre door and the sill or lodged inside the door chamber;
• assist small vessels in cases of emergencies inside the lock chamber;
• position the stoplogs for each lock-head for maintenance purposes (e.g. mitre door pintle replacement) and repair/replacement of the tainter or sliding valves in the culverts; and
• support emergency rescue operations for ships in distress inside the lock chamber.

322. If feasible, the ship lock may also be used as additional fish passage during migration periods (see Clause 231). This additional fish passage may be the only one during the construction of the powerhouse and the spillway, in which case it is an essential asset to be considered in the construction planning and should be operated as a fish passage during construction.

323. The project should make allowance for the installation of a monitoring system that allows future networking to other mainstream dams, to provide a real-time monitoring of vessel and barge movements on the Mekong. This may be the precursor of a fully-fledged River Information System, in which the real-time movement of vessels and barges is monitored and communicated to upstream or downstream locks and ports.

324. Plans for project monitoring of navigation locks should take into account the guidance in Clause 26. The PNPCA information should demonstrate that plans for navigation-related monitoring information to be collected during construction and operation will inform:

• Developers’ needs regarding management of navigation lock operations; and
• Indicators that may signal a need for adaptive management responses to navigation related management and mitigation measures.

325. The monitoring programme for navigation at the construction and operation stage should include a focus on operational efficiency, adherence to the minimum lock downtimes, effectiveness of communications and coordination, and maintenance and replacement of operating components.

326. Plans for the monitoring programme should include regular monitoring and inspections by the navigation lock operator of key navigation infrastructure, electro-mechanical equipment and keep records of navigation movements and any associated issues arising. Bathymetric surveys at both access channels and approaches should be conducted in coordination with related sediment monitoring set out in Section 3.5.