PIANC Smart Rivers 2022

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Abstract: The navigation flow condition of the entrance area and the connecting section of the approach channel is an important factor affecting the safe navigation of ships, which is jointly affected by multiple factors such as terrain, layout, and operation scheduling. At the same time, for the project with large number of generator units and discharge sluices, the impact of operation scheduling mode on the navigation water flow conditions of the ship lock is also prominent. Pak Beng Hydropower Station is the 1st cascade of the 11 cascades in the development scheme of Mekong River, located in the upper reaches of Mekong River and Pak Beng of Oudomxay Province in northern Laos. The project is composed of non-overflow dams on both banks, floods-discharging and sand-sluicing gates, power station buildings, ship locks and fishways. The crest length is 899.5m and the maximum dam height is 69m.The powerhouse dam section is located in the left main river channel with18 generator units; the flood discharge and sand sluice dam section is located in the right bank beach, arranged 14 discharging sluices with the size of 15m×23m; The ship lock dam section arranged on the right bank is designed according to the standard of 500t navigation ship, and the effective size of the lock chamber is 120m×12m×4m (length× width× threshold depth). As Pak Beng Hydropower Station is characterized by curved river section, large number of units and sluices, and large total discharge, the contradictions between flood discharge, power generation and shipping are very prominent. To this end, the hydraulic model with a scale1:100 is used to carry out a comprehensive study on the flood discharge, sediment trapping and discharge, and navigation flow conditions. The upstream navigation flow conditions of the upstream approach channel with floating navigation embankment and the pier-plate navigation embankment, and the downstream navigation flow conditions of the downstream approach channel with permeable section were tested. The structural types of the upstream and downstream navigation buildings are optimized, and the maximum navigable flow is determined. In addition, an optimal scheduling scheme is proposed considering energy dissipation and anti-scouring comprehensively. The results show that the navigable guarantee rate can reach more than 95% under the flow rate of 10000 m3/s, so 10000 m3/s is determined as the maximum navigable flow. Under the maximum navigable flow, the upstream navigation wall adopts the floating navigation dike, the downstream adopts the navigation wall and additional permeable piers, and the number of units must reach more than half of the dispatching mode, which can not only meet the upstream and downstream navigation water flow conditions, but also make the outflow velocity of the stilling basin not greater than the anti-scour flow velocity of the riverbed.

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