Study On The Waterway Regulation Of Pebble Rapids Section Under Dam

The mountainous areas in the west of China were rich in hydropower resources.With continuous development and utilization of hydropower resources in recent years,more and more water conservancy hubs have been constructed.After the hubs were built and operated,not only could hydropower resources be obtained,but also deep-water channel be formed in the upper reaches,which improved the torrential and complicated navigation conditions of natural rivers.However,the construction of the water conservancy hubs would cause changes in the water-sediment conditions of the downstream reaches of the river,especially for the interception of sediments,which broke the original relative balance of the downstream river.In order to adapt to the new water-sediment conditions,the river would be adjusted by erosion and siltation,resulting in the change of river regime in the lower reaches,which would have a great impact on the navigation.With the change of water-sediment conditions,parts of the channel conditions in the original lower reaches of the dam were further deteriorated,and the problem of navigation obstruction was more prominent.When the tail water of upstream and downstream cascade hubs were not connected,the downstream reaches of the dam may become a bottleneck in shipping.The research was based on the channel regulation project in lower torrential reaches with pebble river bed of the Moshui Hub.In this paper,the multi-disciplinary theories such as river dynamics,river bed evolution sediment kinematics and channel rectification were applied,and relevant domestic and international research literatures were referred.The research on the channel regulation in lower torrential reaches with pebble river bed of the dam was conducted by adopting fixed-bed physics model tests,two-dimensional numerical simulations,ship model tests,moving bed physical model tests,and other related research methods.The main results are follows:(1)The principles of channel regulation in lower torrential reaches with pebble river bed of the dam were proposed: Firstly,the flowing cross-sections were enlarged to reduce the flow velocity.Secondly,we should make full use of the compound cross-section to adjust the velocity distribution and widen the width of the track zone with slow flow velocity to meet the navigation requirements.Finally,this program should take the effect of regulation and the comprehensive utilization into condition.(2)The regulation scheme for the lower torrential reaches with pebble river bed of the dam was set forth that dredging and trenching were integrated: Increasing the area of flow to decrease the flow velocity through the overall excavation of the lower torrential reaches with pebble river bed of the dam.The compound cross-section of the river bed was adopted to adjust the flow velocity distribution which made the overall velocity decreases,the main flow moved to the left and the peak flow velocity dropped in the lower reaches of the dam at all levels of the traffic flow.The navigation conditions have been fundamentally improved that the zone with slow flow velocity of the right bank was increased and the sweeping water near the corners was basically eliminated.(3)The asymmetrical compound cross-section played an important role in adjusting the flow velocity distribution during the channel regulation for lower torrential reaches with pebble river bed of the dam,and a zone with slow flow velocity was formed,which was conducive to the navigation of the ship and improve the navigable conditions of the lower torrential reaches with pebble river bed of the dam.(4)The improvement and effectiveness of the navigable conditions for regulation schemes were verified by ship model tests in this paper.The stability of the regulation schemes were verified through movable bed model tests.