Research On Principles For Channel Regulation Of The Jingjiang River Channel Improvement Under New Conditions Of Water And Sediment

The objective of the present study was to investigate the variation of the navigational conditions of the Jingjiang Reach in the middle reach of the Yangtze River after the impoundment of the Three Gorges Project and to carry out pointed engineering measures for the waterway improvement. Firstly, based on the analysis of the hydrological data before/after the impoundment, new characteristics of the water-sediment conditions of the research river reach were demonstrated. And then by applying a numerical model, the laws of the riverbed evolution were discussed and the evolution tendency was further predicted. In order to verify the adaptabilities of different kinds of regulation works to the operation of the reservoir, numerical simulations were conducted, in which the mechanisms of the protective engineering were thoroughly looked into, and as well the failure modes of the spur dikes due to multi-factors were also studied. Finally, a couple of regulation principles for the waterway improvement of the Jingjiang Reach were summarized upon the previous research results.Main contents of this thesis are as follows:(1) Hydrological data from different stations, e.g., Yichang, Zhicheng, Shashi, Jianli, Hankou were collected and analyzed, and it shows that after the operation of the Three Gorges Project the discharge hydrograph becomes flatter, the duration of the low flow period becomes shorter and the duration of the median flow period becomes longer. By the meantime, the water release from the reservoir is nearly sediment-free and the annual sediment transport volume at each station reduces sharply. Moreover, since the nearly-clear water picks up sediments as it flows, the degree of unsaturation of the water drops along the stream, thus it could be seen that the annual sediment transport volume gradually increases from upstream to downstream.(2) The laws of the riverbed evolution and the variation of the navigational condition in the research river reach were discussed under the new water-sediment condtions, and the correlation between the change of the water-sediment conditions and the fluvial process has been revealed. Upon that, different fluvial characteristics for different types of river reach, e.g., sandy-gravel reach, straight/meandering/bifurcated sandy-shoal reach, have also been uncovered.(3) Considering the correlation between the upstream and downstream, the evolution tendency of the shoals in the reaches of Zhijiang-Jiangkou, Zhoutian, Oushinian, Yaojian were predicted by using the numerical model. And upon that, the riverbed evolution tendency of different types of shoal reaches has been presented under new water-sediment conditions(4) For the navigation-obstructing river reach due to the impoundment of the Three Gorges Project, numerical simulations on the engineering adaptabilities of both protective regulation works and adjusting regulation works were performed. The results shows the protective works could be effective for the improvement of the waterway, however for certain river reach which is sensitive to the impounding process after flood period; the adjusting works is of necessary.(5) In application of the theories of river dynamics, an expression was established for calculating the variation of the navigational depth before and after regulation under the designed water level. And the mechanisms of the protective engineering were also discussed theoretically. In addition, numerical simulations of the Ouchikou Waterway and Taipingkou Reach within the Jingjiang Reach under the protective regulation works were also conducted. The results have shown strong evidence for the mechanisms revealed.(6) An unstructured-grid-based non-static pressure numerical model for 3-D free surface flow was established and was applied to detailedly simulate two common structures of spur dikes, i.e., the regular spur dike and the downstream-heading spur dikeunder different engineering conditions. The simulation results of the flow structure and pressure distribution feature shows that the front and the back end of a spur dike are the parts easiest to get destroyed. And moreover, the results also shows that comparing with the regular spur dike, the downstream-heading spur dike performs better in defending water failure.(7) Based on the results as previously stated, the thesis finally proposed a couple of regulation principles for the waterway improvement of the Jingjiang Reach were summarized, including the regulation principles using varied types regulation works specifically for the upper/lower Jingjiang Reach with different types of shoals.