Research On Remediation Measures Of Steep-slope Rapid In Lancang River

Torrent rapids account for 80% of the various beaches in the Lancang River and are the most important obstruction to navigation in the Lancang River.In the process of management of Lancang River beaches,it is found that there is a type of fast flowing beaches between the narrow channel type and the cross-stem type-steep slope type fast flowing beaches.Therefore,it is necessary to find a reasonable and effective remediation measure for steep-slope torrent rapids.In this thesis,the physical model test and mathematical model test are used to study the reasonable remediation method of steepslope torrent rapids to provide scientific basis for the remediation of this type of beach.The main contents and results are as follows:(1)Through the analysis of the actual measurement data and model test results of typical steep-slope fast-flowing beaches such as the Matai estuary beach,He Kuan Shang beach and San Dao Kuan beach of Lancang River,a new type of steep-slope fast-flowing beaches was proposed,and the characteristics and causes of obstruction to navigation of these beaches were summarized.Most of the steep-slope torrent rapids in Lancang River are bedrock riverbeds,and the riverbeds are raised longitudinally while the snag section is contracted laterally.The length to width ratio of steep-slope torrent rapids is 8～10,while that of the torrent rapids is about 0.3.Compared with the general cross-ridge torrent rapids,steep-slope torrent rapids have relatively long long longitudinal projections,large average valley drop,deep pools under the torrent rapids,and curved planform,with steep slopes and bad flow patterns such as plunge,surge,sweeping water,scissor water and backflow.Vessel navigation,channel improvement is more difficult.(2)A generalized model of steep-slope torrent rapids in Lancang River was established based on the model of He Kuan Shangtan,and the effects of two types of remediation measures were compared and analyzed through a two-dimensional mathematical model of water flow,namely,excavation of the general lateral slope of the steep-slope torrentrapids to expand the drainage area and dredging of the river bottom to expand the drainage area and adjust the longitudinal slope of the channel.From the comparison results of engineering excavation volume,water surface line and ratio drop change and flow velocity distribution,it is found that the remediation method of dredging to adjust the ratio drop of dry water main channel is more suitable for steep-slope type fast flowing beaches.(3)Based on the grade IV channel training project of Matai River mouth beach at the end of Nuozadu reservoir of Lancang River,the training measure of dredging the river bottom to expand the water discharge area while adjusting the longitudinal slope of the channel was applied to the training of this beach,and the training plan of this beach was optimized.The multi-plan optimization test shows that the remediation effect of Plan 4 is relatively good by adopting the appropriate longitudinal slope of clearing and dredging to increase the scale of the channel and expand the drainage area as the "upward spreading" measure,and the "downward lifting" measure of filling the channel with a deep trench under the beach.The test results show that the steep slope remediation measures proposed in this paper are feasible.