Research On Remediation Technology Of Hekuantan Rapids Group In Lancang River

According to the requirements of the“Lancang-Mekong River International Shipping Development Plan(2015-2025)”,the channel grade of the 244 Jiebei to Lincang Port will be raised from Grade V to Grade IV.For the small and medium-sized rivers in the mountainous areas such as Hekuantan,increasing the channel scale request to increase width and depth of the channel.The expansion of the trough will cause the water level of the complex beach group to fall and the flow conditions to deteriorate.Therefore,it is a key issue to solve the contradiction between the increase of channel scale and flow conditions.This thesis mainly uses the combination of physical model and mathematical model to study the remediation technology of Hekuantan.The main contents and results are as follows:(1)Analysis and summary of the characteristics and causes of the obstacles in the Hekuantan:Hekuan Shangtan is a rapid-flowing shoal obstructing navigation all year round.Hekuan Zhongshangtan is a spur-type and mid-flood shoal,the navigation width of the convex mouth is insufficient and the water flow is disordered.The 6-7clearing area of Hekuan Zhongxiatan is misplaced flooding shoals and the 8-10clearing area is a narrow trough type of flooding shoal.The greater the flow is,the more sturdy the rapid is.The 11 clearing district of Hekuan Xiatan is a perennial horizontal ridge rapids.The smaller the water flow is or the greater the flood flow is,the more turbulent the rapids will be.(2)The mutual influence of the remediation measures of the rapids group is relatively large.The preliminary design conducted excavation measures for the entire rapids group.When Q?1635m~3/s in the design scheme,there is a significant decrease in the upwelling resistance of Hekuan Xiatan,but it causes a significant water level drop in the upstream.When Q=840m~3/s,the water level drop value at the exit of Zhongxiatan was 0.85m,and the water level drop of Hekuan Shangtan is 0.2~0.47m,resulting in the deterioration of the situation of Hekuan Shangtan and Zhongshangtan.It can be seen that the measures of the each rapid in the rapids group are mutually influential,and the water level must be controlled during the remediation.(3)Control and optimization of key rapids:(1)Hekuan Shangtan is a complex rapids shoal.Different trenching types and drowning measures are adopted to minimize the water level drop.At the same time,based on the wide and shallow trenches on Hekuan Shangtan,the digital model is used to discuss the way of trenching on the most tumultuous flow rate of 1000m~3/s.(2)For#3 area,which is the mouth-shaped rapid,the width of middle dry water is insufficient.In view of the fact that this rapid section only meets the requirements of a single line and does not have the conditions of meeting ships,it is recommended to adopt the width of a single-line for this channel.(3)For#9-10,the narrow groove type of middle flood rapids,the excavation cross section can be arranged as a complex section with small dry water excavation area and large middle flood excavation area.(4)The method of sloping and lifting is adopted in Hekuan Xiatan,and the effect of shoal and the effect of drowning are studied through different excavation and dam arrangement and filling method.(4)A recommended scheme for the rapids group is proposed.It is combined into a new remediation plan of the rapids group through the optimization of different rapids.After analysis,there is still some difficulty in the upward movement of ships under the condition of medium and low water flow.But there are obvious improvements in the obstructing flow such as surf and the improvement effect is obvious.When Q?2225m~3/s,this river section of the project basically meets the requirements of self-sailing.But in disorder flow area such as Hekuan Shangtan,Hekuan Xiatan and#3,it is suggested that ships will not be meeting and sail by single line when the overall remediation plan is used.When Q>2225m~3/s,it is difficult for the ship to sail on the rapids.Considering that 2225m~3/s is the flow rate of P=5%in recent 3 years,it is suggested as the highest regulation navigable flow rate.