MATEC Web of Conferences 246, 01019 (2018) https://doi.org/10.1051/matecconf/201824601019 ISWSO 2018 Variation on sandbar of tributary in Xiaolangdi Reservoir on Yellow River, China LI Tao1，2 ZHANG Jun-hua2 GAO Guoming1，2 Ma Huaibao3 1 Yellow River Institute of Hydraulic Research,YRCC,Zhengzhou, China,450003；2State Key Lab oratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wu han, China,430072) Abstract: Sandbar development would stop the water and sediment exchange between main river and tributary and even influence the normal reservoir opeartion. From the surveyed data of reservoir built many years ago, it shows that when there is a bar in tributary mouth, the tributary volume below the bar will become nullification during the period of flood control or water and sediment regulation of reservoir. There are more tributaries in Xiaolangdi reservoir than the others that it occupies 41.3% of the total initial volume of tributary volume. Obviously, the effective use of tributary volume has been important influenced by comprehensive utilization efficiency of reservoir scheduling, such as flood control, sedimentation reduction and comprehensive utilization. Results of Xiaolangdi Reservoir mobile-bed physical model experiments show that tributary is equivalent to lateral extension of river bed, the tributary intrusion deposition process have strongly relations with the factors, such as original topography, river bed deposition shape and its regime, process with input discharge and input sediment, and method of reservoir regulation. The variation trends of main river and tributary terrain forecasted by model test are basically in accordance with field surveyed data. The results could be used for research, design, and forecasting of reservoirs in sediment-laden river. surveyed data from built reservoirs are analyzed in analogy,the research results of sandbar variation in long 1 Introduction series model tests in the first stage of late retainning Tributary sandbar often occurs at the mouth of tributary sediment period of xiaolangdi reservoir is condensed.The which lie in a disadvantageous site.With reservoir results could be technically refered by the sediment-laden operation,if there are little possibility for tributary flood river planed,designed and operated and poor water and sediment input match from main river,large scale sandbar forms at the mouth of tributary 2 Overview of Xiaolangdi Reservoir and with interrupting the water and sediment exchange its physical model between main river and tributary and influencing the reservoir operation precision.For example,sandbar Xiaolangdi Reservoir belongs to canyon-Reservoir, and development in the mouth of Guishui river in Danjiangkou the upper reach is wider in than that in lower reach. reservoir,stops the water supply from the reservoir. According to the plane modality, the reservoir could be Sandbar development in the mouth of Wei river indued by divided into two parts. The upper reach is from Station the Yellow river,heavens the flood threat and water Sanmenxia to Section HH37 with the length 60.92km and environment pollution in the Wei river valley. Sandbar bottom width of river valley about 200m to 400m. The development in the mouth of Yuan river and Longmen lower reach is with the length 62.49km and bottom width river brings many problems.From the bulit reservoirs with of river valley about 800m to 1400m,especially bottom long term practical operation,sandbar stops the water and width of river valley about 300m between 27km and 31km sediment exchange between main river and tributary ,and to the dam. The normal water storage level is below 275m reservoir capacity of tributary can not be used with the original volume 12.750 billion cubic metre and effiency.Even the reservoir general utilization benefit branch volume 5.263 billion cubic metre which occupies would be heavily hindered.By now,water and sediment 41.3% ratio of the total volume. The quantity of branches movement law have not been controled and which volume is bigger than 0.1 billion cubic metre is modeled.From the study on the physical model of 11.These branches all distribute the lower reach of the Xiaolangdi reservoir by Zhangjunhua[9-14],the deposition reservoir. The main characteristics are listed in Tab.1. in tributary which is mainly induced by turbidity current The designed effective storage capacity of reservoir is had been found with further study on the backward flow 5.1 billion cubic metre.The effective storage capacity and between main river and tributary. With the help of field the quantity of branch sediment storage occupy both the © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 246, 01019 (2018) https://doi.org/10.1051/matecconf/201824601019 ISWSO 2018 correspondent total quantity above 30%.It will influence combination with gradually hightening pond water level the general utilization heavily including reservoir anti- for flushing fine sediment and retaining coarse sediment flood and sedimentation reduction whether the branch and water and sediment regulation.Selection of storage is effectivly utilized.The tributary has a small daily opportunity for scour due to dropping pond water level discharge and almost blanking.some sand and little stone occasionally decided on the period,when reservoir will flow downstream when short periond flood comes sedimentation comes 4.2 billion cube metre ,the max during the flood period.According with analying,the regulating discharge is 3700m3/s and the min regulating transporting quantity of bed material and suspend sand per discharge is 400m3/s.Then flood process is made with the y quantity ear is respectively 0.27 million tons and 2.97 minimal water storage meets 1.3 billion cube metre. When million tons.it could be ignored with the input sediment the input discharge quantity. Therefore, the branch sediment storage could meet the designed quantity or not ,which is decided by the quantity of the incoming sediment from the main to the 275 tributary.Morever,the sedimentation distribution of the branch mainly influence the effective storage 255 capacity.When the sediment from the main stream comes Elevation/m into the branch, sand bar often occurs at the mouth of 235 branch.The storage capacity of branch below the sand bar elevation is not be effective utilized. Even it would 215 become invalid volume which neither intercept sediment 2007.10 1 nor participate in normal operation.According to the 2 3 195 surveyed data before the flood period in 2015,the 4 10 17 difference between sand bar and its river bed is beyond 10 meters in the biggest branch named River Zhenshui. 175 0 20 40 60 80 100 120 The physical model of Xiaolangdi Reservoir covers Length to the dam/km about 124km from Station Sanmenxia to the dam,which has the total main river volume and 90% of branch volume.it had been designed by use of similar condition Fig.1 Chart of process on main channel talweg on the sediment-laden reservoir movable bed model and prediction ahead 2 days is not less than 2600 river bed boundary feature.the main scale is listed in the m3/s,reservoir door is opened for scoured or flood process Tab.2，which is decided by the validated experiments with is made by water supplement with storage.When the sum the field data from Xiaolangdi reservoir. The model is discharge of the input and Station Heishi and Station 3 designed by the vertical scale 100 and horizontal scale Wuzhi downstream is more than 4000m /s,the reservoir is 60.The Zhengzhou thermal power plant fly ash is chose as shifted into the anti-flood operation state. model sand. Tab.1 Main characteristic of branchesin Xiaolangdi Reservoir Day Zhens Shiji Dongy Xiya Yan Boqi 4 Landform variation process on water- river name u hui ng ang ng xi ng sediment series model experiment Length between mouth and 3.9 18.0 22.1 31.0 41.3 54.0 57.6 the 4.1 Landform variation process in Main River dam/km Original 0.57 1.767 0.48 0.23 0.40 0.13 The reservoir initial boundary condition is delta landform volume/bi 0.3111 97 2 04 53 71 89 llion m3 in October,2007.The peak of delta is 27.2km to the dam.The fore slope reach below the peak of delta has a Tab.2 Main scale table sharply increaseing water depth,sharp decreasing velocity settling Sediment Horizontal vertical Velocity roughness time velocity concentration and sediment-carrying capacity sharp drop.On the process 300 60 7.75 0.88 1.34 1.50 44.9 of experiment,much sediment settle down and delta continue going to the dam.At the No.5 year, the peak of delta transformed into cone and only erosive funnel 3 Model experiment condition existed in the front of the dam.After that,during the process of reservoir water and sediment regulation,river Based on the surveyed surface topography of Xiaolangdi bed gradully rised and the slope was to slow down. At the Reservoir on October,2007,with 17 a water-sediment No.14 year,in the flood period,the flood beach face series from 1960 to 1976 designed the 2020 level, elevation came to 254 metre and the accumulated experiment on operation mode of Xiaolangdi Reservoir in deposition was about 7.55 billion cube metre.Then the its second stage of sediment retaining had been carried in sediment retaining period was over and normal operation use of operation mode which can achieve sediment period began. At the No.17 year, the operation mode of pluriennial regulation and scour due to dropping pond scour due to dropping pond water level occasionally water level occasionally.