| The riverbed development of Yichang section, water level change and itsinfluence to lock and channel, the countermeasure were all researched bymany kinds of technological means of testing, such as the analysis ofmeasured data, flume test, mathematics model calculate, model test,ship-model sail test and so on. The main content is as follows:Based on the critical condition when sediment begin to move, normaldistribution property of instantaneous velocity as well as velocity distributionin exponential, the formula of the incipient velocity including incipientprobability for non-uniform sediment is developed in this paper. The exposureand shelter of non-uniform sand is taken into account by introducing acoefficient. The equation of incipient velocity was verified by Yichang andCuntan gauging station on the Changjiang river, and calculated velocitieswere in agreement with measured data. Besides, the incipient standard ispresented.The whole sand model were set up by adopting the methods of changes ofhe diameters scale, the result shows that the method were satisfactory., it canbe used into the design for similar river model.By flume test to the serials of submerged-dams, some equations werefirst present, such as the local roughness coefficient, the height of backwater,the space for the dam, the flow velocity of the cross-section of the dam, theinfluence of the number of dam on the water level and flow velocity. All ofequations can calculated the effect of the submerged dam regulationThe result of analyzing the field data indicate that the dropped speed ofwater level of Yichang station was quickly from the Gezhouba dam were builtin 1981 to 1988, after that, the dropped speed were not as quickly as before,water level was maintain the range of 37.9～38.0m, the depth of Sanjiangchannel was only 3.0m, it don't meet the design depth of 4.5m demands .The series tests (from 2003 to 2012) on move bed model indicate asfollowing. During the stage of reservoir operation at 135m, the course oferosion will be finished basically, and the amount of erosion can reach about6,100,000m3 during this stage, and erosion area located in the riverbed oflower level, local erosion depth can reach to 5.0m-7. 0m;During the stage ofreservoir operation at 156m and 175m, the amount of erosion is greaterslightly than that of the deposit in the whole section river, the rules ofdeformation of riverbed take as the characteristics of erosion and depositalternative along the river. At the same time, the water level of Yichangstation will only reach respectively to 37.65m, 37.50m and 37.36m by the endof 135m, 156m and 175m of the conservation stage of the Three GorgesProjects, and the depth of Sanjiang channels and ship-lock No. 3 is about only2.5m, the result shows that Sanjiang channels of Gezhouba will face the threatof stopping navigation if any measurement will not be taken.To resistance the bed erosion, some research tests, for example thescheme of river bottom protection and the regulation engineering ofsubmerged dam, were done on the move bed model. The test result shows thatthe scheme of river-bed protection is not available because the water levelafter engineering is basically equal to that before. According to therelationship of space of submerged dam which was obtained by flume test, thespace of submerged dam at finally were determined between 350m and 450mafter reconfirmed the space again and again on the physical model, and theelevation of submerged dam should be 6.0m under water level whichcorresponds to the design discharge. The plan was tested on the physicalmodel, and the result indicates as following. During the stage of reservoiroperation at 135m, the water level in Yichang can reach to 38.0m basically atthe design discharge Q=3200m3/s, During the stage of reservoir operation at156m and 175m, the water level can reach respective to 38.5m and 39.0m ifthe minim draw off discharge of three gorge are respective more than 4300m3/s and 5300 m3/s. The result shows that the regulation engineering ofsubmerged dam can meet the demands of navigation in different stage ofreservoir operation. If this measurement were not taken, then the water levelcan't meet the navigation condition unless draw off discharge at least need tobe 3900 m3/s, 5000 m3/s and 6300 m3/s in different reservoir operation stage.So the benefit of this plan is equal to add the discharge 800～1000m3/s,namely put off the navigation periods about 30-40 days, the project benefit iscomparatively obvious. In addition to this, the project is also benefit toDajiang channel, it can decline the slop of water level, slow down the flowvelocity, so it is useful for Dajiang channel to meet the navigation condition.Ship-model test indicate, the submerged dams make the local slop ofwater level and local velocity greater than before, produce weak pondingbetween each dam, but the velocity of flow between the dam group isrelatively slow, also the length of range of head fall is smaller than length offleet, so the project of submerged dams will not influence obviously tonavigation of fleet... |
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