【作者】 段光磊；

【导师】 张小峰；

【作者基本信息】 武汉大学 ， 水力学及河流动力学， 2012， 博士

【摘要】 大量的数学模型、实体模型和水工程泥沙试验、河道整治、航道整治研究等,均建立在河道实测冲淤变化资料的基础上,因此河道的冲淤数量及其分布是科学试验、工程调度和河道演变及整治研究的重要基础资料。断面地形法、网格地形法和输沙量平衡法是计算河道冲淤量广泛采用的三种模式。而在生产实践中,分别采用断面地形法和输沙率量平衡法计算的同一河段、同一时段冲淤量往往差别很大,甚至部分河段、部分时段存在冲淤性质相反情况。本文采用大量的实测水沙、地形资料,运用断面法、网格地形法和输沙量平衡法,计算了三峡水库蓄水后三峡坝下游宜昌至监利河段的河床冲淤量。对不同计算方法中影响计算精度的因素进行了研究。运用非线性分形理论对河床起伏程度与断面代表性关系进行了研究。对水文测验和河道测量观测布置提出了合理性建议。具体研究内容和所得主要结论如下。(1)河道冲淤量计算结果若要达到一定的精度,除在弯道、汉道断面宜布置相对较密的断面外,在河道急剧放宽和束窄的局部河段断面不宜太稀。若采用断面地形法计算宜枝河段河段冲淤量,断而间距不宜大于2倍河宽。断面面积采用椎体法和梯形法计算河道冲淤量,差异很小,两种方法均能满足要求。(2)随着网格尺寸增大,河道真实地形被“坦化”,局部地形的细微变化弱化,同水位级下河槽槽蓄量减小,河道冲淤量也呈减小趋势；利用地形测图数据进行网格地形法计算时,网格尺寸不宜大于地形施测断面点间距。对1：10000地形图而言,在60m以内为宜；对1：5000地形图而言,在30m以内为宜。DEM克里格法插值优于其他插值方法,能相对准确地还原原始地形。(3)采用长江水利委员会水文局临底悬沙观测试验资料,探讨了三峡坝下游实测悬移质输沙量改正问题。常规悬沙测验中,三峡坝下游河段悬移质泥沙测验需要考虑临底悬沙含沙量较大问题。另外,采砂河段需要准确的采砂量,分流河段要考虑分沙量和口门至水文站河道冲淤量。对实测成果进行修正后,输沙量平衡法才能得到准确结果,否则该方法计算的冲淤量明显偏小(4)采用分形几何理论和方法探讨了断面、河床表面起伏度与冲淤量的关系。得到：荆江河段固定断而间距大,弯道、分汉河段的固定断面控制不了地形变化,两种方法计算结果差异大。荆江局部河段固定断面代表性不强,需要适当加密固定断面,有些断面方向需要调整。冲淤量差值百分数及床面分形维数有一定的相关关系,床面分形维度越大的河段,网格法与断而法冲淤量差异也越大。(5)对三种不同计算方法精度进行了综合评价。影响输沙量平衡法计算精度的因素主要有低含沙量、冲刷河段临底悬沙含沙量大、采砂量估算误差和口常简测法输沙量测验的系统误差等。网格地形法计算精度主要有地形测量精度,特别是水深测量精度和局部不易实测的局部空白区,以及网格插值方法和分辨率大小等。断面法测量精度主要影响因素除断面测量精度,特别是水深测量误差,以及断面代表性和断面间距量算误差等。更多还原

【Abstract】 A large amount of research on mathematical models, physical models, sediment experiments, river training, and channel regulation is based on the data of channel scouring and siltation. Consequently, the amount and distribution of deposits are important basic data in scientific experiments, project scheduling and river evolution and regulation. The section topographical method, grid topographical method, and sediment discharge balance method are widely adopted in the calculation of channel erosion-deposition amount. In theory, the calculated results of erosion-deposition amounts should be equal or much the same with different methods within the same river reach and period of time, nonetheless, researchers have found it may not be the case in production practice as well as scientific researches.In this paper, the channel erosion-deposition amount of Yichang-Jianli river reach (which is located in the downstream of the Three Gorges Dam) after the impoundment of the Three Gorges Reservoir have been calculated based on a large number of measured water and sediment data as well as topography data, by using the section topographical method, grid topographical method, and sediment discharge balance method. Some factors influencing the calculation accuracy have been comprehensively researched. The nonlinear fractal theory has been used to study the relation between bed fluctuation degree and section representative. Reasonable proposals for arrangement of observational sections in hydro logical tests and channel measurement are put forward. Specific research contents and main conclusions are as follows:(1) If we want to achieve the calculation accuracy, sections should not be too few in contractive and expansive reaches, as well as bend and braided reaches. When using section topographical method, the distance between sections should be less than2times of river width. The difference between cone and trapezoid method in the calculation of sectional area is small, and both can meet requirements.(2)As grid dimension increases, the true terrain of river channel flats, subtle changes of local topography are weakened, storage capacity under the same water level reduces, and river channel erosion-deposition amount decreases. The grid dimension should not be larger than the distance between measuring cross-sections in calculation when topographic map is used. For topographic map with scale of1:10000, the grid dimension should be less than60m; and for topographic map with scale of 1:10000, the grid dimension should be less than30m; DEM Kriging interpolation is better than the others, and can simulate the original topography relatively exactly.(3) According to the observation data of close-to-bed suspended load from the hydrology bureau of the Changjiang Water Resources Commission, the problem of suspended sediment miss-measurement in the downstream of the Three Gorges Dam is discussed. Miss-measurement exists in the conventional suspension load test in the downstream of the Three Gorges Dam. In addition, accurate amounts of sand mining and sediment diversion are required in sand mining river reaches and distributary channels respectively. After the measured results are modified, the accurate results can be got by the sediment discharge equilibrium method, otherwise, the erosion-deposition amount will be obviously less.(4) The distance between fixed cross-sections in Jingjiang reach is large, and the fixed cross-sections in bend and braided reaches cannot control the terrain variation, thus the results of the two calculational methods have great difference. The representative of fixed cross-sections in local reaches of Jingjiang is not strong, and it’s need to increase fixed cross-sections and adjust the direction of some cross-sections. The difference percentage of erosion-deposition amount has a certain relationship with fractal dimension of bed surface. The difference of results between the grid method and the fixed cross-section method is bigger, as the fractal dimension of the bed surface increases.(5)The precision of three calculational methods are comprehensively evaluated. The main factors influncing the calculation accuracy of sediment discharge balance method include low sediment concentration, miss-measurement of close-to-bed sediment load in the scouring reach, the error of sand mining and the system error of the conventional sediment discharge. The main factors influncing the calculation accuracy of grid topographical mothod mainly include the topography measurement accuracy, especially the measurement accuracy of water depth and some local areas which are difficult to measure, as well as the grid interpolation method and the resolution ratio. The main factors influncing the calculation accuracy of section method mainly include the representative of the cross-section and the measurement error of section distance, apart from the cross-section measurement accuracy and water depth measurement error.更多还原