河道实测冲淤量不同计算方法结果比较分析

在生产实践中,采用不同计算方法得出的冲淤量结果往往差别很大,部分河段、部分时段甚至存在冲淤性质相反情况。采用大量的实测水沙、地形资料,运用断面地形法、网格地形法和输沙量平衡法3种方法计算了三峡水库蓄水后三峡坝下游宜昌至监利河段的实测河床冲淤量,对不同计算方法的计算结果和影响计算精度的因素进行了分析,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。研究结果表明输沙量平衡法需对悬沙测验成果进行改正,并考虑泥沙测验定线误差、水量不平衡、河道采砂和分流洪道冲淤;断面地形法需在弯道、汊道、河道急剧放宽和束窄的局部河段布置相对较密的断面;网格地形法需选择适宜的插值方法,且网格尺寸不宜大于施测断面点间距。

Comparative Analysis on Riverbed Erosion and Deposition Amount Calculated by Different Methods

In practice, the amount of riverbed erosion and deposition in the same reach or in the same period calculated by different methods differs significantly from each other. At present, the calculation methods by using cross-section morphological variation, DEM grid morphological variation, and sediment balance are widely used. The amount of riverbed erosion and deposition in the reach from Yichang to Jianli of Yangtze River downstream of Three Gorges Project after impoundment was calculated using the above mentioned three methods based on topographic map, cutting cross-section on topographic map and sediment data of hydrologic stations. Furthermore, the calculation results and the factors affecting the calculation accuracy were analyzed, and the nonlinear fractal theory wasused to study the relation between riverbed fluctuation degree and section’s representativeness. Research results suggest that to improve the sediment balance method, suspended load near riverbed needs to be modified, and the alignment error of sediment measurement, water imbalance, sand mining and sediment diversion should be taken into consideration; as for the method of cross-section’s morphological variation, relatively close sections must be laid in river bends, bifurcated reaches or contractive and expansive reaches; while appropriate interpolation method must be employed for the method of grid morphological variation, and the grid space should be no larger than the distance between measuring points.