Abstract:

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.

Key words: riverbed, erosion-deposition amount, calculation method, fractal dimension