Analysis Of Variation Of Water And Sediment Yield In Different Source Areas And Its Effect On Fluvial Response In Lower Yellow River

Based on the Digital Yellow River Model (DYRM), the thesis focuses on the simulation of the whole process of sediment yield and transport in the Yellow River. This work would be helpful to analyze the response law between water/sediment variation in the middle source areas and fluvial response in the lower channel.The DYRM can simulate the runoff and sediment yielding process on slope and the transport process of sediment-laden flow in gullies and fine channels. For the simulation of the whole process of sediment yield and transport in a drainage basin, it still needs a model to simulate the flood propogation in the main channel. The first part of the present work was to build a one-dimensional model to simulate the propogation of hyperconcentrated flood in the Lower Yellow River, which is adopted to investigate the fluvial characteristics of the Lower Yellow River. The second part of the present work was to develop a downscaling method to reproduce rainfall series with one hour time step, as the temporal resolution of observed rainfall data at gauging stations can not satisfy the requirement of simulation. The proposed method was based on the statistics characters of rainfall in the drainage basin. And the generated hourly series of rainfall data by the proposed method has the same statistic characteristics with the observed hourly data, and can be used as the input data in simulating the rainfall-runoff and sediment erosion in hydrology simulation.The observed data of 152 flood events in the Lower Yellow River, occurred between 1950-1960 and 1969-1985, was analyzed to explore the relationship between the flood from the water/sediment source area in the middle reach and the degradation/aggregation characteristics in the lower channel. The analysis showed that, the water and sediment coming from the drainage area between Hekouzhen Hydrology station and Longmen Hydrology station, also including Beiluo River and Malian River, had significant influence on flood aggregation in downstream river channel. Based on the requirement of numerical simulation with DYRM, this thesis modified the division of drainage areas upper Huanyuankou Hydrology station in the Middle Yellow River basin. And the Zone II in the modified division covers the drainage area of area between Hekouzhen Hydrology station and Longmen Hydrology station, Beiluo River and Malian River. More efforts were focused on withdrawing and numbering of the river network in Zone II, as a preparation for the simulation of the whole sediment yield-and-transport process through using the DYRM.The DYRM was run to simulate the process of water and sediment yield on slopes in the Middle Yellow River basin, considering the drainage division of water and sediment source areas. The simulated water and sediment hydrographs at Longmen Hydrological Station were used as the upstream boundary condition in the developed one-dimensional model for simulation of flood routing in the Lower Yellow River. The comparison between the simulated results and the observed data of the flood events in 1977 demonstrated that the coupling of the DYRM and the developed one-dimensional model is feasible in simulating the whole sediment process.The present work was a foundation for analyzing the responses law between water/sediment yield from different source areas in the middle reach and the fluvial response in the lower reach in the Yellow River basin.