Experimental Research On Mechanism Of River Dredging For Deposition Reduction And Dredging Channel Geometry Parameter

The lower reaches of Yellow River are serious shrinking ones. Especially for resent years, because the conditions of coming discharge and sediment have occurred un-corresponding variation, shrink's velocity increases serious rapidly, shrink's characters tend to be serious, the river bed have been heightening continuously, from these, they have lead to various disaster effects obviously and brought heavy pressure for flood control and river harnessing. Moreover, the sediment deposition is the largest problem of the Lower Yellow River. Therefore it needs to adopt multiple harnessing measures for decreasing deposition in the Lower Yellow River. The comprehensive harnessing of "retaining, draining, discharging, regulating and excavating " and measures of sediment utilization have been pointed out. Dredging river for deposition reduction is one of the key methods but the key technology of dredging river for deposition reduction is still short of systematic research and demonstration. For recent years, in view of the effects of deposition reduction of river dredging and key technology in the Lower Yellow-River, a series of key tasks on special topics have been carried out by many researchers. And a series of research results have been obtained. This paper will combine with research results mentioned above to analyze as well as emphasizal analyze results by means of physics model' test, and demonstrate the effect of dredging channel' geometry parameter on deposition reduction of river dredging and mechanism of deposition reduction of river dredging. Thereby it generates anactive effect in this field and production practice of dredging river. Through analyzing and demonstrating, the knowledge of several aspects has been obtained as follows:1. The role of deposition reduction in definite reaches and interval has been played with dredging river in the narrow reaches of Lower Yellow River. It shows that the water level in the definite reach is lower than that with same discharges before dredging river, the surface slope on upper reaches dredged is enlarged and deposition load on bed is reduced or eroded.2. The bulk of effect on dredging river for deposition reduction is relative to chosen datum of dredging channel geometry parameter. Geometry parameters include dredging channel length, morphology of transversal section and longitudinal slopes.3. The drop datum of largest water level in researched reaches increases relatively with length increase of dredging channel in definite condition of discharge and sediment and definite dredged sediment quantity or dredged morphology of transversal section. But when the dredged length have increased to a certain value, the increment of water level drop datum decreased continuously with length increase of dredging channel. In other word, unit length increment tends to slowly. When dredging channel length is in a certain datum region, the effect of dredging sediment for deposition reduction is better relatively. Under the condition of testing discharge -sediment and dredging sediment quantity of 3380000m3, when dredging channel length is about 10km, the effect of dredging channel for deposition reduction will be rather better.4. The effect of dredging channel for deposition reduction is related to dredged channel geometry morphology and dredged channel area. The experimental research shows that the more wide-shallow the dredged section size is, the bigger the back-deposition ratio will be. But when the dredged section is overnarrow-deep, the back-deposition ratio will be increasing with decreasing of wide-deep radio. Therefore dredged section's wide-deep radio will be a good value adopted as well. Under the chosen conditions of testing discharge-sediment and scheme of dredged section, the effect of dredging river for deposition reduction will be considered better when the dredged section's wide deep radio is -^B~nlhn with 6~9 and dredged section area is about 250~300m2.5. The effect of deposition reduction...