Trench Effect Of The Lower Yellow River Dredging Conceptual Model For Research

According to many years practice in the Yellow-river harnessing, the comprehensive regulation measures such as "holding, drainage, adjustment, discharging and excavation" has been proposed in the book of << the compendium for the Yellow River management exploitation planning>>in 1997. Being one of these strategies, the "excavation" has been recognized as the basis measure to deal with sedimentation of the Yellow River. Based on relevant experiment, the best way of how to excavate will be given in this paper.First the author memorized the Yellow River excavation history and concluded development of modern dredging science, and found that most researches of dredging are related to navigation regulation, little used to flood control especially in the Yellow River with silty.Based on the experiment of generalized physical model of the lower reach of the Yellow River, and the study of the loaden flow mechanism and the dredging efficiency, the author get some new ideas as follows:1. Based on the appraisal of three kinds of means that reflect the effect of dredging, proposed several judging indexes (such as dredging efficiency) to estimate excavating results.2. Through studying the effect of the dredging length, found that it is not a linear relationship between the dredging length and the relatively reduced deposition, for example when dredging exceed a certain length, though the relatively reduced deposition still increase slowly, the depositing volumes begin to decrease. Therefore the optimized dredging length is about 10km.3. According to the experimental datum, studied the dredging dimensions and the dredging slope that give influence on flow velocity, sediment concentration, scouring and depositing volumes, water level and dredging efficiency etc., indicated that in a certain circumstance, the dredging cross-section is narrower-deeper is better. And give the range of B/H for 5-8, the optimized dredging slope is 1/1000.4. Using rational dredging dimensions can improve the excavation efficiency. For this generalized physical model, the excavation efficiency can up to 0.95, the relevant dredging dimensions are 200-300width, 2-3deepth,10km length and 1/1000 slope.5. Based on the physical model, summarized the general mode of river development in excavated segment with its up and lower influence reach after dredging, it means that gradually deposit in dredging segment while wash out in up reach, and the change intensities are weakening as the time goes on. The author also synthetically analyzed each effect factor on dredging, concluded several relationships between dredging dimensions and efficiency as formulae 7-1. 7-2 and 7-3.