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The Hydraulic Characteristics and Efficiency Assessment of the Slit Dam in its Prevention Against Debris Flows
relative opening width
volumetric concerntration of sediment
This dissertation is based on the concept of sediment transport mechanics theory and incipient motion of gravel particles, and the theoretical model of volume concentration of the solid in debris flow before passing sabo dam was erected. The model indicates the relation between volume concentration of the solid in debris flow and the channel slope. Also the interaction mechanism between volume concentration of the solid and sediment flow rate is obtained through experimental flume. By using the efficiency assessment such as sediment flow rate, volume concentration ratio of the solid, storage of dam and volume concentration of the solid in debris flow before passing sabo dam, the design flowchart and design model of the width of the sabo dam can be constructed. For different sediment flow rates, the different width of the sabo dam can be easily designed. Also for the safety of the down-stream protection area, the sabo dam is required to transfer debris flow to less harm sediment flow. The design model of dam width and sediment flow are developed for the engineering design reference. According to the opening width of dam, the summation opening width of dam and effective dam height, a sample case is studied. This case includes the channel slope, geometrical condition and bed material data to indicate the determination steps designing flowchart of sabo dam. Further more, the regular changes of sediment quantity and quality of debris flow after passing sabo dam are studied by experimental flume and theoretical proving, and the results show that the smaller volume concentration of sediment passing through sabo dam has the stronger sediment flushing effect at downstream is found. Also when the sediment flow rate of debris flow is high, the sediment content is high due to the high quantity of carrying sediment. This will result in smooth tendency of flushing at downstream. Besides, the critical dam width at upstream hydraulic sediment sluicing can be obtained, according to the sediment accumulation at dam opening. The bigger the opening is the lower storage effect will be. At the dam opening the solid sediment usually forms a circle cave of 1/4 ball body, and the sediment will be cleared when sufficient water flow at upstream is available.
|Appears in Collections:||水土保持學系|
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