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Title: Bed erosion around obstructions in rivers
Author: Gill, Mohammad Akram
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1970
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An experimental investigation has been made for the determination of the equilibrium depth of scour of sand beds in a long contraction (contraction ratio,i-e the ratio of the contracted to the width of the uncontracted channel, was 2/3) and around spur dikes with blockage ratios ( ratio of the length of spur to the width of the channel) of 0.I339 0.267 and 0.40. Two grades of quartz sands have been used. A simple analytic approach first proposed by L.G. Straub (4I,42) for a long contraction was examined and found adequate for the prediction of scour depth in the long contraction. It has been shown by the present experimental results that the same approach can be applied for the prediction of scour around a spur dike, with an empirical coefficient which depends appreciably on the flow depth in the channel and weakly on the size of the bed materials used herein. Some experiments were also done on erosion around a spur dike by fixing the entire upstream and downstream channel beds excepting a 3 ft. long test section which was composed of loose incoherent sand. The object was to see as to how the scour depth would be affected when the bed shear stress in the upstream channel is increased beyond the critical shear stress of the bed material but no sand is externally fed into the flow. The results have been compared with those obtained from the experiments on loose sand beds. An analytic steady state solution for the speed and the height of bed waves has been obtained from a linear approach. The expressions obtained for the height of bed waves are similar to the one previously proposed by Yalin on the basis of an inductive argument.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available