Mechanics of bed-load transport and the characteristics of rippled beds, with special reference to channel roughness

• Main Author: Khalil, Mohamed Bakr
• Other Authors: White, C.M
• Published: Imperial College London 1963
• Subjects: 532
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602234

This thesis treats a subject that of late has become deeply interesting and important not only to field engineers, who need its information for practical problems of a varied nature in river hydraulics, but also to geologists, geographers and others. As presented here it, however, treats the subject from the point of view of engineers. The thesis deals with the transport of sediment as bed-load in open channels, the formation and development of ripples and their influence on the flow resistance. A theoretical approach to the transport of sediment is presented where the bed-load is expressed as a function of the stress. The bed-load relation was found consistent with experiments on a preserved flat sand bed, where the grain speed and concentration were photographically recorded, though anomalies were apparent when applied to tests on a mobile boundary. The formation of ripples appreciably affected the transport rate through a number of actions, and entailed the introduction of a corrective factor. The speed of transport of the load is correlated to the flow and the grain concentration. The mechanistic approach to bed-load transport brought out a plausible explanation for the origin of ripples founded on experimental evidence. The thesis deals also with the main aspects of ripples, which are of special interest to river engineers. The factors governing their shape, growth, alignment and stability were discovered and criteria for their dimensions are given. It was revealed that the transport of bed-load could be inferred by simple measurements of ripple dimensions and the velocity of ripple migration. The problem of flow resistance is then discussed and it is disclosed that the bed-load transport contributes slightly to the energy loss, not due to its transport but to a change in the surface texture; whereas ripples add considerably to the energy loss. An approach for predicting the coefficient of resistance for rippled beds is given.