Sediment Transport

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  • Topic: Shear stress, Sediment, Sediment transport
  • Pages : 87 (16159 words )
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  • Published : May 7, 2013
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SEDIMENT

TRANSPORT

Zhou Liu

3. udgave.

januar 2001

Laboratoriet for Hydraulik og Havnebygning Instituttet for Vand, Jord og Miljøteknik Aalborg Universitet

Preface
Flow and sediment transport are important in relation to several engineering topics, e.g. erosion around structures, backfilling of dredged channels and nearshore morphological change. The purpose of the present book is to describe both the basic hydrodynamics and the basic sediment transport mechanism. The reader’s background should be a basic course in wave theory and fluid mechanics. Chapter 1 deals with fundamentals in fluid mechanics with emphasis on bed shear stress by currents, while Chapter 3 discusses wave boundary layer theory. They are both written with a view to sediment transport. Sediment transport in rivers, cross-shore and longshore are dealt with in Chapters 2, 4 and 5, respectively. It is not the intention of the book to give a broad review of the literature on this very wide topic. The book tries to pick up information which is of engineering importance. An obstacle to the study of sedimentation is the scale effect in model tests. Whenever small-scale tests, large-scale tests and field investigations are available, it is always the result from field investigations which is referred to.

i

CONTENTS

Contents
1 Steady uniform flow in open channels 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Types of flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prandtl’s mixing length theory . . . . . . . . . . . . . . . . . . . . . . . . . Fluid shear stress and friction velocity . . . . . . . . . . . . . . . . . . . . Classification of flow layer . . . . . . . . . . . . . . . . . . . . . . . . . . . Velocity distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 4 5 7 9

Ch´zy coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 e Drag coefficient, lift coefficient and friction coefficient . . . . . . . . . . . . 14 Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 17

2 Sediment transport in open channels 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8

Sediment properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Threshold of sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Bedforms, bed roughness and effective shear stress . . . . . . . . . . . . . . 22 Transport modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Bed-load transport formulae . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Suspended load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Total sediment transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 34

3 Wave boundary layer 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9

Concept of wave boundary layer . . . . . . . . . . . . . . . . . . . . . . . . 34 Laminar wave boundary layer on smooth bed . . . . . . . . . . . . . . . . 35 Wave boundary layer thickness . . . . . . . . . . . . . . . . . . . . . . . . 37 Wave friction coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Mechanism of sediment transport in coastal regions . . . . . . . . . . . . . 41 Boundary layer of irregular waves . . . . . . . . . . . . . . . . . . . . . . . 42 Boundary layer of wave and current: Fredse’s model . . . . . . . . . . . . . 42 Boundary layer of wave and current: Bijker’s model . . . . . . . . . . . . . 47 Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 50

4 Cross-shore sediment transport and beach profile 4.1

Sediment size and its sorting on beaches . . . . . . . . . . . . . . . . . . . 50 ii

CONTENTS

4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9

Threshold of sediment under wave actions . . . . . . . . . . . . . . . . . . 51 Depth of closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Bed form...
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