Fluvial Processes in River Engineering

Fluvial Processes in River Engineering

by Howard H. Chang, San Diego State University

The book was published by John Wiley & Sons, New York, NY in 1988.

It may be purchased from Krieger Publishing Company, P.O. Box 9542, Melbourne, FL 32902-9542, Ph: (407) 724-9542, FAX: (407) 951-3671

or from amazon.com

PREFACE Back To Top

Rivers have been a focus of human activities throughout ancient and modern times. So important to mankind are the benefits obtained from rivers, and so necessary is the protection against floods and other river disasters. While engineers are interested in water supply, channel design, flood control, river regulation, navigation improvement, and so on, it has been clear that rivers, as a part of nature, can be mastered not by force but by understanding. Rivers have been a subject of study by engineers and scientists who have been fascinated by the self‑formed geometric shapes and their responses to changes in nature and human interferences. In addition to engineering, understanding river behavior is also necessary for environmental enhancement. Few other subjects have been studied more extensively than rivers, yet some major aspects of the hydraulics, sedimentation, and fluvial processes have only become clear to us in recent years. Of course, many more aspects are yet to be understood.

River flow is a type of open-channel flow because of the free surface. Considerable knowledge is required to make a determination of the free surface for rigid channels. But all boundaries of a river are free surfaces, a fact well described by Kennedy (1982). The hydraulics and fluvial processes of rivers are far more complex than rigid channels. For example, analytical determination of the self‑formed width and its adjustments has only become possible in recent years. Width formation is one aspect of fluvial processes to which other aspects, such as depth and meandering pattern, are closely related.

Recent development in river research has substantially extended beyond the hydraulics of sediment transport, stimulated by the abundance of erosion and sedimentation problems. Much progress has been made to provide analytical methods for alluvial channel design, river morphology, and mathematical simulation of river channel changes. My motivation to write this book stems from recent advances, which need to be assembled in book form.

Fundamental principles and applications are presented in this book. Because of the close interrelationship between river engineering and fluvial geomorphology, geomorphic approaches are integrated with the engineering principles. The river as a part of the fluvial system is also analyzed from the system point of view. The selection of key references and the bias of this book are dictated by my personal experience and interest, which may be different from those of others.

Through teaching, research and consulting, I have come across different problems that require engineering analysis and solution. Approaches to solving these problems have been developed by engineers and scientists, including myself. Underlying such approaches are the common principles for river hydraulics and fluvial processes. The large variety of problems covered in this book are actually governed by common principles of fluvial processes.

This book is intended primarily as a textbook for civil engineering students at the senior or graduate level, to be used in a course on river and sedimentation engineering. The materials in this book may be covered in three to five units for college credit. Suggested prerequisites for this book include basic training in mathematics (calculus and differential equations), computer programming and basic hydraulics. This book is also a reference book for professionals directly involved in flood control, sedimentation, fluvial processes, bridge design, waterways, irrigation, and so on. It may also be useful for researchers in hydraulics, agricultural engineering, geomorphology, environmental sciences, and geography.

My initial fascination with regard to rivers was attributed to the stimulation by Daryl B. Simons and Stanley A. Schumm, to whom I am greatly indebted. I am also very grateful for the ideas obtained from professional associations with Joseph C. Hill, V. Miguel Ponce, Vito A. Vanoni and C. Ted Yang.

BOOK COVERAGE Back To Top

The subject of this book is river flow, river channel formation, the physical characteristics of rivers, responses of rivers to natural and human-made changes, and analytical methods of design and evaluation. A comprehensive presentation of river processes and engineering must be built upon the foundations of fluvial geomorphology, hydraulics of river flow, and sediment transport. On the basis of this logic, this book is organized into the following five principal parts:

Part I. Fluvial Geomorphology

Part II. Foundations of Fluvial Processes for Rivers

Part III. Regime Rivers and Responses

Part IV. Mathematical Modeling of River Channel Changes

Part V. River Engineering

Part I, which is on fluvial geomorphology, presents an overview of the fluvial system, including the river and its drainage basin. This part covers fundamental materials related to rivers (developed following essentially the geomorphic approach) such as the variables for alluvial rivers, the regime concept, channel-forming discharge, river classifications, hydraulic geometry, meander plan form, thresholds in river morphology, and geomorphic analysis of river responses. These topics provide the general framework and set the stage for more in-depth and analytical treatment of river processes. Geomorphic principles described in this part will be extended by engineering approaches in the remainder of the book.

River channel formation and responses to change are direct results of the complex interaction of the flow and its boundary. Physical and analytical foundations of such fluvial processes are presented in Part II. Major topics include open channel hydraulics, physical properties of sediment, scour criteria and scour-related problems, alluvial bed resistance, sediment transport in rivers, and flow and sediment processes in curved channels. These subjects provide the foundation for the comprehensive study of rivers. Such materials are typically covered in a standard textbook on sedimentation. This book incorporates recent advances in these subjects. It also includes the subject on flow in curved river channels which is usually not included in a book on sedimentation. While materials presented in Part II serve as the analytical bases for the remainder of the book, they are also useful in engineering analysis because they stand alone.

Part III is on regime rivers and responses. While important empirical methods are included in the book, the thrust is on the analytical approach to determine the basic parameters for the hydraulic geometry of alluvial rivers under the dynamic equilibrium and to quantify the fluvial processes of river channel formation and adjustments of equilibrium. In this coverage, basic physical relationships for river channel formation are first outlined. They are then applied to develop design methods for stable alluvial channels and to establish hydraulic geometry for natural rivers. Complete analyses are provided for the important features of alluvial rivers, such as channel geometry, river meanders, channel patterns, and the thresholds with regard to distinct characteristics of river channels. A unique feature that is included is on the quantitative prediction of channel response to change, illustrated by case histories.

[1] The plan form of river meanders and the processes of migration are also covered in Part III. The process that characterizes the flow through meanders is the streamwise variation of the helical motion or secondary currents, to which many features of river meanders are related. Analytical determination of the self-formed meander plan form is based on the streamwise variation in secondary currents.

Part IV is devoted to mathematical modeling of alluvial channels, in which modeling techniques and applications are described and illustrated by case studies. The scope is on quasi two-dimensional modeling to simulate fluvial processes in river channels with a changing boundary. River channel changes so simulated include channel bed scour and fill (or aggradation and degradation), width variation, and changes in bed topography induced by curvature effects. The mathematical modeling has its physical foundation in the fluvial process-response, which is characterized by the river's constant adjustment toward dynamic equilibrium subject to the physical constraints. In response to a natural or human-made change, the transient behavior of an alluvial river is reflected in its adjustment toward dynamic equilibrium, although the dynamic equilibrium may never be attained in nature because of the changing discharge.

Mathematical modeling is presented in modular form, with major components of water routing, sediment routing, and simulation of river channel changes. The physical foundation and modeling techniques for each component are described in detail.

A variety of transient problems for erodible channels are elucidated using the approach of computer-aided study, including general scour at bridge crossings, gradual breach morphology, erosion and deposition induced by instream sand and gravel mining, tidal responses of the river delta system, water and sediment routing through curved channels, fluvial design of river bank protection, and stream gaging of fluvial sediment. Several field tests of modeling studies are also presented.

Part V, which is on river engineering, is devoted to engineering measures for achieving river training, including bank protection, dikes, grade-control structures, and so on. Each measure is illustrated by examples.

SPECIAL FEATURES Back To Top

This book is one of the first to present a complete analytical treatment of river morphology and its responses to environmental and human-made changes from the engineering point of view. This comes about because of recent advances on the analytical determination of the regime width of rivers and transient adjustments in width. Basic principles underlying fluvial processes are summarized.

Computer modeling of alluvial rivers and its applications are within the theme of this book. This approach has been a focus of recent research and development in this evolving field. From a sound physical foundation, mathematical techniques are employed in this book to integrate those convoluted physical relationships into a model for simulating river channel changes. Computer-aided analysis and design for river projects are illustrated by abundant examples. Such applications are especially useful for large rivers whose natural geometry would prohibit the traditional approach.

In addition to engineering application, mathematical modeling is also valuable for researchers who have been helped by the computer to understand physical phenomena and to test hypotheses. My research has been greatly benefitted by the countless trials made on the computer.

This book presents considerable discussion on the flow and sediment processes in curved channels. In addition to the mechanics of flow in the channel, it also associates the channel morphology, such as meander plan form and bed topography, to the secondary currents inherent in curved channels.

This book presents materials that are related to engineering design. Such design-related topics are included in many chapters, from traditional design methods to computer-aided channel design.

Predicting channel response to change, whether caused by nature or human interference, is important in river engineering and environmental studies. This book is unique in presenting quantitative methods for predicting river's long-term adjustments in regime as well as short-term changes during a flood event.

The basic topics of alluvial flow resistance and sediment transport are generally included in existing books on sediment transport. This book incorporates recent development and thus brings up to date such coverage. The subjects of sediment diffusion and sorting in nonequilibrium sediment transport are among the recent development in sedimentation covered in this book.

INTENDED AUDIENCE Back To Top

This book is intended primarily as a textbook for civil engineering students at the senior or graduate level, to be used in a course on river and sedimentation engineering. Such a course or related topic is usually in the civil engineering curricula. The materials in this book may be covered in three to five units for college credit. Suggested prerequisites for this book include basic training in mathematics (calculus and differential equations), computer programming and basic hydraulics.

This book is also a reference book for professionals directly involved in flood control, sedimentation, fluvial processes, bridge design, waterways, irrigation, drainage, etc. It is also useful for researchers in hydraulics, agricultural engineering, geomorphology, environmental sciences and geography.

References

Kennedy, J. F., "Reflections on Rivers, Research, and Rouse," J. Hydraul. Eng. ASCE, 109(10), pp. 1253-1271, October 1983.

San Diego, California

November, 1987

TABLE OF CONTENTS Back To Top

PREFACE

PART I FLUVIAL GEOMORPHOLOGY

CHAPTER 1 INTRODUCTION

1.1 The Fluvial System

1.2 Variables for Alluvial Rivers

CHAPTER 2 OVERVIEW OF RIVER MORPHOLOGY

2.1 Regime Concept

2.2 Channel‑Forming Discharge

2.3 Longitudinal Stream Profile

2.4 River Classifications

2.5 Thresholds in River Morphology

2.6 Hydraulic Geometry

2.7 Meander Plan form

2.8 Geomorphic Analysis of River Channel Responses

References

PART II FOUNDATIONS OF FLUVIAL PROCESSES

CHAPTER 3 HYDRAULICS OF FLOW IN RIVER CHANNELS

3.1 Shear Stress Distribution

3.2 Uniform Flow Formulas

3.3 Boundary Layer Regions

3.4 Turbulent Shear Flow in Channels

3.5 Fixed-Bed Flow Resistance

3.6 Flow Resistance in Gravel-Bed Rivers

3.7 Composite Roughness and Side-Wall Corrections

3.8 Energy Equation and Water Surface Profiles

3.9 Unsteady Open Channel Flow

References

CHAPTER 4 PHYSICAL PROPERTIES OF SEDIMENT

4.1 Size of Sediment Particles

4.2 Shape Factor of Sediment Particles

4.3 Fall Velocity

4.4 Angle of Repose for Sediments

References

CHAPTER 5 SCOUR CRITERIA AND SCOUR‑RELATED PROBLEMS

5.1 Critical Shear

5.2 Shields Diagram

5.3 Other Scour Criteria Based on Shear Stress

5.4 Critical Shear on Side Slopes

5.5 Permissible Velocity

5.6 Distribution of Boundary Shear in Trapezoidal Channels

5.7 Boundary Shear in Bends

5.8 Design of Stable Channels Subject to Scour but not to Silt

5.9 Local Scour Around Bridge Piers

5.10 Local Scour Around Embankments

References

CHAPTER 6 ALLUVIAL BED FORMS AND FLOW RESISTANCE

6.1 Bed Forms

6.2 Prediction of Bed Forms

6.3 Bed Form Dimensions

6.4 Effect of Water Temperature

6.5 Stage-Discharge Predictors for Alluvial Channels

References

CHAPTER 7 SEDIMENT MOVEMENT IN RIVERS

7.1 Bed Load Formulas

7.2 Turbulent Diffusion and Diffusion Equation

7.3 Suspended Sediment Discharge

7.4 Bed Material Load Formulas

7.5 Evaluation of Formulas

7.6 Effect of Water Temperature

7.7 Effect of Suspended Sediment on Flow Characteristics

7.8 Sediment Transport in Nonuniform Flow

7.9 Sediment Sorting

7.10 Sampling Fluvial Sediment

References

CHAPTER 8 FLOW IN CURVED RIVER CHANNELS

8.1 Basic Equations

8.2 Transverse Velocity Profiles for Fully Developed Flow

8.3 Boundary Shear Stress

8.4 Transverse Bed Slope and Grain‑Size Distribution

8.5 Lateral Bed‑Load Transport

8.6 Energy Expenditure in Curved Open Channels

8.7 Streamwise Variation of Spiral Motion

8.8 Computation of Flow through Curved Channels

8.9 Transverse Flow and Cross-Stream Flow in River Channels

References

PART III REGIME RIVERS AND RESPONSES

CHAPTER 9 ANALYTICAL BASIS FOR HYDRAULIC GEOMETRY

9.1 Applicable Physical Relationships

9.2 Physical Relationships Pertaining to Stable Width

CHAPTER 10 DESIGN OF STABLE ALLUVIAL CHANNELS

10.1 Regime Methods for Stable Alluvial Canal Design

10.2 Rational method for Stable Alluvial Canal Design

10.3 Design of Stable Alluvial Canals in a System

10.4 Maturing of Canals

10.5 Hydraulic Geometry of Gravel‑Bed Streams

CHAPTER 11 ANALYTICAL RIVER MORPHOLOGY

11.1 Analysis of River Meanders

11.2 Power Approach to River Morphology and Thresholds

11.3 Channel Geometry, Channel Patterns and Thresholds

11.4 River Channel Changes: Adjustments of Equilibrium

11.5 Formation of Alternate Bars

CHAPTER 12 PLAN GEOMETRY AND PROCESSES OF RIVER MEANDERS

12.1 Sine‑Generated Curve

12.2 Meander Path Based on Streamwise Variation of Helical Motion

12.3 Processes Governing Meander Bend Migration

12.4 On the Cause of River Meandering

References for Part III

PART IV MODELING OF RIVER CHANNEL CHANGES

CHAPTER 13 MATHEMATICAL MODEL FOR ERODIBLE CHANNELS

13.1 Physical Foundation of Fluvial Process-Response

13.2 Channel Width Adjustments during Scour and Fill

13.3 Analytical Basis of the FLUVIAL Model

13.4 Water Routing

13.5 Sediment Routing

13.6 Simulation of Changes in Channel Width

13.7 Simulation of Changes in Channel Bed Profile

13.8 Simulation of Changes Due to Curvature Effect

13.9 Test and Calibration of Mathematical Model

CHAPTER 14 COMPUTER-AIDED STUDY OF ALLUVIAL RIVERS

14.1 General Scour at Bridge Crossings

14.2 Gradual Breach Morphology

14.3 Stream Channel Changes Induced by Sand and Gravel Mining

14.4 Tidal Responses of River and Delta System

14.5 Water and Sediment Routing Through a Curved Channel

14.6 Fluvial Design of River Bank Protection

14.7 Stream Gaging of Fluvial Sediment

References for Part IV

PART V RIVER ENGINEERING

CHAPTER 15 RIVER TRAINING

15.1 Bank Protection

15.2 Dikes

15.3 Grade Control Structures

References

APPENDIX: SOME COMMONLY USED TABLES

NAME INDEX

SUBJECT INDEX

Return To Howard H. Chang Home Page