Hydraulics of Stepped Chutes and Spillways

1R37. Hydraulics of Stepped Chutes and Spillways. - H Chanson (Dept of Civil Eng, Univ of Queensland, Brisbane, Australia). Balkema Publ, Rotterdam, Netherlands. 2002. 384 pp. ISBN 90-5809-352-2. 105. 00. Reviewed by AS Paintal (Eng Dept, Metropolitan Water Reclamation District, 100 E Erie St, Chicago IL 60611). This book provides a comprehensive coverage of most of the engineering topics in the hydraulic design of stepped chutes and spillways. The stepped channels and chutes have been in use for more than 3500 years, but there is no publication on the hydraulic design of these structures. Since 1980s, there has been a renewed interest in these structures for water and wastewater treatment plants and flood control facilities due to development of new construction techniques and materials. This book fulfills the need for presenting the state of the art in the stepped chute hydraulics. It helps students as well as practicing engineers and researchers get a feel for various aspects of the stepped chute hydraulics. The book is organized in ten chapters and nine appendices. The chapters provide an orderly development of the subject. Chapter 1 gives a brief introduction of the subject and discusses the organization of the book. A stepped chute is defined as a channel with a series of drops in the channel bed. The flow in this channel is classified based upon the geometry of steps and flow rate. Three regimes of flow are defined, they are: nappe flow regime at low flow rates, transition flow regime at intermediate flow rate, and skimming flow regime at large flow rates. Chapter 2 provides a brief history on the development of the design and construction methods and materials for stepped chutes and spillways. The stepped cascades have been in use for aqueducts and fountains since historic times. Chapter 3 deals with the hydraulics of nappe flow regime. The nappe flow is defined as a succession of free falling sheets of water with the jet impinging on the next lower step. On the lower step, either the flow is supercritical, or a full or partial hydraulic jump is formed. The energy is lost in impact and in hydraulic jump. Chapter 4 is concerned with transition flow regime that is defined as transition from nappe flow regime to skimming flow regime. This regime is associated with the severe hydrodynamic fluctuations and is, therefore, avoided in the design. Chapter 5 discusses the skimming flow regime, in which the flow skims over the steps with the external edges of the steps forming a virtual-channel bed. The energy is dissipated due to vortices that are formed in each corner. As the dissolved oxygen concentration is a prime indicator of the quality of water, Chapter 6 discusses the aeration and de-aeration characteristics of cascading water. The cascades are very efficient means of aeration due to turbulent mixing and air entrainment. In Chapter 7, new design methods and guidelines are presented for various applications of stepped chutes. The design procedures for stepped spillways, stepped channels at the toe of the chute, stepped fountains, and water staircases are discussed in detail with a number of examples. Historic accidents and failures of hydraulic structures with stepped chutes and channels are discussed in Chapter 8. Recommendations are formulated for safe and efficient design. The author recommends avoiding transition flow regime as hydrodynamic fluctuations are inherent in this flow regime. Quality of construction methods and materials, and good maintenance practices are also emphasized. Chapter 9 deals with the flow instabilities and unsteady wave phenomena that occur in the stepped channels and spillways. Basic theory is provided for the wave phenomena, and the documented experiences are reviewed. Chapter 10 provides a summary and makes recommendations for future research on the air-water gas transfer process in nappe and skimming flow regimes, hydraulic characteristics of transition and skimming flow regimes, and hydrodynamic loads on the steps. There are nine appendices. Appendix 1 gives a list of physical and chemical properties of fluid in SI units, while Appendix 2 provides a table for unit conversions. A method for computing nappe trajectory is given in Appendix 3, and Appendix 4 explains a procedure for computing bubble rise velocity. A method for modeling form drag and resistance to flow is given in Appendix 5, and void fraction distribution in chute flow is discussed in Appendix 6. A method of computing the flow in stepped chute for skimming flow regime is given in Appendix 7, and a procedure for modeling air-water gas transfer in skimming flow regime is presented in Appendix 8. Appendix 9 provides a procedure for reporting errors and omissions in the book. A list of symbols, a comprehensive glossary of technical terms, and a list of references are also included in the book. The hydraulics of stepped chutes differs from the classical hydraulics of smooth channels and is not usually taught in schools. The books on classical hydraulics do not cover this topic either. The purpose of the book has been to provide basic hydraulic theory related to designing stepped chutes and spillways. The book is based on a state-of-the-art-review of literature and research reports. The book is very well illustrated with a large number of charts and photographs. The photographs show hydraulic structures built over the years that incorporate stepped chutes for energy dissipation, flood control, and aesthetics (landscaping). Hydraulics of Stepped Chutes and Spillways is a useful contribution to the field of hydraulics. The book may be used as a text for an undergraduate (elective) or a graduate course in the hydraulics of stepped chutes. The book will be useful for engineers working in the area of design and research.