Review of Wadi Hydrology by Zekai Sen: CRC Press, Taylor & Francis Group, Boca Raton, Florida; 2008; ISBN: 978-1-4200-6154-3; 347 pp.

 In preface of the book, the author states the purpose of the book is to “[P]rovide a comprehensive presentation of up-to-date models for utilization with arid and semiarid region water resources and their applications. In addition to an overview of fundamentals in the field, readers will find a useful summary of current developments as reported in the world’s leading hydrology journals.” The book is reviewed keeping this objective in mind.

The subject matter of the book is divided into seven chapters. The first chapter is introductory, providing a general overview of arid regions, problems faced by these regions, and factors effecting hydrologic phenomena and processes occurring in these regions. Arid regions are classified, based on precipitation as humid, extremely humid, semiarid, arid, and extremely arid; when temperature is used then they are classified as cold, warm, and hot. Desertification is discussed next. Then follows a discussion of droughts, including different types of droughts, such as meteorological, hydrologic, and agricultural. For better understanding of droughts different events are considered: aridity, drought, water shortage, and desertification. The chapter then goes on to discuss climate change impacts and wadi hydrology, and is concluded with a discussion of methodological distinctions between wadi hydrology and humid region hydrology. The chapter provides a very good overview of wadi hydrology and the issues and problems involved, and sets a context for the chapters to follow. Looking at the references, one notices that one reference is dated 2005, two are dated 2002, and the remainder are at least ten years old.

Chapter 2 deals with wadi characteristics. Providing a general overview, it goes on to discuss geomorphology; soils; land forms, including alluvial fans, alluvial fills, sand dune, delta deposits, coastal and plain deposits, and playas; rock environments; drainage basin features, including drainage areas, stream slope, drainage density, centroid, length, and elevation features; and time of concentration, including the average time of concentration. It is not clear from the discussion if the empirical laws of geomorphology, such as Horton’s and others, will apply to wadi hydrology. Also, the concept of lag time does not figure prominently in the discussion, although it is an important concept in rainfall-runoff hydrograph synthesis. Excepting one reference, all other references in the chapter are at least ten years old.

Rainfall pattern constitutes the subject matter of chapter 3. It discusses rainfall features; temporal distribution of rainfall; aridity index; accumulative rainfall curves; rainfall intensity, including duration, intensity-duration-frequency relationships, and average intensity-duration models; rainy and nonrainy days; rainfall distribution functions and prediction; spatial distribution of rainfall; triple variable drought description; and Jordan climatology. Description of rainfall fields using radar technology is missing. All but five references are ten or more years old.

Chapter 4 deals with runoff hydrograph analysis. Beginning with a discussion of hyetograph-hydrograph relationship, it sets out to discuss rating curves, provide a critique of conventional methods, and discuss infinitesimal runoff coefficient, hydrograph and unit hydrograph derivations, modified Snyder’s synthetic unit hydrograph method, dimensionless unit hydrograph, flood estimation in ungaged basins, cross-section flood discharge, curve number and Manning’s coefficient, and flood hazards. Except for a few references the cited literature is at least ten years old. More important, some very important works on hydrologic systems and more particularly rainfall-runoff systems and modeling are not cited. One glaring omission is Sherman’s work on the origin of unit hydrograph.

Groundwater recharge and evaluation is treated in chapter 5. The treatment includes geology and groundwater, groundwater and recharge, techniques for groundwater estimation, chloride mass balance methods, environmental isotopes, cone of depression, discharge calculations in large diameter wells, aquifer tests, aquifer heterogeneity and methods, type-straight line methods, standard ion method for groundwater quality evaluation, and climate change and groundwater. A vast majority of references are at least ten years old. Classical papers by Chow, Jacob, and others are not cited.

The focus of chapter 6 is groundwater management methods for arid regions. It starts with a treatment of safe yield and groundwater management, management environments in arid regions, arid regions and wadi conditions, strategic groundwater storage planning, probabilistic risk management in an aquifer, groundwater management and well optimization in arid regions, wadi groundwater management system principles, and integrated management principles. The chapter concludes with a discussion of artificial mixing of potable and saline groundwater. Except for one reference, all others are at least ten years old.

The last chapter is on sediment transport in arid regions. It deals with surface cover conditions, sedimentation in arid environments, rock weatherability, soil erodibility, soil erosion conditions, sediment yield modeling in arid regions, and concludes with a formulation of simple sediment yield models. Like other chapters, the literature cited is quite old.

The book is well written, topics are well organized, the prose is easy to read and understand, the style is lucid, and there is a wealth of information reflecting the knowledge and experience of the author. When reading the book, one cannot help but notice the imprint of the author’s own work. It would have been desirable if the book had examples illustrating concepts discussed in each chapter and had a number of end-of-chapter problems. These limitations would inhibit adoption of the book as a textbook. One cannot help but wonder why the literature cited is predominately not current. Is it because not much work has been done in this area in the past ten years or so? Although the book is a good treatment of wadi hydrology, it would have been desirable to have a discussion of newly emerging techniques, such as artificial neural networks, fuzzy logic, data mining, database management systems, intelligent techniques, knowledge-based systems, geographical information systems, digital elevation models, uncertainty analysis, and multivariate stochastic analysis, among others. The emphasis in the book is on surface water, although groundwater is treated in two chapters. However, not much is presented on vadose zone water. Likewise, water quality receives only marginal treatment. Impact of land-use change also receives a perfunctory treatment. Nevertheless, it is recommended as a good reference book and the reader will benefit by reading it. Senior undergraduate students or beginning graduate students in civil and agricultural engineering, earth sciences, or environmental sciences as well as policy and decision makers in the water sector will find the book useful and enlightening.