This book is proposed for use as a text in advanced soil physics or vadose zone hydrology. I hope that it will also prove to be a useful reference for students, researchers, and modelers interested in soil water flow, contaminant transport, and environmental pollution abatement.

The emphasis throughout is on quantitative rather than qualitative descriptions. The basic framework and terminology address flow and transport, but the detailed descriptions are slanted towards mathematical development and analysis. The book presents relevant material for a three-unit, one-semester class. The intent is for the instructor and students to coordinate selected topics from this book with current literature or other activities to customize the course emphasis.

More than 175 practice and discussion questions are presented. Additionally, computer programs are presented, which appear on the accompanying CD along with some of the tabular data presented. Several short MathCad programs have been used to illustrate and/or perform detailed calculations. The reader can reproduce similar results by whatever means are at his/her disposal, such as spreadsheets or high-level programming languages. Additionally, there are a half dozen programs given in FORTRAN, primarily providing solutions to the nonlinear Richards' equation. These programs emphasize both the numerics and the physical results, and are simplified for ease of understanding. There are also examples to illustrate simultaneous water and solute flow using readily-available programs by other authors--these emphasize the problem addressed, with less attention to the numerical aspects.

As a reference, this book develops the basic flow equations and provides solutions and methodology under one cover. Until now, such material has only been available in scattered journals and chapters. A unique feature here is the presence of a number of analytical solutions for variably saturated flow and solute transport. These complement sections on numerical techniques. As mentioned above, there are numerous examples and calculations presented. These can be studied and, in some cases, applied directly.

Noting the differences between this book and some of the excellent works already available may help with an overall perspective. First the presentation is more quantitative than the more basic books by Jury et al. (1991) and Hillel (1998). The same is generally true of the comparison with Marshall et al. (1996), the soil hydrology book by Kutilek and Nielsen (1994), and the vadose zone hydrology book by Stephens (1996). In my opinion, topics presented by Tindall and Kunkel (1999) are broader, and those by Selker et al. (1999) are more detailed than in this book. The style is somewhat more akin to Kirkham and Powers (1972), but with a much stronger emphasis on variably saturated processes and solute transport.

Although recent citations and developments are included, I recognize that several contemporary and important topics have been left out or are mentioned only briefly. For example, there are only limited discussions of preferential flow, spatial variability, and stochastic processes. Promising techniques utilizing fractals and scaling are mentioned only briefly, with nothing said on percolation theory. I also faced a dilemma with respect to numerical methods and the use of available computer programs. I decided to address finite differences (as opposed to also discussing additional techniques) and to give only an overall impression of the third-party programs that were used.

I have made little effort to assure that the "original" reference was cited for many topics. However, it is believed that sufficient references are given to trace back through the literature when necessary or of interest. The tendency here has been to cite work that is the most familiar, such as my own or that by close associates. I sincerely apologize in advance to many of my colleagues, whose key and profound contributions may not be mentioned!

The Sherlock Holmes quotes are strictly for entertainment. These, and more, can be found in Beaman (1980).