The physical basis of water flow in saturated and unsaturated soils has been established in this century, and applications in hydrology, geology, civil engineering, and related environmental sciences are spreading rapidly. The purpose of this book is to convey a better understanding of water flow in soils through clear and essentially nonmathematical explantations. Each chapter introduces substantial topics on soil water flow, providing both phenomenological and analytical interpretations. Chapter 1 serves as an introduction and describes how the state of water in soil is defined. The fundamental concept of water flow in uniform soils is explained in Chapter 2. Infiltration theories are reviewed and the classic Green-Ampt theory as well as Philip's theory are reevaluated. In Chapter 3, refractional water flow in soils is described. In this chapter, as well as in the following chapters, water flows are well illustrated to help the readers understand the phenomenon. Preferential flows of water such as the bypassing flow, funnel flow, and fingering flow are discussed in Chapter 4. In Chapter 5, physically based hill slope hydrology is explained. Chapter 6 discusses the effects of temperature gradients in soils and clarifies the peculiarity of thermally induced water flow. The effects of microbiology on water flow in soils are explained in Chapter 7. Water regime in fields with vegetation is explained in Chapter 8: water flow through the soil and plant roots system is discussed synthetically and the water regimes for different varieties of vegetation are exemplified. Finally, in Chapter 9, spatial variability and field heterogeneity of soil physical properties are discussed and the literature on each topic is reviewed. Water Fow in Soils does not devote many pages to mathematical models and their solutions. Instead, this book provides descriptions of phenomenta, with abundant illustrations of water flow in soils. The existing texts on soil physics are sometimes too difficult for readers who do not have a basic knowledge of physics, mathematics, or soil science. This book provides a phenomenological approach with simple and logical explantations on water movement in soils. Although the concepts of water flow have been examined in soil physics, they have generally not been expanded to include environmental sciences. And whereas hydrology has offered a lot of mathematical models for the formulation of soil water processes, the physical descriptions of the processes have not necessarily been sufficient. This book bridges the fields of soil physics (where descriptions of water flow tend to be microscopic) and hydrology (where they tend to be macroscopic). This new field can be called soil-hydrology.
