Introduction to Hydrology

Water scientists and engineers of tomorrow must be equipped to deal with a diversity of issues such as the design and operation of data retrieval and storage systems; forecasting; developing alternative water use futures; estimating water requirements for natural systems; exploring the impacts of climate change; developing more efficient systems for applying water in all water-using sectors; and analyzing and designing water management systems incorporating technical, economic, environmental, social, legal, and political elements. A knowledge of hydrologic principles is a requisite for dealing with such issues.

In the early years of the twentieth century, water resources development and management were focused almost exclusively on water supply and flood control. Today, these issues are still important, but environmental protection, ensuring safe drinking water, and providing aesthetic and recreational experiences compete equally for attention and funds. Furthermore, an environmentally conscious public is pressing for greater reliance on improved management practices, with fewer structural components, to solve the nation's water problems. The notion of continually striving to provide more beater has been replaced by one of husbanding this precious natural resource.

There is a growing constituency for allocating water for the benefit of fishand wildlife, for protection of marshes and estuary areas, and for other natural system uses. But estimating the quantities of water needed for environmental protection and for maintaining and/or restoring natural systems is difficult. Scientific data are sparse, and our understanding of the complex interactions inherent in ecosystems of all scales is rudimentary. And this is a critical issue, since the quantities of water involved in environmental protection can be substantial, and competition for these waters from traditional water users is keen. The nations of the world. are facing major decisions regarding natural systems, decisions that are laden with significant economic and social impacts. Thus there is an urgency associated with developing a better understanding of ecologic systems and of their hydrologic components.

The fifth edition has been rewritten to acquaint future water scientists and managers with the basic elements of the hydrologic cycle. It reviews data sources, introduces statistical analyses in the context of hydrologic problem-solving, covers the components of the hydrologic budget, discusses hydrograph analysis and routing, and introduces groundwater hydrology, urban hydrology, hydrologic models, and hydrologic design. The book is designed to meet the needs of students who expect to become involved in programs that are concerned with the development, management, and protection of water resources. Many solved examples and problems serve to amplify the concepts presented in the text. Many appropriate Internet addresses are provided.

Numerous sources have been drawn upon to provide subject matter for the book, and the authors hope that suitable acknowledgment has been given to them. The authors also thank the following reviewers: Istvan Bogardi, Meteoroligia, Hungary; Praveen Kumar, University of Illinois; David B. Thompson, University of Texas; and Jose D. Salas, Colorado State University. Colleagues and students are also recognized for their helpful comments and reviews.

WARREN VIESSMAN, JR.
GARY L. LEWIS