Groundwater is a basic resource for humans and natural ecosystems and is one of the nation's most important natural resources. Groundwater is pumped from wells to supply drinking water to about 130 million U.S. residents and is used in all 50 states. About 40 percent of the nation's public water supply and much of the water used for irrigation is provided by groundwater. Despite the importance of groundwater as one of our most precious natural resources, an organized, effective program to provide an ongoing assessment of the nation's groundwater resources does not exist. With encouragement from the U.S. Congress, the USGS is planning for a new program of regional and national scale assessment of U.S. groundwater resources, thus helping bring new order to its various groundwater resources-related activities. The Survey's senior scientists requested advice in regard to the design of such a program. In response, the committee undertook this study in support of developing an improved program relevant to regional and national assessment of groundwater resources. This report is a product of the Committee on USGS Water Resources Research, which provides consensus advice on scientific, research, and programmatic issues to the Water Resources Division (WRD) of the U.S. Geological Survey (USGS). The committee is one of the groups that work under the auspices of the Water Science and Technology Board of the National Research Council (NRC). The committee considers a variety of topics that are important scientifically and programmatically to the USGS and the nation, and it issues reports when appropriate. This report concerns the work of the WRD in science and technology relevant to assessments of groundwater resources on regional and national scales. The USGS has been conducting scientific activity relevant to groundwater resources for over 100 years and, as summarized in Appendix A, today groundwater-related work occurs throughout the WRD.

Due to its height, density, and thickness of crown canopy; fluffy forest floor; large root system; and horizontal distribution; forest is the most distinguished type of vegetation on the earth. In the U.S., forests occupy about 30 percent of the total territory. Yet this 30 percent of land area produces about 60 percent of total surface runoff, the major water resource area of the country. Any human activity in forested areas will inevitably disturb forest floors and destroy forest canopies, consequently affecting the quantity, quality, and timing of water resources. Thoroughly updated and expanded, Forest Hydrology: An Introduction to Water and Forests, Third Edition discusses the concepts, principles, and processes of forest and forest activity impacts on the occurrence, distribution, and circulation of water and the aquatic environment. Brings water resources and forest-water relations into a single, comprehensive textbook Focuses on the concepts, processes, and general principles in forest hydrology Covers functions, properties, and science of water; water distribution; forests and precipitation, vaporization, stream flow, and stream sediment Discusses watershed management planning and practical applications of forest hydrology in resource management In a single textbook, Forest Hydrology: An Introduction to Water and Forests, Third Edition comprehensively covers water and water resources issues, forest characteristics relevant to the environment, forest impacts in the hydrological cycle, watershed research, watershed management planning, and hydrologic measurements. With the addition of new chapters, new issues, and appendices, this new edition is a valuable resource for upper-level undergraduates in forest hydrology courses as well as professionals involved in water resources management and decision-making in forested watersheds.