istrative levels. Watershed management is one method for addressing these needs for integration.
Government and private sponsors gave the National Research Council's Committee on Watershed Management three tasks: investigate the present state of knowledge about watershed management, investigate representative examples of the application of the approach, and identify barriers to successful implementation of such approaches and means for overcoming them. The committee pursued its work based on the idea that watersheds of all sizes, ranging from small local drainages to large river basins, were part of the charge. The committee's activities included much research as well as efforts to talk to people involved in watershed initiatives at all levels, from large, regional planning approaches to small, local projects. We held meetings or workshops in Washington, D.C.; Tennessee; California; and Minnesota; and met in total five times over our two-year study to deliberate and write this report. The committee hopes this effort will be of value to a wide range of potential users, including watershed managers from local to national levels, researchers, Congress,' and the executive agencies of the federal government.
Watersheds are defined by the "waterscape," the combination of the hydrology and topography of the landscape, and they are ubiquitous units that can be seen as the physical foundation of the nation. The U.S. Geological Survey provides a standardized definition of regions and watersheds that subdivides the nation into hydrologic units averaging about 700 square miles. These units provide a common basis of discussion for the public, planners, decisionmakers, and scientists who deal with water-related issues. Although social and economic data are not collected with respect to these natural boundaries, modem geographic information systems allow reformulating of diverse data sets into common frameworks. This tool increasingly allows managers to use ecological, social, and economic data in concert.
The environmental, social, and economic diversity of the United States dictates that one standard solution is unlikely to be useful in all parts of the country. A huge range of environments occurs between the humid east coast and the progressively dry mid-continent area, between the well-watered Pacific northwest and the arid southwest. Population densities range from the crowded northeast to the sparsely settled intermountain regions. Regional variations in wealth are substantial. Any well-designed national policy for watershed management must maintain great flexibility to accommodate these natural and human variations and allow significant local control and input to decisions.
Governmental attempts at watershed management have been ongoing in the United States for more than half a century, but the science of watershed management is still evolving and many of our current activities are, in essence, experi-