Water and the Forest Service

USDA Forest Service
Policy Analysis
P.O. Box 96090
Washington , DC 20090-6090

Public concern about adequate supplies of clean water led to the establishment in 1891 of federally protected forest reserves. The Forest Service Natural Resources Agenda is refocusing the agency on its original purpose. This report focuses on the role of forests in water supply—including quantity, quality, timing of release, flood reductions and low flow augmentation, economic value of water from national forest lands, and economic benefits of tree cover for stormwater reduction in urban areas.


Forests are key to clean water. About 80 percent of the Nation's scarce freshwater resources originate on forests, which cover about one-third of the Nation's land area. The forested land absorbs rain, refills underground aquifers, cools and cleanses water, slows storm runoff, reduces flooding, sustains watershed stability and resilience, and provides critical habitat for fish and wildlife. In addition to these ecological services, forests provide abundant water-based recreation and other benefits that improve the quality of life.


Use and development of the water resources of the United States underwent major changes during the 19th century in response to the growing demands of a population that had increased nearly 20-fold since the founding of the country. Westward expansion, and navigable rivers, canals, and harbors for transportation transformed the Nation's economy. As the Nation experienced this period of massive development, major problems emerged from overuse and poor management of its water resources:

  • Urban water supplies were a major source of disease.
  • The capacity of many lakes and streams to assimilate wastes was exceeded.
  • The survival of people living in arid or flood-prone areas depended on unpredictable precipitation patterns.

The 1897 Organic Administrative Act said these forest reserves were to protect and enhance water supplies, reduce flooding, secure favorable conditions of water flow, protect the forest from fires and depredations, and provide a continuous supply of timber.

By 1915, national forests in the West had been established in much the form they retain today. These national forests, which included 162 million acres in 1915, were essentially carved out of the public domain. At that time, few Federal forests were designated in the East because of the lack of public domain. Public demands for eastern national forests resulted in passage of the 1911 Weeks Act, authorizing the acquisition of Federal lands to protect the watersheds of navigable streams. From 1911 to 1945, about 24 million acres of depleted farmsteads, stumpfields, and burned woodlands were incorporated into the eastern part of the National Forest System.

This report focuses on the role of forests in water supply—including quantity, quality, timing of release, flood reductions and low flow augmentation, economic value of water from national forest lands, and economic benefits of tree cover for stormwater reduction in urban areas.


Throughout human history, water has played a central, defining role. It has sculpted the biological and physical landscape through erosion and disturbance. The amount, place, and timing of water are reflected in the vegetative mosaic across the landscape. Water has also played a key role in shaping the pattern and type of human occupancy; routes of travel and transportation, patterns of settlement, and the nature and scope of human land-use all owe their characteristics largely to water regimes.

Conversely, social demands on the water resource system have produced major effects on virtually every aspect of that system including quality, quantity, distribution, and form (for example, white water vs. impoundments).

The human uses and values of water shape how it is managed, and the biological and physical characteristics of water shape human values and uses. Thus, water resource management requires systems approach that includes not only all of the constituent parts, but also the links, relations, interactions, consequences, and implications among these parts.

Traditionally, water has been valued as an engine of development and as the source of commodity and utilitarian values to society. It has sustained agricultural production, grown forests, and powered cities and industries. Today, these values remain, but they have been joined by a variety of others. Water is the basis for many of the recreational and amenity values people seek. Increasingly, science shows, and managers recognize, the key role of water flow regimes in ecosystem function and processes. Adequate flow and water quality are essential to maintaining key fish species and fisheries, which in turn, are sources of many economic, cultural, and spiritual values.

Across the Nation, significant challenges to resource managers, scientists, and citizens are presented by emerging conflicts over providing high quality, abundant flows of water to sustain a burgeoning population, an agricultural industry, historic salmon runs, and populations of other threatened aquatic species.


How Much Water Comes from the National Forests?

Excluding Alaska , about two-thirds of the Nation's runoff comes from forested areas. National forest lands contribute 14 percent of the total runoff. National forest lands are the largest single source of water in the United States and contribute water of high quality. More than 60 percent of the Nation's runoff is from east of the Mississippi River , where 70 percent of the Nation's private and State forests are located. National forests in the East are responsible for 6 percent of this runoff. National forests in the West provide proportionately more water (33 percent) because they include the headwaters of major rivers and forested areas of major mountain ranges. Forest Service literature from the 1940's to the present has claimed that 50 to 70 percent of the Nation's runoff comes from national forest lands. It is now clear that those claims are overstated.

What is the Value of Water from National Forest Lands?

We calculate the marginal value of water from all national forest lands to equal at least $3.7 billion per year. Annual value of water from national forest lands is greatest in the Pacific Northwest and Pacific Southwest Regions, and lowest in the Southwest Region.
These values represent a lower limit on the range of values attributable to waters flowing from the national forests. The actual values of this water yield are almost certainly higher, but how much higher is not known.

How Should Municipal Watersheds be Managed?

One issue is whether municipal watersheds should be placed under active or passive management regimes to sustain supplies of high-quality water over the long run. Many Forest Service specialists think that water supplies can be best protected by actively managing these watersheds to maintain forest vegetation and watershed processes within their natural range of variation. Conversely, many people in urban centers believe that, in the interest of water quality and safety, people should not alter watersheds in any way, other than to divert the water. Scientific evidence indicates that watersheds can be effectively managed for safe, high-quality water and still provide other resource outputs as byproducts.

Can Forests be Managed to Improve Stream Flow?

Flooding and sedimentation from cutover lands was one of the primary reasons for establishing national forests. The timing of water yields was also an important issue, especially the desire to augment late-season flows.

Vegetative cover and on-site control measures effectively reduce flood peaks. However, significant shifts in the timing of late-season runoff are not likely to be achieved through managing forest vegetation and snow across national forest lands. Treatments that restore slopes, meadows, and channels; increase the routing time between precipitation and runoff; and recharge ground waters can be expected to have a greater effect in sustaining late-season flows.

Although theory suggests that vegetation management can produce more streamflow, for a variety of reasons, general water-yield increases through forest management are likely to fall in an undetectable range. The data suggest that relying on augmentation from national forests will not be a viable strategy for dealing with water shortages. Greater gains can be made by reducing water consumption, improving conservation, and establishing water markets to allocate scarce supplies more efficiently. Providing cold, clear waters of high quality for aquatic organisms and human use is probably the proper focus for managing water on the National Forest System. There is relatively little management can do to increase total water yield, but forest management can have major effects on water quality—affecting temperature, nutrient loadings, sediment yields, and toxic contaminants.

What is the Agency's Role in Protecting Instream Flow and Ground Water?

The Forest Service must actively participate in the processes that allocate surface water, ground water, and water rights. To be effective, this participation must be timely and of impeccable technical quality.

Three needs stand out:

Forest plan revisions should incorporate instream flow needs to maintain public values. When a State undertakes a basin-wide adjudication of water rights, all beneficial consumptive and instream water uses on national forest lands should be claimed in accordance with State and Federal laws.

Early and intensive collaboration among existing and potential water users is likely to be the most effective approach. Public and interagency collaboration in forest planning has great potential for solving problems and achieving acceptable solutions, lessening the costly litigation common to water rights issues.

In many places, the Forest Service lacks the technical expertise in hydrology needed to protect instream flows. Our present workforce of in-house expertise must be conserved and enhanced if costly failures are to be avoided.

Can the Watershed Condition on National Forests be Restored?

The most comprehensive landscape-scale assessment to date—the Interior Columbia Basin Assessment— found that the momentum from past events will push the system further from the desired condition over the decades to come. Even with aggressive management, that momentum will not be overcome within the next 100 years under projected funding. Progress toward forest health restoration can be expected to proceed very slowly. In the interim, vegetative composition and structure at the landscape scale will be determined by unnaturally large, high-intensity fires.

These findings suggest that it will not be feasible torestore all degraded areas. We will have to strategically focus restoration efforts on selected watersheds where we can hope to make a meaningful difference.

What is the Role of Urban Forests in Water Supply?

Counties classified as “urban” contain one-quarter of the total tree cover of the coterminous United States . Urban trees affect water quantity by intercepting precipitation, increasing water infiltration rates, and transpiring water. They can materially reduce the rate and volume of storm water runoff, flood damage, stormwater treatment costs, and other problems related to water quality.

The Agency Challenge.

The challenge for the Forest Service will be to simultaneously perform the following:

  • Systematically restore damaged watersheds on the national forests.
  • Mitigate additional watershed damage from land uses and the inevitable major wildfires.
  • Foster partnership efforts to meet the most pressing watershed restoration needs when they fall outside of national forest boundaries.