Fuels Planning: Science Synthesis and

Integration

Environmental Consequences Fact Sheet: 8

Evaluating Sedimentation Risks

Associated With Fuel Management

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-23-8-WWW

March 2005

Fuels planning: Science synthesis and integration, an interagency research/management

partnership to support the Ten-Year Fire Plan,

led by Russell T. Graham, RMRS, and Sarah M.

McCaffrey, NCRS.

Synthesizing

Scientific Information

for Fire and Fuels

Project Managers

Environmental Consequences

Team Leader

Elaine Kennedy Sutherland

USDA Forest Service

Rocky Mountain Research Station

Missoula, MT

William Elliot

Pete Robichaud

USDA Forest Service

Rocky MountainResearch Station

 Moscow, ID

Erosion Rates in Forested Watersheds

This fact sheet describes the sources of sediment in upland forest watersheds in

the context of fuel management activities. It presents the dominant forest soil

erosion processes, and the principles behind a new sediment delivery interface

developed to aid in erosion analysis of fuel management projects.

Removing sediment collected from a single storm on a 5-ha

watershed following a wildfire in Colorado

Undisturbed forested watersheds have little erosion. Natural forests, however, have a

natural cycle of disturbances

that include wildfire and large

flood events. The fire return interval, or the return period of

flood events, ranges from decades to centuries. When either

of these events occurs, there will

be large upland erosion. This

leads to considerable sediment

deposition and movement within

forest streams. Long-term natural background sediment yields from watersheds are a combination of the low

levels of erosion from undisturbed forests plus the added erosion from occasional disturbances.

Human activities such as thinning, prescribed fire, and roads generally cause

some level of disturbance. Erosion rates associated with these activities are generally lower than rates from wildfire or flooding but may occur more frequently.

For example, roads near streams are a source of annual erosion. Table 1 lists

some observed erosion rates from a number of research studies carried out in

recent years.

The upland erosion rates in table 1 may take a number of years, or even decades,

to be routed through a forest stream system. In dry years, little sediment will be

Table 1—Typical measured upland erosion rates and length of time between disturbances.

Disturbance Erosion rate Time between disturbances

Mg/ha years

Wildfire 0.03–10.4 (average 6.0) 20–300

Prescribed fire 0.0–0.09 (average 0.02) 2–80

Thinning or logging 0.0–0.2 (average 0.1) 20–150

Road segments 0.13–10.2 (average 5.2) Annual

Pacific Northwest

Research Station

Rocky Mountain

Research Station
The Fuels Planning fact sheets are based on preliminary findings. Information from fact sheets will be synthesized in an upcoming publication.

Environmental Consequences Fact

Sheets

Look for fact sheet topics from the Environmental Consequences

Team including information about the effects of fire behavior and

alternative treatment strategies, Wildlife Response Model, weed responses, riparian systems, soil erosion, restoration objectives, treated

spaces, the Fire Effects Information System (FEIS), and the First

Order Fire Effects Model (FOFEM).

Fuels Planning: Synthesis and Integration

This fact sheet is one in a series being produced as part of a larger

project supported by the USDA Forest Service to synthesize new

knowledge and information relevant to fire and fuels management.

Fact sheets address topics related to stand structure, environmental

impacts, economics, and human responses to these factors. Information in the fact sheets is targeted for the dry forests of the Inland

West, but is often applicable across broad regions of the country.

For more information, please visit our Web site at:

www.fs.fed.us/fire/tech_transfer/synthesis/synthesis_index

routed. In wetter years, considerable amounts of sediment may be delivered to, routed through, and delivered from forest streams.

Calculating Long-Term Effects

The values in table 1 can be used to compare long-term

average annual effects of disturbances by dividing the

sediment delivered from the disturbance by the time between disturbances. The fraction of the watershed in

roads also has to be determined to complete the analysis.

Table 2 gives an example of such calculations. The

amount of roads in a watershed can often be expressed

as total kilometers of road per square kilometer of watershed, or a percent of the surface of the watershed. A

typical value is around 2.5 percent. Times between disturbances that are typical of the Northern Rocky Mountains are also given in table 2. The variables in the table

depend on soil properties, topography, disturbance, and

climate. Sediment delivery rates may also be lower if

improved practices—such as minimizing onsite disturbance, optimizing timing of activities, or using buffers—

are used.

A Tool for Planners and Managers

The tool WEPP Fuel Management interface (WEPP:

FuMe) specifically aids in predicting sediment delivery

values as given in table 2. It is online at http://forest.

moscowfsl.wsu.edu/fuels/

Selected References

Covert, S. A.; Robichaud, P. R.; Elliot, W. J.; Link, T. E.

[In review]. Accuracy assessment of WEPP-based erosion models for harvested and burned forest watersheds.

Moscow, ID: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station.

Foltz, R. B. 1996. Traffic and no-traffic on an aggregate

surfaced road: sediment production differences. In: Proceedings of the seminar on environmentally sound forest roads and wood transport; 1996 June 17–22; Sinaia,

Romania. Rome: FAO: 195–204.

Luce, C. H.; Black, T. A. 2001. Spatial and temporal patterns in erosion from forest roads. In: Wigmosta, M. A.;

Burges, S. J., eds. Influence of urban and forest land

uses on the hydrologic-geomorphic responses of watersheds. Water Resources Monographs. Washington, DC:

American Geophysical Union: 165–178.

MacDonald, G. I.; Harvey, A. E.; Tonn, J. R. 1999. Fire,

competition and forest pests: landscape treatment to

sustain ecosystem function. In: Neuenschwander, L. F.;

Ryan, K. C., eds. The joint fire science conference and

workshop; 1999 June 15–17; Boise, ID. [Online]. http:/

/www.nifc.gov/joint_fire_sci/conferenceproc/ [January

2005].

Table 2—Calculations of long-term average annual effects of

disturbances.

Average

Time annual

Erosion between sediment

 Disturbance rate disturbances delivery

Mg/ha years Mg/ha

Wildfire 6.0 40 0.15

Prescribed fire 0.02 20 0.001

Thinning or logging 0.10 20 0.005

Road segments

 (assuming 2.5%

 of watershed) 0.125 1 0.125