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Geomorphology and Sediment Transport

Hydrologic and Erosion Responses of Burned Watersheds


Selected Publications 

 

Project Staff

John Moody
U.S. Geological Survey
3215 Marine Street, Suite E-127
Boulder, CO 80303-1066
Telephone: 303-541-3011
Fax: 303-447-2505
email John A. Moody
Deborah A. Martin
U.S. Geological Survey
3215 Marine Street, Suite E-127
Boulder, CO 80303
Telephone: 303-541-3024
Fax: 303-447-2505
email Deborah A. Martin

 

 

Scientific Questions

The enhanced probability of catastrophic wildfires in the western United States and elsewhere in the world has increased the need to understand the flooding risk and the erosion and depositional responses of burned watersheds. In addition, surface water flowing from burned areas may carry increased levels of sediment, organic debris, and chemicals that may contribute to significant degradation of municipal water supplies and aquatic habitats. Our project has three main thrusts: (1) we are investigating the relation between rainfall intensity and peak water discharge from burned watersheds, a relation that depends on the size of the rainstorm, the size of the burned area and burn severity, and the changes in infiltration capacity of the soil; (2) we are investigating the hillslope and channel erosion and deposition processes after wildfire with a focus on predicting these processes on a watershed or landscape scale rather than on a single hillslope plot or channel cross-section scale; and (3) we are examining the water quality impacts of wildfire and are synthesizing post-fire water-quality sampling protocols.

 

After the Buffalo Creek Fire in May 1996, a 100-year rainstorm caused upstream erosion and the subsequent deposition of this alluvial fan at the mouth of a tributary to Buffalo Creek in Colorado. Alluvial Fan. The Buffalo Creek Fire in May 1996 burned 4,690 hectares in the mountains southwest of Denver, Colorado.  This wildfire lowered the erosion threshold of the watershed.  As a consequence of this wildfire, a 100-year rainstorm in July 1996 caused erosion upstream and deposition of this alluvial fan at the mouth of a tributary to Buffalo Creek.  Buffalo Creek is flowing to the right at the bottom of the photograph.  Photo by R. H. Meade

 

Mission or Goal

An extensive body of literature exists on the effects of wildfire on watersheds. Wildfires have burned across the landscape of the western United States for centuries, but the magnitude of the geomorphic effect on the landscape is unknown. By understanding the magnitude of the runoff response and the erosion and deposition responses of recent wildfires, we can provide data for landscape evolution models in areas prone to wildfire. In addition, an understanding of the runoff response will contribute to better methods of predicting post-fire flooding to minimize the loss of life and property. Watershed-scale predictions of erosion and deposition from these natural disasters can be used by land managers to prioritize forest treatments based on erosion potential before and after wildfires. Moreover, we hope to contribute to an understanding of wildfire as an element of an ecosystemís disturbance regime.

 

 

A consequence of wildfire is the increased probability of flash floods such as this one on Spring Creek that occurred in 1997 within the area burned in the Buffalo Creek Fire of 1996. A consequence of wildfire is the increased probability of flash floods.  This flash flood occurred in Spring Creek on 29 July 1997 within the area burned by the Buffalo Creek Fire.  The view  is upstream and the discharge is about 5.0 m3/s from a maximum 30-minute rainfall  intensity of about 19 mm/h.  Rainfall-runoff relations suggest a rainfall threshold at about 10 mm/h above which much larger flash floods occur. Photo by John A. Moody  

 

Another consequence of wildfires and subsequent rainfall is erosion.  This erosion of a drainage created an incised channel after the Cerro Grande Fire near Los Alamos, NM.  The view is upstream and the blue backpack is about 1 meter tall.  The maximum 30-minute rainfall intensity was about 20 mm/h.  The incision seen in this photo was after the wildfire and rain storm; prior to the storm this drainage had no definite banks.  Photo by John A. Moody Rainfall erosion created this incised channel after the Cerro Grande Fire near Los Alamos, New Mexico.

 

Flash floods scar trees by peeling off the bark and subsequently leave clear evidence of the flood's high water mark. Channels draining burned areas have zones of erosion and zones of deposition. This deposition was downstream from an erosion zone shown in the previous photo.  The peeled bark indicates the highest level of water and debris during a flash flood. Sediment is coarse sand and gravel. The view is downstream and the blue backpack is about 1 meter tall.  Photo by John A. Moody  

 

Flooding caused organic debris from Buffalo Creek and Spring Creek to wash into Strontia Springs Reservoir, which supplies drinking water to Denver and Aurora, Colorado, and produced an increase in the level of manganese in the water supply. Strontia Springs Dam
Organic debris and sediment were deposited in Strontia Springs Reservoir, which supplies drinking water to the cities of Denver and Aurora.  This debris came from two watersheds (Buffalo Creek and Spring Creek) burned by the 1996 Buffalo Creek Fire.  Associated with this debris was an increase in manganese, which increased the chlorine demand of water treated for municipal usage.  Photo by John A. Moody
Rill erosion on a burned hillslope after the Buffalo Creek Fire.  Photo by John A. Moody Photo of rill erosion on a burned hillslope after the Buffalo Creek Fire

 

For More Information

U.S. Geological Survey

USGS Water Resources

National Research Program

USGS Water Resources Division, Central Region

Geomorphology and Sediment Transport - River Mechanics

Mathematical Modeling Principles

Sediment-Water in Large River Systems: Biogeochemical, Geomorphic, and Human Controls

Midcontinent Ecological Science Center

Selected Publications and Abstracts

 

 


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