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ARS Home » Pacific West Area » Tucson, Arizona » SWRC » Research » Publications at this Location » Publication #163609
Title: MODELING SCOUR AND DEPOSITION IN EPHEMERAL CHANNELS AFTER WILDFIRE 1610

Author
item Canfield, Howard
item LANE, L. - RETIRED ARS
item WILSON, C. - LANL
item CROWELL, K. - LANL
item THOMAS, W. - MOBILE BOUNDARY HYDRAULIC

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2004
Publication Date: 6/30/2005
Citation: Canfield, H.E., Lane, L.J., Wilson, C.J., Crowell, K.J., Thomas, W.A. 2005. Modeling scour and deposition in ephemeral channels after wildfire. Catena. 61(2-3): 273-291.

Interpretive Summary: The area burned by wildfire in the states of Arizona and New Mexico in the southwestern US has been increasing in recent years. Increased runoff and sediment from burned watersheds has the potential to increase flooding, and sedimentation in reservoirs, which may be important for drinking water supplies in the desert southwest. Therefore, there is a need for a computer prediction tool to allow land managers to understand the potential impacts of wildfire on runoff, erosion and sedimentation. This paper describes the potential and limitations of the HEC6T sediment transport model applied to Pueblo Canyon, near Los Alamos, New Mexico following the Cerro Grande Fire. Following the fire this canyon was subject to a peak flow 100 times greater than any flow in the seven-year period for which data are available. HEC6T simulated the overall changes in scour and deposition in Pueblo Canyon. Therefore, this paper demonstrates that the HEC6T model can be used to predict post-fire impacts of fire on flooding, erosion and sedimentation. Furthermore, in describing how the model was applied, this paper shows scientists and land managers how to use the HEC6T model to predict post-fire flooding, erosion and sedimentation.

Technical Abstract: High severity burns have caused increases in runoff and sediment yield from burned watersheds in Arizona and New Mexico. This paper describes the potential and limitations of the HEC6T sediment transport model to predict changes in channel scour and deposition following wildfire. Following the Cerro Grande Fire, Pueblo Canyon, near Los Alamos, was subject to a peak flow twice the initial post-fire estimate of the 100 yr event. The limits of scour and deposition on a cross-section were specified in HEC6T by using predicted post-burn hydrology and long-term estimates of channel change derived from air photos. Erosion shear stress and rate parameters for cohesive sediments were obtained experimentally. An optimization routine was used to estimate the model parameter values for sensitive parameters. HEC6T was able to accurately model the overall change in cumulative sediment volume derived from Airborne Laser Swath Mapping (ALSM, often called Lidar) taken before and after the large post-fire event. One discrepancy between the HEC6T model prediction and the ALSM-estimated change was that the greatest amount of deposition was observed in a portion of the canyon with increasing slope. Any sediment transport model will predict increased sediment transport capacity with increasing energy slope, so that it was considered to be beyond the capability of any sediment transport model to predict this deposition. Therefore, HEC6T simulated the changes in scour and deposition within reasonable expectation of the capabilities of sediment transport models.