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<br />..
<br />
<br />Many ofthe measured depths of post-fire d(:bris flows fall close to the line
<br />predicted by FLO-2D for a 100 year debris flow event. This is disconcerting given that
<br />the measured depths were from 10 year or less recurrence intervals. While many ofthese
<br />anomalies may be explained by channel incision, numerous points were measured on the
<br />flood plain where no incision occurred. It may be necessary to run the model for a lower
<br />recurrence interval, perhaps 5 to 1 0 years, in order to determine if the debris flow depths
<br />and run out distances pose a hazard to surrounding facilities at risk.
<br />There are a few areas where the FLO-2D debris flow run out distance predictions
<br />fall short of actual debris flow events that have already occurred. There may be other
<br />FLO-2D debris flow run out distances that under-predict future debris flow events in the
<br />Wulfsohn fan are ofthe Coal Seam Fire. I recommend that the simulations for the
<br />Wulfsohn Fan area ofthe Coal Seam fire be run again using different volumetric
<br />sediment concentration inputs in order to lengthen the run out distances for debris flows
<br />to more closely approximate run outs that have actually occurred.
<br />
<br />References
<br />
<br />Cannon, S.H., Gartner, J., Holland-Sears, A., Thurston, B., Gleason, J., 2003, DEBRIS-
<br />FLOW RESPONSE OF BASINS BURNED BY THE 2002 COAL SEAM AND
<br />MISSIONARY RIDGE FIRES, COLORADO, Engineering Geology in Colorado-
<br />Contributions, trends and case histories: Assoc. of Engineering Geologists Special
<br />Publication 14, on CD-ROM.
<br />
<br />Friedel, M., 2003, Personal communication regarding statistical analysis ofFLO-2D
<br />simulations.
<br />
<br />Miller, J. F., Fredrick, R.H., and Tracey, R.I, 1973, Precipitation-frequency atlas ofthe
<br />western United States, Vol. 3 - Colorado: US Dept.. of Commerce, NOAA, NWS, Silver
<br />Spring, MD.
<br />
<br />O'Brien, J., 2002, Flo-2D Users manual, Version 21001.6, PO Box 66, Nutrioso, AZ.
<br />
<br />RAWS, 2003, Remote Automatic Weather Station, National Weather Servic(: fire weather
<br />data archive, http://raws.boi.noaa.gov/obs2/ .
<br />
<br />Smith, M.E., J.G. Elliott, M.J. Friedel, D.W. Litke, M.R. Stevens, C. Costello, S.J. Char,
<br />(U.S. Geological Survey), and J. Wagner (Bureau of Reclamation), 2003, POST-FIRE
<br />HYDROLOGIC HAZARDS STUDY FOR THE 2002 HAYMAN, COAL SEAM, AND
<br />MISSIONARY RIDGE WILDFIRES, COLORADO, USGS Administrative: Report, July
<br />2003.
<br />
<br />Thurston, B., 2002, Flow characteristics, precipitation data and discharge estimates for
<br />the Missionary Ridge fire area, August and September 2002, USGS internal report,
<br />(unpublished).
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