RMRS - BAER Road Treatment Tools - Curve Number Methods Example

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Moscow Forestry Sciences Laboratory 1221 South Main Street Moscow, ID 83843 (208) 882-3557 7:30-4:30 M-F

BAER Tools -> Post-Fire Road Treatment Tools -> Post-Fire Peak Flow and Erosion Estimation -> Curve Number Methods -> Example

Example Results for Curve Number Methods: the 2005 Blackerby Fire in the Nez Perce National Forest, Idaho

The Blackerby Fire on the Nez Perce National Forest near Grangeville, Idaho occurred in August 2005. On 19 May 2006, a 0.79-inch precipitation event with a 30-minute duration occurred over a portion of the burned area. The precipitation event was equivalent to a 25-year, 30-minute storm event as determined from the NOAA Atlas 2 (Miller and others 1973).

	Precipitation (inches)

Return interval	Rainfall duration
	30 minute	6 hour	24 hour

2-year	0.32	0.9	1.6
5-year	0.47	1.1	2.0
10-year	0.63	1.3	2.4
25-year	0.79	1.5	2.9

The NRCS CN flood flow model results used in the BAER analysis (using FIRE HYDRO) were for a 25-year return event and based on the assumption of limited soil and vegetation regeneration during the first year after the fire (Gerhardt, 2006). The observed flood discharge value was 71 cfs or 56 cfsm (cfs mi^-2). This observed flood discharge was half that of predicted flow. Additionally, the observed debris flow discharge was 620 cfs, or 492 cfsm, indicating that debris flow discharge was nearly an order of magnitude greater than the flood discharge.

Storm	Estimated peak flow rate using FIRE HYDRO
return interval	cfs	cfsm

2-year 24-hour	23	18
5-year 24-hour	50	40
10-year 24-hour	85	67
25-year 24-hour	138	109

Storm	Observed peak flow rate
return interval	cfs	cfsm

25-year 30-minute	71	56

REFERENCES

Gerhardt, Nick. 2006. [Unpublished report]. December 18. Characterization of a post-fire debris flow and flood, Blackerby Fire, Idaho.

Miller, J. F.; Frederick, R. H.; Tracey, R. J. 1973. NOAA Atlas 2. Precipitation-frequency atlas of the western United States. Volume V-Idaho. Silver Spring, MD: NOAA.

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