FLOOD10504

• County: Garfield
• County: La Plata
• Community: Glenwood Springs, Durango
• Basin: Colorado Mainstem
• Title: Glenwood Springs / Durango Wildfire Documents
• Floodplain - Doc Type: Correspondence

Modeled vs Meaured Debris Flow Depths
8-17-03 Event, Missionary Ridge Fire

~ 200
iL .. 150
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0 100
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0 50 100

. Channel Depths

.

. Flood Plain Depths

.

-I

~ Measured=Modeled
Data

150

200

Flo.2D Depth, inches, 100 yr Storm

Figure 2. Modeled debris flow depths plaued with measured debris flow depths for debris
flow events that occurred on August 17. 2003.

Coal Scam Fire: Debris Flow Events- Fall 2002

Debris flow depth data (n=42) were collected in 9 basins in the Coal Sc.lm fire
area. The depths in Figure 3 were mc.lsurcu from the events of August. September and
October 2002 which had the largest amounts of rainfall and largest recorded debris flow
events within the lire perimeter (Cannon ct. aI., 2003). The FLO-2D simulations lIsed
inflow hydrographs based on the 100 year predicted rainfall event, which in the
Missionary Ridge area was 1.64 inches of rain in one hour. The debris now events from
2002 that were compared to the modeled results were 5 ye:'lr storm events or less, with a
maximum average stonn intensity of 0.67 inches per hour. The tolal stonn precipitation
amount ranged from 0.16 - 0.67 inches (RA WS 2003).
Nine measured debris now depths in 4 of the basins exceeded the calculated
depths for a 100 year debris now event (Figure 3). All but one of the measurement points
that exceeded the model predictions were in channels. Again this may be an under-
estimation ofdehris now depths by FLO.2D or it may be an artifact of greater debris
now depths in incised channels. The data arc somewhat disconcerting given the fact that
the measured stonn events have a five year recurrence interval (or less) and the FL042D
simulations were run for a 100 year event.