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 Measured Debris Flow
Depths, Aug - Oct 2002 events,
Coal Seam Fire

160
140
III - Channel Depths
.... .=:120 -
.0
Q) =100
c Flood Plain Depths
c. "
"C ~ 80
Q) I
....
:l ~ 60
III - - Measured=Modeled
III 0
Q) ii: 40 S-- Data
~
20 -,-"
0 ',","'"".,
0 50 100 150

Flo.2D Depth in, 100 yr Storm

Figure 3. Modeled debris now depths plotted with measured debris now depths
for debris now events that occurred between August and October 2002.

Coal Scam Fire: Sing.lc Event Debris Flow 9-10-03

Debris now depths (0=20) were measured in 8 basins for a debris now event that
occurred on 9-10.03 within the Coal Scam fire arc.1 (Figure 4). Fresh mud lines were
measured on 9-16-03. This event had a maximum storm intensity of 0.17 inches per hour
with a tolal storm precipitation amount of 0.59 inches, which constitutes a 5 year stoml
event (RA WS, 2003). All measured data were within the range of depths predicted by
FLO.2D except for 2 points on the noodplain. These two points occurred on basin Red
Mountain 6 in the USGS report (Basin "0" in Cannon eL aI., 2003). The debris !low ill
this basin ran approximately 700 feet further than the FLO.2D model predicted. These
measurements arc shown on Figure 4 as the two points at 0, 18 and 0, 20 on the debris
now depth graph. FLO-2D has under.predicted the correct run out distance lor this
particular basin (Red Mtn 6). Note that this debris llow occurred with a 5 year recurrence
stoml event and the FLO-2D simulation was for a 100 year event. This shows that there
could be a large discrepancy for maximum run out distances on the Wulfsohn fan area.
Some of the basins on the Wulfsohn fan area, which include Red Mtn basins 1-7,9 and
II, Illay be under-predicted by FLO-20 for nm out distance of debris llows based on the