FLOOD10506

• County: Statewide
• Basin: Statewide
• Title: State of Colorado - 2006 Flood Documentation Reports
• Date: 6/1/2007
• Prepared For: CWCB
• Prepared By: ICON Engineering
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Flooded Area Description

As mentioned in the Introduction section of this report, flooding was reported in and
around the town of Penrose as well as several other areas within Fremont County. Most
of the damage occurred at bridge/culvert crossings along county roads and state
highways. Figure 1.2 shows the Penrose and Fremont County area in relation to the areas
where damage was reported.

Location and Watershed Description

Eightmile Creek, Brush Hollow Creek, and Beaver Creek are all north-bank tributaries of
the Arkansas River. The points of confluence for these creeks with the Arkansas River
all occur within an 8-mile reach of the river just downstream ofthe Town of Florence.

Eightmile Creek is a large north-south tributary to the Arkansas River which runs through
mostly unincorporated areas of Fremont and Teller counties. Its drainage area at the
Arkansas River is estimated at 63.4 square miles and has several road crossings near its
downstream end including various county roads as well as a large bridge crossing at
Highway 50. Approximately 70% of its drainage area lies within the mountainous
sparsely populated region to the north of the Arkansas River.

Roughly 1/3rd ofthe Brush Hollow Creek Basin is controlled by the Brush Hollow Creek
Reservoir which was constructed in the 1920's as an irrigation supply reservoir. While it
is on the main stem of Brush Hollow Creek, it is largely fed by a canal system that
transfers water from the Beaver Creek Basin to the reservoir. Approximately 8.2 square
miles of the Brush Hollow Creek basin drains to the reservoir. At the time of the July
2006 flood event, the water-surface elevation within the reservoir was fairly low allowing
for enough storage capacity such that no flows were released from the outlet works or
from the spillway during the flood event. An additional drainage area of approximately
12.3 square miles spans the area between the Highway 115 road crossing along Brush
Hollow Creek (Damage Area 7 on Figure 1.2) and just downstream of the reservoir. This
location is approximately Yz mile above the creek's confluence with the Arkansas River.

Although only minor damage was reported along Beaver Creek, it is included in this
report primarily due to the presence of a USGS Gage Station located along the
drainageway. Station 07099060 is situated on the left bank of Beaver Creek 300 feet
downstream from the Beaver Park Irrigation Company diversion dam, and 1.8 miles
upstream of State Highway 115 (See Figure 1.2). Tributary drainage area to this gage
station is approximately 138 square miles.

ICON Engineering, Inc

2

September 2006