FLOOD00385

• County: Boulder
• Community: Boulder
• Stream Name: Boulder Creek
• Title: South Boulder Creek Interim Hydrology Study
• Date: 7/1/2000
• Prepared For: Boulder County
• Prepared By: Taggart Engineering Associates, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

II - 12

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
II
I

inches of precipitation from 31 August to 4 September with 2.32 inches
falling during 2 September. Eldorado Springs had 4.42 inches of
rainfall. Approximately 80 percent of the total precipitation falling in the
South Boulder Creek basin fell in the late afternoon and evening of 2
September. The resulting flood, with a peak discharge of 7,390 c.f.s.
arrived at Eldorado Springs at 10:00 p.m. on 2 September. The peak
gradually subsided as the flood moved downstream. A maximum
discharge of 4,410 c.f.s. occurred near the mouth of Boulder Creek at
noon on 3 September. Several buildings in Eldorado Springs were
destroyed as a result of the flood eroding away their foundations.
Numerous bridges were destroyed and the valley from Eldorado Springs
to Boulder Creek and down Boulder Creek to the St. Vrain Creek were in
shambles. This flood is the highest recorded flood on South Boulder
Creek. "

Phyllis Smith reports in "History of Floods and Flood Control in Boulder, Colorado"
on this event, with extensive photographs (by the Boulder Historical Society) of the
damage in Eldorado Springs. They depict destruction of buildings and movement of
rock in the 6 inch to 2 feet range. Ms. Smith notes that South Boulder Creek
flooded again the following year, but apparently there is no reported gage data.

We believe that there is sufficient watershed below Gross Reservoir to allow such
events, including large scale sediment and debris movement.

4-8 Mav 1969

The Corps also reported on this event in their 1969 study.

"This was also a flood of long duration general storm. Precipitation
was heaviest in the mountains; part of it being snow. In the Boulder
and South Boulder Creek basins the rainfall continued at a moderate rate
for nearly four days. Total precipitation for the storm amounted to 7.60
inches at Boulder and 9.34 inches at the Boulder Hydroelectric Plant
located about 3 miles up the canyon from Boulder. Precipitation
amounts totaled 8.11 inches at Eldorado Springs and 10.05 inches at
Gross Reservoir on South Boulder Creek. Peak flooding occurred on the
7th of May at Boulder and Eldorado Springs. Preliminary estimates
based on the gaging records, indicate a peak discharge of 1,150 c.f.s.
occurred on Boulder Creek. Flooding extended over large portions of the
flood plain starting at the junction of the two streams near Valmont
Road and extending downstream through the remainder of the Boulder
Creek study reach. Evidence of two bridge failures is illustrated.