FLOOD00859

• County: Boulder
• Community: Boulder
• Stream Name: Bullhead Gulch
• Title: Bullhead Gulch Hydrology Report
• Date: 3/4/1995
• Prepared For: FEMA
• Prepared By: Taggart Engineering Associates, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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BULLHEAD GULCH HYDROLOGY REPORT
ADDENDUM NO. 1

Per comments from Centennial, Engineers for the Town of Erie, the following two
changes are made to the Bullhead Gulch Hydrology Report, August 22, 1997:

1. The SWMM model was changed (new model is named "bh100fi4.sin/.sot," the
printout for the 1 OO-year is included): Routing element 49, which receives runoff
from basins 47 and 48 (south of Arapahoe Ridge) and from basin 49 (west of
Arapahoe Ridge) has been changed to circumvent the Arapahoe Ridge pond and
connect with Prince tributary just downstream of the pond. During our November
13, 1997 telephone_conversation, Mr. Tom Fuentes (Centennial) said that those
flows from basins 47, 48, 49 do not enter the Arapahoe Ridge development or
pond, but run along 111th street. No analysis has been done to determine where
those flows finally enter Prince Tributary. Please note that the CUHP runoff
analysis did not change, therefore the "bh 1 OOfi4.sin" model should be run with
the CUHP file "bh100fi3.chd."

TEA was directed to use the Urban Drainage and Flood Control District Flood
Hazard Area Delineation Study (FHAD) SWMM model as a basis for the FIS, with
corrections for storages and other watershed/ channel changes. The FHAD
shows element 49 entering Prince Tributary at the Middle of Section 26, which is
just downstream of the new Arapahoe Ridge Development. The exact flow
pattern for element 49 is not clear from UDFCD mapping or from design contours
for 111 th Street / Aprapahoe Ridge. For the purposes of this FIS, the flows are
assumed to enter Prince Tributary just downstream of the Arapahoe Ridge
detention pond.

1

Modified Figures 2 (2/2).3,5 and Modified Table 2 (included) reflect this change.
Impact of this change was minimal, as can be seen by comparing these modified
versions with the original versions in the report. We will use the modified flows
to maintain consistency with the Town of Erie.

2. Add the following sentence to item 1., page 1.:

Percent impervious in the FIS was also compared to land use in the Erie
Comprehensive Plan, 1996, and was found to be generally in agreement. (See
Appendix H in original report,)