FLOOD00961

• County: Larimer
• Community: Fort Collins
• Stream Name: Spring Creek
• Title: Hydraulic Evaluation of the Centre Avenue Bridge at Spring Creek
• Date: 11/22/2000
• Prepared For: Fort Collins
• Prepared By: Anderson Consulting Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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the corrected effective and post-project condition models are indicated. The 100-year water
surface elevations are generally lower in the post-project condition analysis (from 0,1 to 0.4 feet)
upstream of the BNRR to Centre Avenue. as compared to the corrected effective analysis.
Directly upstream of Centre A venue, the post-project condition analysis matches the corrected
effective profile, Graphical representation of the post-project condition flood profiles through the
current study reach is provided in Appendix B, In addition, cross sections through the study reach
which were modified for the post-project condition analysis are graphically displayed in Appendix
C.

Table 4.4

Comparison of 100-Year Water Surface Profiles for Corrected Effective and Post-
Project Condition Analyses,

100- Year
HEC-2 Water Surface Elevation Difference
FIRM Cross (ft, NGVD) in WSEL Location
Panel ID
Section Corrected Post-Project (feet)
Effective Condition
16430 4993,5 4993.4 -0,1 upstream side of BNRR
embankment
BF 17380 4993,5 4993.4 -0,1
18075 4993.5 4993.4 -0,1
BG 18135 4993,5 4993.4 -0,1 downstream face of unnamed road
(Bay Road)
18168 4993,5 4993.4 -0,1 upstream face of unnamed road
(Bay Road)
18240 4993.5 4993.4 -0,1
BH 18625 4993,5 4993.4' -0,1
18770 4993,7b 4993,3 -0.4
BI 19337 4994,7 4994,7 0,0
19830 4997.4 4997.4 0,0 downstream side of Arthur Ditch
BJ 19880 4997,7 4997,7 0,0 upstream side of Arthur Ditch
BK 20315 4999,3 4999,3 0,0

, Based on interpolated post -project condition WSEL.
b Based on interpolated corrected effective WSEL.

For the post-project condition floodway analysis, floodway encroachments were modified
from those defined in the corrected effective model to reflect narrowing of the floodplain due to
the lower WSEL's associated with the post-project analysis, Results of the post-project condition
floodway analysis are summarized in Table 4,5, The table indicates that the floodway water
surface elevations are identical to the base flood elevations, thereby meeting the intent of the

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ANdERSON CONsulTiNG ENGiNEERS, INC,