FLOOD05212

• County: Larimer
• Community: Fort Collins
• Stream Name: Boxelder Creek, Spring Creek, Dry Creek
• Basin: South Platte
• Title: Flood Control for Boxelder Creek at Fort Collins
• Date: 2/1/1993
• Prepared For: Fort Collins
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Table &.1
DISCHARGES COMPARISON WlTH AND WiTHOUT 100-YEAR DIVERSION
DISCHARGE IN CFS

LOCATION

MOUTH

UISAIRPAAK

U/SAlRPORT

DISVINE

VlNEROAO

LEMAY AVE

lAKE CANAl

DISCOLLEGE

UfSCOLLEGE

DISWElD
om"

UISWElD
om"

CONDITION

WIOUTOIV
WfDlV

WIOUTDIV
WIDIV

WIOUTOIV
W/DIV

WIOUTDIV
W/OIV

WIDUTDIV
WIDIV

WIOUTDIV
WIDIV

WIOUT DIV
WfDlV

WIQUT DIV
W/DIV

W/OUTDIV
WIDIV

WIDUTDIV
WIOIV

WIOUT DIV
WfDlV

2.YR

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so
so

>YR

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,so

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lD-YR So.YR

501 2237
414 634

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no

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,

1172
1172

""
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2215
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2236
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2236
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3113
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3125
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3138
,

3613
3513

100-YR

""
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3327
'"

3327
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3360
'"

3360
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3363
'"

3324
'"

''''
'"

4533
'"'

4547
,

SO"
5022

Noles: 1} Di$chargas8reforlullydevelopedcond~ions,
2) Oisc"arges between College Avenue and Lake Canal decrease due to
oveniow into Ine Poudre River over Ine Josh Ames D~ch

.

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6-7

-

SOo-YR

replacement of existing conduits under road crossings. Thes.e are measures the City
could implement. In addition, the City could construct a channel through the
undeveloped area between College Avenue and North LeMay Avenue as part of its
long~nnge flood control plans as development occurs in the area. Currently, this
reach has no Dry Creek ehannel. These measures were not included as part of the
reconnaissance-level plan because it appears that they would not be economically
feasible.
With the 30-yearplan in place, Dry Creek discharges would he significantly
reduced from Larimer and Weld Canal to its confluence with the Cache La Poudre
River. Tahle 6-2 shows a comparison of discharges foreltistingconditions and with
diversion of flows. The water surface profiles for Dry Creek also reflect a reduction
in stage from Larimer and Weld Canal downstream to the mouth for the with-
diversion channel condition.

.

7160
n"
7101
'''"'

7101
'''"'

7167
1058

7167
1058

7167
""

7112
1014

8S27
1520

The City of Fort Collins and/or Larimer County could improve the Dry Creek
channel in the Fort Collins Airpark area by regulating and/or climinating the
bottlenecks in the channel, replacing inadequately sired culverts under roads, and
clearing the channel of debris.

8931
1536

8947
1551

''''
9422

The effects the channel diversion would have on flooding on thc Cache La
Poudre River were also evaluated. Starting water surface elevations on the Cache
La Poudre River with a diversion channel along alignment B were determined from
rating Curves developed during the recent flood insurance restudy of the Cache La
Poudre River through Fort Collins. Data ohtained from "Hydrologic Analysis of the
Cache La J'oudre River Basin" dated April 1988, indicated that the lOO-year
discharge along the Cache La Poudre River between the confluence of the diversion
channel and Dry Creek would increase from about 13,300cfs 10 16,600cfs. Based

6-8

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