FLOOD05064

• Designation Number: 205
• County: Larimer
• Community: Fort Collins
• Basin: South Platte
• Title: Master Drainageway Planning - Cooper Slough, Boxelder Creek, Fort Collins, Larimer County, Colorado
• Date: 8/1/1981
• Designation Date: 1/1/1983
• Floodplain - Doc Type: Floodplain Report/Masterplan

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imp~ovements a~e not justified by the benefit cost ratio. Howevep, it is
suggested that the channel cpossing undep the Lake Canal flume be enlapged to
capfy the 2,000 cfs fpom I-25 and Coopep Slough and ppevent watep fpom ovep-
topping the canal.
Fpom State 'Highway 14 to Willox Lane the floodplain is nappow. Limited
flood damage occUPS along this peach and imp~ovements ape not economically
justified. But it is suggested to enla~ge the capacity at the Lapimep-Weld
Ditch to ppevent the flood watep fpom oveptopping the canal and avoid othep
potential ppoblems.
Implementation of these plans should take place in a sequential mannep
that is coopdinated with development. The detention ponds along Coopep Slough
should be constr>ucted at Highway 14 and the Color>ado and Souther>n RaiZr>oad
fir>st. This will p~ovide pr>otection neap Highway 14 against the .sO-yeap
flood, and to some extent the 100-yeap flood, for> existing conditions.
Channel imppovements along Cooper> Slough fr>om the confluence of Boxelder> Cr>eek
to Highway 14 should be the second phase impr>ovements. These wauld p~event
Cooper> Slough fr>om flOUJing into Lake Canal duPing high flows. Channel imppo-
vements along Boxelder> below I-25 ar>e r>equir>ed to convey the flow fPOm I-25.
F:nla~ged openings at Lake Canal and LaPimer>-Weld Ditch cpossings ar>e r>equiped
to pr>event flood water> fr>om weir>ing oP possibly mixing with ditch watep.
These impr>ovements would be the thipd phase. Downstr>eam of Pr>ospect Str>eet.
impr>ovements should OMUP at an ear>Ziep time due to the impending development
of the p1'Oro""d sZudge application apea. The final impPOvements would be the
constr>uction of the detention ponds upstpeam of Vine Dpive as the apea
under>goes development.

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III.

TABLE OF CONTENTS

page

EXECUTIVE SUMMARY

ii

LIST OF TABLES

ix

LIST OF FIGURES

xii

LIST OF PLATES

xiii

I.

INTRODUCTION

Objectives
Purpose and Scope
Authorization . .
Acknowledgments .
Mapping and Surveying
Report Acquisition
Related studies . . .

1
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2
3
4
4

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II.

BASIN CHARACTERISTICS

Basin Description . . . . . . . .
Study Area . . . . . . . . . . .
Irrigation Ditches, Roads and Railroads
Soils . . . .
Water Quality
Flood History

5
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9
10
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10

HYDROLOGIC AND HYDRAULIC SUMMARY

Flood Characteristics
Hydrologic Analysis .

12
12

Rainfall Data .
Drainage Basin Parameters
Results . . .

14
14
21

Hydraulic Analysis
Floodway . . . . .

29
35

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IV. FLOODPLAIN INFORMATION

Flooded Areas

48

V. FLOOD DAMAGES

50

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