FLOOD07708

• Designation Number: 317
• County: Boulder
• Community: Unincorporated Boulder County
• Stream Name: Bullhead Gulch and Tributaries
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Bullhead Gulch and Tributaries
• Date: 7/1/1991
• Designation Date: 11/1/1991
• Floodplain - Doc Type: Floodplain Report/Masterplan

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TABLE OF CONTENTS

Title

Pal!:e

LIST OF TABLES
Table Pal!:e
Table 1 - Study Reach Descriptions . , . . . , , , . . . , . . . . . . . . . , . . . . . . . . . . .. 3
Table 2 - Infiltration Loss Rate Data ."...",.....,........."...... 4
Table 3 - One-Hour Rainfall Depths for Zone I, Boulder County .,.,'......., 6
Table 4 - Percent Impervious for Various Land Uses. . . , . . . . . . , . , , . . . . . . ., 6
Table 5 - Summary of Basin Hydrologic Data Used in CUHPE Model ...,..... 8
Table 6 - Summary of Routing Element Data Used in SWMM Model. . . . . . . . .. 9
Table 7 - Summary of Hydrologic Analysis for Future Conditions. . . . . . . . , , ,. 10
Table 8 - Flood Plain and Floodway Reference Data "..........,..""...13

1.0 INTRODUCTION. . . , , , , . . . . . , . . . . . . . . . . . . . , , . . . . . . . . . . . . . , . . 1

1.1 AUTHORIZATION. ." . , .,. ., . . . .. . .., . . '" . ", ., .. .. . . ,. 1

1.2 PURPOSE AND SCOPE , , . , . . . . . . . . , , . . . . , . . , , , . . . . . . . . . . , 1
1.3 ACKNOWLEDGEMENTS , . . . . . . . . . . . , . . . , . , , . . , . . . . . . . . . " 2
1.4 PREVIOUS STUDIES, , . . . . . . . , , . . . . . , , , . . . . . . . . . . . . , , , . . . 2

2.0 STUDY AREA. , . . , . . , , , . . . . . , . . , . . , . . , . , . . . . . . . . . . . . . . . . . . . . 3

2,1 STUDY LIMITS. . , , . , . . . . . . , . . , . . . , , , . , . . . . . . . , . . , , , , . . . 3

2.2 STUDY AREA DESCRIPTION .,."",...,.......",........ 3
2.2 WATERSHED CONDITIONS ..........,.........,.".....,. 4

2,3 FLOOD HISTORY , , , . . . . . . . , , . , . . , , , , . . . . . , . . . , , . , , , , . . . 5

2.4 FLOOD MITIGATION MEASURES "..."...,.,...,...."", 5

LIST OF FIGURES

3.0 HYDROLOGIC ANALYSIS. . . . . , . . . , . , , , . , , , . . . . . . . . . . , . , . , , . .. 6

3,1 METHODOLOGy.,...,..,..., .". ..",'...,.' ..,. ,.,. .. 6

3.2 RAINFALL. , . . , . . . . . , , , , , . . . . . . . . . . . . , , , . . , . . . . . , . . . " 6

3,3 BASIN AND ROUTING DATA. , . , , , , . . . .. . . . .. . ., , , " . , . . .. 6

3.4 RESULTS. . . , , , . . , . . . . , . . . , . , . . . . . , . . . . , , . . . . . . . . . . . , 10

Figure 1 - Vicinity Map
Figure 2 - Municipal Boundaries
Figure 3 - Hydrologic Soil Types
Figure 4 - Wetland Delineation
Figure 5 - Future Impervious
Figure 6 - Outfall Sub-Basin Map
Figure 7 - SWMM Schematic (Sheet 1 of 2)
Figure 8 - SWMM Schematic (Sheet 2 of 2)
Figure 9 - Discharge - Probability Profiles

4.0 HYDRAULIC ANALYSIS ",..,...,.",,'.,.........'.,.,..... 11
4.1 PREVIOUS STUDIES, , , . . . . . . . . . . . , , , . . , , . . . . . . . . . . . , , . . 11

4,2 FLOODPLAINS, , , . . . . . , , , , . . . , . . . . , . . , , . . . , . . . . . . . . . .. . 11

4.3 FLOOD DAMAGES .,.........""......,.....'",..,.,. 12

APPENDIX

1()()-Year Floodplain Delineations

7.0 REFERENCES. . . , . . , . . . . , . . , . . , , . . . , , , . , . . . . . . . . . , . . , . . . . . 20

FLOOO HAZARD AREA DELINEATION
BUll.IIEAD GULCH AND lRIBUTARIES

FINAL
7!31191

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