FLOOD10355

• County: Statewide
• Stream Name: Colorado River
• Title: Colorado River Basin Probable Maximum Floods, Hoover and Glen Canyon Dams
• Date: 9/1/1990
• Prepared By: US Department of the Interior Bureau of Reclaimation
• Floodplain - Doc Type: Floodplain Report/Masterplan

4.0 Antecedent Flood Analysis 47
4.1 General . . . . . . 47
4.2 Methodology for Developing the Antecedent Floods 47
4.3 Antecedent Floods for Hoover and Glen Canyon 48
4.4 Monthly Inflows to Major Upper Basin Reservoirs 56

5.0 Depletion Analysis 61
5.1 Background 61
5.2 1985-Level Depletions Above Glen Canyon 61
5.3 Depleted Monthly Antecedent Flood Flow for
Glen Canyon ........... 62
5.4 Daily Depletions for Glen Canyon Dam 63
5.5 1985-Level Depletions for Reservoirs Upstream
from Glen Canyon . . . . . . . . . . . . . . 66
5.6 Depleted Monthly Antecedent Flood Inflows for
Reservoirs Above Glen Canyon 67

1.0

2.0

3.0

6.0

TABLE OF CONTENTS

Summary

S-l

Introduction
1.1 Authority and Background
1.2 Study Scope and Participants
1.3 Basin Description
1.4 Historic Floods in the Colorado River Basin
1.5 Previous Studies

1
1
2
3
7
8

Meteorological Analysis
2.1 Introduction ....
2.2 Data Collection
2.3 Design Rainstorm Scenario
2.4 Magnitude of Uldrs
2.5 Spatial and Temporal Distributions of Uldrs
2.6 Storm Sequences
2.7 Seasonal Variation

17
17
17
18
19
21
21
26

Hydrologic analysis
3.1 Basin Field trips
3.2 Subbasin Delineation
3.3 Basin Parameters
3.4 Loss Rates
3.5 Lag Coefficients - "C"
3.6 Travel Times
3.7 Dimensionless Graphs

. . . . . . . . . . . .

29
29
30
30
36
39
39
40

Factors

Basin
6.1
6.2
6.3
6.4
6.5

Modeling ......
"Fhar" - Computer Program
Reservoir Operating Criteria
Reservoir Routing of 100-Year Snowmelt Flood
Glen Canyon and Hoover Probable Maximum Floods
Peak Discharge Envelope Curve

69
69
69
72
73
97

8.0 Acknowledgements

101

9.0 References

103

i