FLOOD01621

• County: Statewide
• Community: State of Colorado
• Title: Flood Hazard Delineation on Alluvial Fans and Urban Floodplains
• Date: 1/1/2001
• Prepared For: State of Colorado
• Prepared By: J.S. O'Brien
• Floodplain - Doc Type: Educational/Technical/Reference Information

I.

II.

TABLE OF C())lTl~NTS

.paae

List of Figures

ii

List of Tables

iv

INTRODUCTION

1

BACKGROUND .

2

III. PHYSICAL PROCESSES OF FLOOD 1!1l.Zl~DS
ON ALLUVIAL FANS . . .

3.1
3.2
3.3
3.4

4

Alluvial Fan Evolution
Description of Alluvial
Flow Paths and Avulsion
Return Period Frequency

Fan Flows

4
5
8
8

for Alluvial Fan Events

IV. FEMA METHODOLOGY FOR DELINEATING FLOOD HAZARD AREAS

ON FANS . . .. ...."... .... 10

4.1
4.2
4.3

V.

The Need for Flood Hazard DE,lineaticm
Description of FEMA's Me1:hodology
Assumptions and Limitations . . . " .

on Fans

10
10
12

TWO-DIMENSIONAL FLOOD SIMULA1'ION ON ALLUVIAL FANS

16

5.1
5.2
5.3
5.4

Advantages of Two-Dimensiclnal Modeling
Description of the FLO-;m Model
Model Theory . . . "
Model Limitations and Assumptions

16
16
19
22

VI. FLO-2D Model Verification

24

6.1 River Channel Hydraulics
6.2 River Overbank Flows, Floodplain Simulation -,
poudre River, Fort Collins, Colorado
6.3 Verification of Mudflow Hydraulics . " .

24

27
28

VII. Application of the FLO-2D ModE,1 _. Case Studies

32

7.1 Application Procedure . .. . . . . " . . " 32
7.2 Case Study - Hiko Springs Wash, Laughlin, Nevada.
Comparison with FEMA Methodology . " . . " ". 33
7.3 Case Study - Cornet Creek, Telluride, Colorado
Water Flooding and Mudflc,y/,s on a Urbanized Fan 37

VIn. CONCLUSIONS 44

IX. REFERENCES. . .

46

i