Upper Yakima River Comprehensive Flood Hazard
Management Plan


June 2007 Update

TABLE OF CONTENTS

 

Front Cover

 

Inside Cover

 

Title                                               

Page No

Acknowledgments

i

Table of Contents (this document)

ii

List of Tables

vii

List of Figures

ix

List of Abbreviations

xi

Executive Summary

ES-1

CFHMP Background

ES-1

CFHMP Goals and Objectives

ES-2

CFHMP Update

ES-4

Recommended Actions

ES-6

Implementation Strategy

ES-6

Large Project Implementation Strategy

ES-13

1.  Introduction

1-1

Background

1-1

Flooding Issues in Study Area

1-1

Principles of Flood Hazard Management

1-2

Authority and Scope for Yakima County CFHMP

1-2

Plan Development Process

1-4

Involving the Public and Affected Agencies

1-4

Defining Goals and Objectives

1-8

Collecting Data

1-8

Related Programs or Actions

1-11

Plan 2015 - Yakima Countys Comprehensive Plan

1-11

Yakima County Revised Flood Insurance Study

1-11

Flood Control Assistance Account Program

1-11

Funding

1-12

Requirements for CFHMPs

1-12

Applicant Eligibility

1-13

Maintenance Project Eligibility

1-13

Emergency Projects

1-14

Required Consultation with Other Agencies

1-14

2.   Study Area Characteristics

2-1

Yakima River Basin

2-1

Study Area Limits

2-2

Upper Reach - Yakima Canyon to Selah Gap

2-2

Middle Reach - Selah Gap to SR 24 Bridge

2-4

Lower Reach - SR 24 Bridge to Union Gap

2-5

Physical Characteristics

2-5

Climate

2-5

Hydrology

2-5

Geology

2-8

Soils

2-10

Wetlands

2-11

Fisheries and Wildlife

2-11

Vegetation

2-12

Water Quality

2-13

Socioeconomic Characteristics

2-15

Jurisdictional Boundaries

2-15

Population

2-15

Land Use

2-16

3.   Previous Studies

3-2

Revised Preliminary Yakima County Flood Insurance Study

3-2

Estimated Flood Flows

3-2

Hydraulic Computer Modeling

3-7

Flood Insurance Rate Maps, Floodway Maps, and Flood Boundary Maps

3-8

1970 Floodplain Information; Yakima and Naches Rivers

3-9

1973 Floodplain Information; City of Selah and Vicinity

3-9

1978 Yakima-Union Gap Flood Damage Reduction Report

3-10

Alternative 1 - No Action

3-10

Alternative 2 - Floodplain Management Alone

3-10

Alternative 3 - Floodplain Management with Additional Flood
Control Storage

 

3-10

Alternative 4 - Floodplain Management with Levees

3-12

Alternative 5 - Floodplain Management with Channel Modification

3-12

Alternative 6 - Purchase of Development Rights

3-12

Alternative 7 - Purchase of Floodway

3-12

Recommended Plan

3-13

1986 Yakima-Union Gap Flood Control Project

3-14

1991 Yakima River Flood Evaluation for Yakima County Diking District No. 1

3-14

Estimated Flood Flows

3-15

Review of Historical Floods

3-15

Issues Identified as Affecting Flood Risks

3-16

Assessment of Previous Studies

3-16

Key Results from Previous Studies

3-17

Recent Related Studies

3-18

1998 Department of Natural Resources Flood Plains, Salmon Habitat,
and Sand and Gravel Mining

 

3-19

1998 Department of Natural Resources Reclamation of
Flood-Plain Sand and Gravel Pits and Off-Channel Salmon Habitat

 

3-19

1998 Revisions to Yakima County Flood Insurance Study

3-19

Yakima River Floodplain Mining Impact Study (2002)

3-19

The Reaches Project Report (2002)

3-21

SR 24 Project Floodplain Consistency Report (2003)

3-23

Lower Naches River Coordination Project (2005)

3-23

Yakima County Mineral Resource Task Force (2006)

3-26

Conclusions - Additional Ongoing Efforts that Affect Flood Management

3-27

2003 Yakima River Basin Water Storage Feasibility Study

3-28

Subbasin Plan and Salmon Recovery

3-28

4.  Yakima River Flooding Characteristics

4-1

Common Flood Characteristics

4-1

Flood Magnitude

4-1

Flood Duration

4-2

Channel Migration

4-3

Sediment Transport and Deposition

4-4

Effects of Levees

4-8

Effects of Roads and Bridges

4-8

Effects of Reservoir Storage

4-9

Flood History

4-9

February 9, 1996, Flood

4-10

November 30, 1995, Flood

4-14

February 1995 Floods

4-14

November 26, 1990, Flood

4-15

December 27, 1980, Flood

4-18

December 2, 1977, Flood

4-18

December 4, 1975, Flood

4-19

January 16, 1974, Flood

4-19

March 14, 1972, Flood

4-20

May 29, 1948, Flood

4-20

December 23, 1933, Flood

4-21

Summary of Historical Floods

4-21

Historical Flood Improvement Projects

4-22

5.   Flood Control Facilities and Programs

5-1

Facilities Inventory

5-1

Yakima Levee Project

5-1

Public Law 84-99 Levees

5-2

Highways

5-4

Other Flood Control Works

5-6

Operation and Maintenance

5-11

Special Districts

5-11

Other Flood-Related Programs

5-11

United States Bureau of Reclamation, Yakima Project

5-12

Yakima Greenway Foundation

5-13

Yakima River Watershed Council

5-20

Yakima River Basin Water Enhancement Project

5-20

Yakima Subbasin Fish and Wildlife Planning Board (YSPB)

5-21

Yakima Basin Salmon Recovery Board Lead Entity

5-21

Yakima Basin Fish & Wildlife Recovery Board

5-21

6.  Regulations

6-1

Summary of Existing Regulations

6-1

County Regulatory Tools for Flood Hazard Management

6-8

City of Yakima

6-11

City of Union Gap

6-11

City of Selah

6-12

NPDES Phase II Municipal Stormwater Permits

6-13

Permitting Requirements

6-14

SEPA/GMA Integration

6-14

7.  Alternative Analysis Approach

7-1

Flooding Issue Identification

7-1

Flood Hazard Management Options

7-1

Nonstructural Measures

7-1

Structural Measures

7-3

Alternative Analysis and Selection

7-4

Considerations for Evaluating Alternatives

7-4

Alternative Selection

7-7

8.  Analysis of Flood Mitigation Alternatives

8-1

LR5 - Aggradation/Reduced Flood Capacity Upstream of SR 24 Bridge;
Flood Damage to SR 24 Bridge, Yakima Regional Wastewater Treatment
Plant Levee, and DID #1 Levee (1)

 

 

8-3

MR2 - Yakima Beech Street Gravel Pit Levee (2), and
UR5 - East Selah Gravel Pit Levee (24)

 

8-25

LR3 -  Increased Flood Elevation near Union Gap (3)

8-30

LR7 - Capture of Edler Ponds (4)

8-37

RW1 - Floodplain Mapping (5)

8-38

RW20 - Loss of Channel Capacity due to Sediment Accumulation (6)

8-42

NA1 - Bedload Movement and Channel Instability of Naches River (7)

8-43

RW13 - Funding for Flood Control Work and Restoration Projects (8)

8-44

RW6 - Public Disclosure of Floodplain Status (9)

8-45

RW12 - Protection of State and County Roads (10)

8-46

RW3 - Channel Migration (11), LR1 - Erosion of Agricultural Lands (15), and
UR1 - Erosion of Agricultural Land (22)

 

8-49

RW9 - Diversity of Opinions Relating to River Management (12), and
RW8 - County Policy on Flood Hazard Management (17)

 

8-50

RW4 - Flood Hazard Ordinance (13), and
RW5 - Revision and Consistency of Critical Areas Ordinance (25)

 

8-51

RW2 - Loss of Fisheries Habitat and Riparian Areas (14), and
MR8 - Borrow Pit Levee Upstream of Terrace Heights Bridge (31)

 

8-61

RW17 - Existing Structures in the Floodplain (16)

8-64

RW16 - Operation and Maintenance of Flood Control Facilities (18)

8-67

RW10 - Acquisition/Preservation of Floodplain Open Space (19)

8-70

RW19 - Flood Warning and Emergency Response (20)

8-73

RW18 - Community Rating System (21), and
RW7 - Flood Insurance and Public Education (28)

 

8-79

RW15 - Use of Geographic Information (GIS) Data (23)

8-84

OSA1 - Continued Flood Damage Outside the CFHMP Study Area (26)

8-88

MR6 - Flood Damage to Greenway path Near Boise Cascade Pond (32)

8-89

LR6 - Spring Creek Backwater Flooding (29)

8-92

MR7 - Flood Damage to Robertson Landing (30), UR3 - Flood Damage
to Harlan Landing (33), and UR4 - Inundation of Elks Golf Course (34)

 

8-94

9.  Funding Options

9-1

Funding Sources

9-2

County Administrative Options

9-2

External Funding Sources

9-10

Funding Source Evaluation

9-23

Evaluation Criteria

9-23

Programs to be Funded

9-24

Large Project Funding Strategy

9-27

References

R-1

Appendices 

A.   Yakima County Flood Control District’s Response to  Mitigated Determination of Non-Significance (MDNS),   and July 22, 2005 SEPA Final Mitigated Determination of Non-Significance issued from Yakima County Planning Services Division

B.  Issues contained in the 1998 Upper Yakima CFHMP but removed from the 2007 Update and New Issues Contained in the 2007 update that were not in the 1998 CFHMP

C. February 9, 1996, Flood Inundation Maps

Map C-1  North Section

Map C-2  Central Section

Map C-3  South Section

D.  Flood Control Works Inventory

Map D-1   Overview of levees within the planning area

Table - Status of Inventoried Levees

Map D-2   Federal Project Levees – Right Bank Upper

Map D-3   Federal Project Levees – Right Bank Lower

Map D-4   Federal Project Levees – Left Bank

E.  Advisory Committee Voting Results