CLACKAMAS COUNTY, OREGON AND INCORPORATED AREAS Volume 1 of 3 Community Community Name Number BARLOW, CITY OF 410013 CANBY, CITY OF 410014 DAMASCUS, CITY OF 410006 *ESTACADA, CITY OF 410016 GLADSTONE, CITY OF 410017 HAPPY VALLEY, CITY OF 410026 *JOHNSON CITY, CITY OF 410267 LAKE OSWEGO, CITY OF 410018 MILWAUKIE, CITY OF 410019 *MOLALLA, CITY OF 410020 OREGON CITY, CITY OF 410021 RIVERGROVE, CITY OF 410022 SANDY, CITY OF 410023 WEST LINN, CITY OF 410024 WILSONVILLE, CITY OF 410025 CLACKAMAS COUNTY (UNINCORPORATED AREAS) 415588 *Non-floodprone EFFECTIVE: JUNE 17, 2008 Federal Emergency Management Agency FLOOD INSURANCE STUDY NUMBER 41005CV001A NOTICE TO FLOOD INSURANCE STUDY USERS Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood Insurance Study may not contain all data available within the repository. It is advisable to contact the community repository for any additional data. Old Zone New Zone A1 through A30 AE V1 through V30 VE B X C X Part or all of this Flood Insurance Study may be revised and republished at any time. In addition, part of this Flood Insurance Study may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the Flood Insurance Study. It is, therefore, the responsibility of the user to consult with community officials and to check the community repository to obtain the most current Flood Insurance Study components. TABLE OF CONTENTS – Volume 1 Page 1.0 INTRODUCTION.......................................................................................................................... 1 1.1 Purpose of Study................................................................................................................. 1 1.2 Authority and Acknowledgments ....................................................................................... 1 1.3 Coordination ....................................................................................................................... 2 2.0 AREA STUDIED ........................................................................................................................... 4 2.1 Scope of Study.................................................................................................................... 4 2.2 Community Description...................................................................................................... 5 2.3 Principal Flood Problems.................................................................................................. 16 2.4 Flood Protection Measures ............................................................................................... 19 3.0 ENGINEERING METHODS ..................................................................................................... 20 3.1 Hydrologic Analyses......................................................................................................... 21 3.2 Hydraulic Analyses........................................................................................................... 28 3.3 Vertical Datum.................................................................................................................. 29 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS.............................................................. 30 4.1 Floodplain Boundaries...................................................................................................... 30 4.2 Floodways......................................................................................................................... 32 5.0 INSURANCE APPLICATION................................................................................................... 88 6.0 FLOOD INSURANCE RATE MAP........................................................................................... 88 7.0 OTHER STUDIES....................................................................................................................... 89 8.0 LOCATION OF DATA............................................................................................................... 91 9.0 BIBLIOGRAPHY AND REFERENCES................................................................................... 91 i TABLE OF CONTENTS – Volume 1 (Cont’d) Page FIGURES Figure 1 – Floodway Schematic ................................................................................................................. 33 TABLES Table 1 – Detailed Study Streams............................................................................................................... 14 Table 2 – Summary of Stillwater Elevations .............................................................................................. 21 Table 3 – Summary of Discharges.............................................................................................................. 23 Table 4 – Clackamas County Vertical Datum Conversion ......................................................................... 31 Table 5 – Floodway Data............................................................................................................................ 34 Table 6 – Community Map History ............................................................................................................ 90 TABLE OF CONTENTS – Volume 2 EXHIBITS Exhibit 1 - Flood Profiles Abernethy Creek Panels 01P – 04P Clackamas River Panels 05P – 15P Clackamas River (without consideration of levee) Panels 16P – 17P Clear Creek Panels 18P – 19P Deer Creek Panels 20P – 21P Eagle Creek Panels 22P – 24P Johnson Creek Panels 25P – 30P Kellogg Creek Panels 31P – 33P Milk Creek Panels 34P – 40P Molalla River Panels 41P – 52P Mt Scott Creek Panels 53P – 55P Oswego Canal Panel 56P Phillips Creek Panels 57P – 59P Pudding River Panels 60P – 63P Richardson Creek Panels 64P – 69P Richardson Creek – Anderson Road Tributary Panels 70P – 74P Richardson Creek – Keller Road Tributary Panels 75P – 77P Richardson Creek – Royer Road Tributary Panel 78P Rock Creek Panels 79P – 89P Rock Creek – Hemrick Road Tributary Panels 90P – 93P Rock Creek – Highway 224 Tributary Panels 94P – 95P ii TABLE OF CONTENTS – Volume 3 Exhibit 1 - Flood Profiles (continued) Rock Creek – N Golf Course Tributary Panels 96P – 98P Rock Creek – S Golf Course Tributary Panel 99P Rock Creek – 172nd Avenue Tributary Panels 100P – 101P Salmon River Panels 102P – 108P Salmon River North Channel Panel 109P Sandy River Panels 110P – 126P Seely Ditch Panels 127P – 129P Springbrook Creek Panels 130P – 132P Still Creek Panels 133P – 137P Tickle Creek Panels 138P – 143P Tualatin River Panels 144P – 147P Tualatin River Overflow to Rivergrove Panel 148P Willamette River Panels 149P – 154P Zigzag River Panels 155P – 161P PUBLISHED SEPARATELY: Flood Insurance Rate Map Index Flood Insurance Rate Map iii FLOOD INSURANCE STUDY CLACKAMAS COUNTY AND INCORPORATED AREAS 1.0 INTRODUCTION 1.1 Purpose of Study This Flood Insurance Study (FIS) revises and updates information on the existence and severity of flood hazards in the geographic area of Clackamas County, including the Cities of Barlow, Canby, Damascus, Estacada, Gladstone, Happy Valley, Johnson City, Lake Oswego, Milwaukie, Molalla, Oregon City, Rivergrove, Sandy, West Linn, Wilsonville and the unincorporated areas of Clackamas County (referred to collectively herein as Clackamas County), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This study has developed flood-risk data for various areas of the community that will be used to establish actuarial flood insurance rates and to assist the community in its efforts to promote sound floodplain management. Minimum floodplain management requirements for participation in the National Flood Insurance Program (NFIP) are set forth in the Code of Federal Regulations at 44 CFR, 60.3. Please note that the Cities of Rivergrove, Tualatin, and Wilsonville are geographically located in Clackamas and Washington Counties, the City of Milwaukie is geographically located in Clackamas and Multnomah Counties, and the Cities of Lake Oswego and Portland are geographically located in Clackamas, Multnomah, and Washington Counties. The Cities of Lake Oswego, Milwaukie, Rivergrove and Wilsonville are included in their entirety in this FIS report. The Cities of Portland and Tualatin are published separately. Please note that the Cities of Estacada, Johnson City, and Molalla are non-floodprone. In some States or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum Federal requirements. In such cases, the more restrictive criteria or regulations take precedence, and the State (or other jurisdictional agency) will be able to explain them. 1.2 Authority and Acknowledgments The sources of authority for this FIS report are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. The hydrologic and hydraulic analyses for the original FIS for the City of Barlow, City of Canby, the unincorporated areas of Clackamas County, City of Lake Oswego, City of Oregon City, City of Rivergrove, and the City of Wilsonville, were performed by James M. Montgomery, Consulting Engineers, Inc., for the Federal Emergency Management Agency (FEMA), under Contract Nos. H-4583 and H-4582. These studies were completed in December, 1979, January, 1983, November, 1984, March, 1984, June,