Little Colorado River, Winslow, Arizona May 2016
Total Page:16
File Type:pdf, Size:1020Kb
US Army Corps of Engineers® Los Angeles District LITTLE COLORADO RIVER WINSLOW, ARIZONA FLOOD RISK MANAGEMENT PROJECT DRAFT INTEGRATED FEASIBILITY REPORT WITH ENVIRONMENTAL IMPACT STATEMENT May 2016 This page left blank for duplex printing Little Colorado River Winslow, Arizona Flood Risk Management Project Draft Integrated Feasibility Report (Feasibility Report/Environmental Impact Statement) Navajo County, Arizona Lead Agency: U.S. Army Corps of Engineers, Los Angeles District (Corps). Abstract: This Draft Integrated Feasibility Report (Draft IFR) evaluates alternatives to reduce the risk of damages and to reduce the life, safety, and health risks caused by flooding of the Little Colorado River (LCR) to the City of Winslow, surrounding community, and public and private infrastructure. The Draft IFR documents the plan formulation and environmental impact analysis conducted by the Corps in close cooperation with Navajo County Flood Control District, the non-Federal sponsor for this study. The LCR at Winslow study area is located in the middle of the LCR Watershed, in and near the City of Winslow in western Navajo County, Arizona. The study area includes the floodplain of the LCR from the Clear Creek confluence downstream (northwest) to the northern end of the existing Winslow Levee. The 49-square-mile study area encompasses the City of Winslow, including the Ruby Wash Diversion Levee, and portions of unincorporated Navajo County. Alternatives include various combinations of structural and non-structural measures such as reconstruction of portions of the existing Winslow Levee and Ruby Wash Diversion Levee, levee setbacks, flood warning system and elevation of residential structures, and river channel conveyance improvements. The IFR evaluates the No Action Alternative and ten action alternatives, Alternatives 1.1, 3.1, 7, 8, 9, 10, 10.1, 10.2, 10.3, and 10.4, in detail. The tentatively selected plan is Alternative 10.1. The official closing date for the receipt of comments is 45 days from the date on which the Environmental Protection Agency publishes the Notice of Availability of this Draft IFR in the Federal Register. Comments should be addressed to: Eduardo T. De Mesa; Chief, Planning Division; U.S. Army Corps of Engineers; Los Angeles District; 915 Wilshire Blvd., Suite 930 ATTN: Kirk Brus, Environmental Coordinator Los Angeles, California 90017 Comments or requests for further information may also be emailed to: [email protected] For further information, you may contact: Mr. Richard Legere, Lead Planner, Phone: 602-230-6907; Or Mr. Kirk Brus, Environmental Coordinator, Phone: 213-452-3876 Mailing address and email address listed above. This page left blank for duplex printing Contents EXECUTIVE SUMMARY ................................................................................................................... ES-I 1.0 STUDY INFORMATION ................................................................................................................... 1-1 1.1. Study Authority ............................................................................................................................ 1-1 1.2. Study Purpose and Scope ............................................................................................................. 1-1 1.3. Study Area and Location .............................................................................................................. 1-1 1.3.1. Study General Location ........................................................................................................ 1-1 1.3.2. Study Area ............................................................................................................................ 1-2 1.4. History of the Study ..................................................................................................................... 1-2 1.5. Prior Reports and Existing Projects .............................................................................................. 1-5 1.6. Planning Process and Report Organization .................................................................................. 1-5 1.6.1. Planning Process .................................................................................................................. 1-5 1.6.2. Report Organization ............................................................................................................. 1-7 2.0 PURPOSE AND NEED * ................................................................................................................... 2-1 2.1. Statement of Need ........................................................................................................................ 2-1 2.2. Statement of Purpose .................................................................................................................... 2-2 2.3. National Objectives ...................................................................................................................... 2-2 2.4. Public Concerns ............................................................................................................................ 2-3 2.5. Problems and Opportunities ......................................................................................................... 2-3 2.5.1. Problems ............................................................................................................................... 2-3 2.5.2. Opportunities ........................................................................................................................ 2-3 2.6. Planning Objectives ...................................................................................................................... 2-4 2.7. Planning Constraints..................................................................................................................... 2-4 3.0 PLAN FORMULATION..................................................................................................................... 3-1 3.1. Plan Formulation Strategy ............................................................................................................ 3-1 3.2. Planning Process Initial Array ...................................................................................................... 3-1 3.2.1. Management Measures ......................................................................................................... 3-2 3.2.2. Measures Eliminated from Further Consideration ............................................................... 3-2 3.2.3. Preliminary Alternatives ...................................................................................................... 3-4 3.2.4. Preliminary Cost Estimates .................................................................................................. 3-7 3.3. Alternative Evaluation and Comparison ...................................................................................... 3-7 3.3.1. Alternatives Eliminated from Further Study ........................................................................ 3-8 3.4. Focused Array of Alternatives...................................................................................................... 3-9 3.4.1. Refinement of Alternatives .................................................................................................. 3-9 3.4.2. Development of Alternatives 8, 9 and 10 ........................................................................... 3-11 3.4.3. Final Array of Alternatives ................................................................................................ 3-12 3.4.4. Operation and Maintenance Requirements for all Alternatives ......................................... 3-42 3.4.5. Proposed Project Area ........................................................................................................ 3-43 3.4.6. Analysis of Focused Array ................................................................................................. 3-55 3.4.7. Without-Project Conditions................................................................................................ 3-56 i Little Colorado River, Winslow, Arizona May 2016 3.4.8. Without Project Condition - Life Safety ............................................................................ 3-58 3.4.9. NED Benefit, Costs and Residual Damages. ..................................................................... 3-66 3.4.10. Incremental Evaluation and Justification ........................................................................... 3-68 3.4.11. Alternative Scale Optimization .......................................................................................... 3-68 3.5. NED Net Benefit Evaluation ...................................................................................................... 3-69 3.5.1. Life Safety—Comparison among Alternatives .................................................................. 3-70 3.6. System of Accounts .................................................................................................................... 3-76 3.6.1. National Economic Development ...................................................................................... 3-76 3.6.2. Environmental Quality ....................................................................................................... 3-76 3.6.3. Regional Economic Development ...................................................................................... 3-78 3.6.4. Other Social