2017 Ada County Multi-Hazard Mitigation Plan: Volume 1—Countywide Elements August 2017 PREPARED FOR PREPARED BY Ada County Emergency Management Tetra Tech 7200 Barrister Drive Phone: 208-577-4750 90 South Blackwood Avenue Phone: 208.939.4391 Boise ID 83704-9293 Fax: 208-577-4759 Eagle, ID 83616 Fax: 208.939.4402 www.adaprepare.id.gov tetratech.com Tetra Tech Project #103S3856 \\IWRS065FS1\Data\Active\0_HazMitigation\103s3856.emi_AdaCountyHMPUpdate\2017-08_ApprovedFinal\2017_AdaCoHazMitPlanVol1_Final_2017-08- 31.docx 2017 Ada County Multi-Hazard Mitigation Plan: Volume 1—Countywide Elements Contents CONTENTS Executive Summary ............................................................................................................. xiii Part 1. Background and Methods ........................................................................................ 1-1 1. Introduction to the Planning Process ........................................................................................................... 1-1 1.1 Why Prepare This Plan? ...................................................................................................................... 1-1 1.2 Who Will Benefit From This Plan? ..................................................................................................... 1-2 1.3 How to Use This Plan .......................................................................................................................... 1-2 2. Plan Update—What Has Changed? ............................................................................................................. 2-1 2.1 Previous Plans ..................................................................................................................................... 2-1 2.2 Progress Reporting .............................................................................................................................. 2-2 2.3 Why Update? ....................................................................................................................................... 2-2 2.4 The Updated Plan—What Is Different? .............................................................................................. 2-2 3. Plan Methodology ........................................................................................................................................ 3-1 3.1 Grant Funding ...................................................................................................................................... 3-1 3.2 Formation of the Planning Team ......................................................................................................... 3-1 3.3 Establishment of the Planning Partnership .......................................................................................... 3-1 3.4 Defining the Planning Area ................................................................................................................. 3-2 3.5 The Steering Committee ...................................................................................................................... 3-2 3.6 Coordination with Other Agencies ...................................................................................................... 3-4 3.7 Review of Existing Programs .............................................................................................................. 3-5 3.8 Public Involvement .............................................................................................................................. 3-6 3.9 Plan Development Chronology/Milestones ....................................................................................... 3-12 4. Ada County Profile ...................................................................................................................................... 4-1 4.1 Jurisdictions and Attractions ............................................................................................................... 4-1 4.2 Historical Overview............................................................................................................................. 4-2 4.3 Major Past Hazard Events ................................................................................................................... 4-3 4.4 Physical Setting ................................................................................................................................... 4-4 4.5 Development ....................................................................................................................................... 4-5 4.6 Demographics .................................................................................................................................... 4-15 4.7 Economy ............................................................................................................................................ 4-19 4.8 Laws, Ordinances and programs ....................................................................................................... 4-22 5. Hazards of Concern for Risk Assessment .................................................................................................... 5-1 6. Risk Assessment Methodology .................................................................................................................... 6-1 Part 2. Risk Assessment ...................................................................................................... 6-1 7. Dam/Canal Failure ....................................................................................................................................... 7-1 7.1 General Background ............................................................................................................................ 7-1 7.2 Hazard Profile ...................................................................................................................................... 7-4 7.3 Secondary Hazards .............................................................................................................................. 7-9 7.4 Exposure .............................................................................................................................................. 7-9 7.5 Vulnerability ...................................................................................................................................... 7-11 7.6 Development Trends ......................................................................................................................... 7-12 7.7 Scenario ............................................................................................................................................. 7-13 7.8 Issues ................................................................................................................................................. 7-13 8. Drought ........................................................................................................................................................ 8-1 8.1 General Background ............................................................................................................................ 8-1 v 2017 Ada County Multi-Hazard Mitigation Plan: Volume 1—Countywide Elements Contents 8.2 Hazard Profile ...................................................................................................................................... 8-5 8.3 Secondary Hazards .............................................................................................................................. 8-6 8.4 Exposure .............................................................................................................................................. 8-6 8.5 Vulnerability ........................................................................................................................................ 8-6 8.6 Development Trends ........................................................................................................................... 8-7 8.7 Scenario ............................................................................................................................................... 8-8 8.8 Issues ................................................................................................................................................... 8-8 9. Earthquake ................................................................................................................................................... 9-1 9.1 General Background ............................................................................................................................ 9-1 9.2 Hazard Profile ...................................................................................................................................... 9-6 9.3 Secondary Hazards ............................................................................................................................ 9-15 9.4 Exposure ............................................................................................................................................ 9-15 9.5 Vulnerability ...................................................................................................................................... 9-17 9.6 Development Trends ......................................................................................................................... 9-20 9.7 Scenario ............................................................................................................................................