WILLIAMSON COUNTY Interjurisdictional Community Flood Protection Plan Office of Emergency Management 911 Tracy Chambers Lane | Georgetown, TX 78626 Phone: 512.943.19 Table of Contents WILLIAMSON COUNTY Interjurisdictional Community Flood Protection Plan TABLE OF CONTENTS Acknowledgments ............................................................................................................. vi Executive Summary .......................................................................................................... vii Chapter 1. Introduction .................................................................................................. 1-1 1.1 Why Prepare This Plan? .......................................................................................... 1-1 Chapter 2. Plan Development Methodology ............................................................ 2-1 2.1 Defining the Planning Area ..................................................................................... 2-1 2.2 The Process ............................................................................................................. 2-2 2.3 Coordination with Other Agencies ......................................................................... 2-3 2.4 Review of Existing Programs ................................................................................... 2-3 2.5 Public Involvement ................................................................................................. 2-4 Chapter 3. Williamson County Profile ........................................................................ 3-1 3.1 Historical Overview ................................................................................................. 3-1 3.2 Physical Setting ....................................................................................................... 3-1 3.3 Geography ............................................................................................................... 3-2 3.4 Climate .................................................................................................................... 3-3 3.5 Development Features ........................................................................................... 3-5 3.6 Demographics ......................................................................................................... 3-7 3.7 Economy.................................................................................................................. 3-9 3.8 Watersheds ............................................................................................................. 3-9 Chapter 4. Relevant Programs and Regulations ...................................................... 4-1 4.1 Federal .................................................................................................................... 4-1 4.2 State ........................................................................................................................ 4-7 4.3 Local ...................................................................................................................... 4-10 4.4 Capability Assessment .......................................................................................... 4-11 Chapter 5. Risk Assessment Overview ....................................................................... 5-1 5.1 Purpose of Risk Assessment.................................................................................... 5-1 5.2 Methodology ........................................................................................................... 5-1 Chapter 6. Risk Assessment Implementation ........................................................... 6-1 6.1 General Concepts .................................................................................................... 6-1 6.2 Defining Flood Hazards ........................................................................................... 6-2 6.3 Major Flood Events ................................................................................................. 6-3 Chapter 7. Flood Hazard Exposure ............................................................................. 7-1 7.1 Land Use in the Floodplain...................................................................................... 7-1 iii WILLIAMSON COUNTY Table of Contents Interjurisdictional Community Flood Protection Plan 7.2 Critical Facilities and Infrastructure ........................................................................ 7-1 Chapter 8. Flood Hazard Vulnerability ....................................................................... 8-1 8.1 Vulnerable Populations ........................................................................................... 8-1 8.2 Impacts on Property ............................................................................................... 8-1 Chapter 9. Mitigation Strategy .................................................................................... 9-1 9.1 Mission Statement, Goals and Objectives .............................................................. 9-1 9.2 Catalog of Mitigation Alternatives .......................................................................... 9-1 Chapter 10. Action Plan Development ....................................................................... 10-1 10.1 Building a Mitigation Strategy .............................................................................. 10-1 10.2 Identifying projects to reduce risk ........................................................................ 10-3 Chapter 11. Plan Maintenance ...................................................................................... 11-1 11.1 Plan implementation ............................................................................................ 11-1 11.2 Steering Committee .............................................................................................. 11-1 11.3 Annual Progress Report ........................................................................................ 11-2 11.4 Plan Update ........................................................................................................... 11-2 11.5 Continuing Public Involvement ............................................................................. 11-3 11.6 Incorporation into Other Planning Mechanisms .................................................. 11-3 Chapter 12. Glossary of Terms ..................................................................................... 12-1 12.1 Acronyms .............................................................................................................. 12-1 12.2 Definitions ............................................................................................................. 12-3 Tables Table 1-1. Community FIRM Data ..................................................................................................................................... 1-8 Table 2-1. Williamson County CFPP Core Committee Members ...................................................................................... 2-3 Table 3-1. Williamson County Geography ......................................................................................................................... 3-1 Table 3-2. Average Weather Georgetown, TX - 78628 - 1981-2010 Averages ................................................................. 3-3 Table 3-3. Recent Population Data .................................................................................................................................... 3-7 Table 4-1. NFIP Participation by Williamson County and Municipalities.......................................................................... 4-1 Table 4-2. Williamson County and Municipalities Legal and Regulatory Capability ...................................................... 4-11 Table 5-1. Number of Structures by Flood Depth by Municipality ................................................................................... 5-4 Table 5-2. Number of Structures by Flood Depth by Watershed ..................................................................................... 5-5 Table 5-3. Improvement Market Value by Municipality ................................................................................................... 5-6 Table 5-4. Improvement Market Value by HUC 12 Watershed ............................................................................................ 5-6 Table 7-1. Land Use in the Floodplain ............................................................................................................................... 7-1 Table 7-2. Critical Facilities and Infrastructure in the 500-year Floodplain ..................................................................... 7-2 Table 7-3. Dam Counts and Exemptions ........................................................................................................................... 7-7 Table 8-1. USACE Generic Damage Functions, Structure.................................................................................................. 8-2 Table 8-2. USACE Generic Damage Functions, Contents .................................................................................................. 8-2 Table 8-3. Watershed Prioritization Exercise .................................................................................................................... 8-4 Table 10-1. Williamson County Hazard Mitigation Plan Flood Mitigation Actions .......................................................