FLOODPLAIN MANAGEMENT PLAN COUNTY OF SAN DIEGO, CALIFORNIA Prepared for: Region IX August 2007 County of San Diego Table of Contents Floodplain Management Plan August 2007 Page i TABLE OF CONTENTS TABLE OF CONTENTS..............................................................................................................................I LIST OF ACRONYMS................................................................................................................................V EXECUTIVE SUMMARY ...................................................................................................................... VII 1.0 INTRODUCTION........................................................................................................................ 1-1 1.1 PURPOSE AND SCOPE OF THIS DOCUMENT..................................................................... 1-1 1.2 THE FMP AND THE COMMUNITY RATING SYSTEM..................................................................... 1-1 1.3 GOALS OF THE FMP.................................................................................................................... 1-2 1.4 ORGANIZATION OF THE PLAN ..................................................................................................... 1-3 2.0 COUNTY PROFILE.................................................................................................................... 2-1 2.1 GEOGRAPHY, DEMOGRAPHICS, AND CLIMATE............................................................. 2-1 2.2 PLANNING AREA.......................................................................................................................... 2-2 2.3 INFRASTRUCTURE ....................................................................................................................... 2-3 2.4 HYDROLOGY ............................................................................................................................... 2-3 2.5 WATERSHEDS ............................................................................................................................. 2-5 2.5.1. Otay River Watershed ....................................................................................................... 2-5 2.5.2. San Luis Rey Watershed ................................................................................................... 2-6 2.5.3. Santa Margarita Watershed ............................................................................................... 2-6 2.5.4. San Dieguito Watershed.................................................................................................... 2-7 2.5.5. Sweetwater River Watershed ............................................................................................ 2-7 2.5.6. San Diego Watershed........................................................................................................ 2-7 2.5.7. Tijuana Watershed............................................................................................................. 2-8 2.6 DEVELOPMENT TRENDS.............................................................................................................. 2-8 3.0 PLANNING PROCESS AND PUBLIC PARTICIPATION .................................................... 3-1 3.1 BACKGROUND ............................................................................................................................ 3-1 3.2 FMP WORKING GROUP .............................................................................................................. 3-1 3.3 PUBLIC INVOLVEMENT ............................................................................................................... 3-2 3.3.1 Press Release ......................................................................................................................... 3-2 3.3.2 Repetitive Loss Property Owners and Lessee Mailings......................................................... 3-2 3.3.3 Public Meeting....................................................................................................................... 3-3 3.3.4 Repetitive Loss Neighborhood Mailings ............................................................................... 3-3 3.3.5 Federal, State, Local, and Regional Agencies/organizations Survey..................................... 3-3 3.3.6 Survey of Adjacent Municipalities ........................................................................................ 3-4 3.4 PUBLIC COMMENTS..................................................................................................................... 3-5 3.5 EXISTING PLANS OR STUDIES REVIEWED....................................................................... 3-9 4.0 FLOODING HISTORY............................................................................................................... 4-1 5.0 FLOOD HAZARD IDENTIFICATION AND RISK ASSESSMENT..................................... 5-1 5.1 DEFINITION OF FLOOD......................................................................................................... 5-1 5.2 FLOOD HAZARD RISK................................................................................................................ 5-2 5.3 FLOOD INSURANCE RATE MAPS AND THE COUNTY OF SAN DIEGO FLOOD MAPS....................... 5-5 5.4 LOCALLY IDENTIFIED “HOT SPOT” FLOOD AREAS ..................................................................... 5-5 5.5 VULNERABLE STRUCTURES ........................................................................................................ 5-8 5.6 LOSS ESTIMATES ...................................................................................................................... 5-11 County of San Diego Table of Contents Floodplain Management Plan August 2007 Page ii 6.0 CAPABILITIES ASSESSMENT................................................................................................ 6-1 6.1 GOVERNMENT STRUCTURE......................................................................................................... 6-1 6.2 COUNTY FACILITIES ................................................................................................................... 6-1 6.3 FLOODPLAIN MANAGEMENT PROGRAM...................................................................................... 6-2 6.4 OPERATION AND MAINTENANCE PROGRAM................................................................................ 6-2 6.5 DAM SAFETY .............................................................................................................................. 6-3 6.6 DEBRIS CONTROL PROGRAM ...................................................................................................... 6-3 6.7 EMERGENCY STORM RESPONSE.................................................................................................. 6-3 6.9 ALERT FLOOD WARNING SYSTEM ............................................................................................. 6-3 7.0 GOALS AND OBJECTIVES ...................................................................................................... 7-1 8.0 PREVENTION MEASURES ...................................................................................................... 8-1 8.1 CURRENT PREVENTION MEASURES .............................................................................................. 8-1 8.1.1 General plan........................................................................................................................... 8-1 8.1.2 Zoning.................................................................................................................................... 8-3 8.1.3 Building Codes ...................................................................................................................... 8-4 8.1.4 Floodplain Construction Standards........................................................................................ 8-5 8.1.5 Alluvial Fan Regulations ....................................................................................................... 8-7 8.1.6 Floodplain Mapping/Data Maintenance ................................................................................ 8-9 8.1.7 Floodplain Open Space Preservation..................................................................................... 8-9 8.1.8 Low-Density Zoning............................................................................................................ 8-10 8.1.9 Subdivision Regulations ...................................................................................................... 8-11 8.2 PROPOSED PREVENTION MEASURES IN SAN DIEGO COUNTY.................................................... 8-12 8.2.1 Design/Regulatory Flood Elevation (Freeboard)................................................................. 8-12 8.2.2 Cumulative Substantial Improvement and Substantial Damage Regulations..................... 8-13 8.2.3 Critical Facilities Regulations.............................................................................................. 8-15 9.0 PROPERTY PROTECTION ...................................................................................................... 9-1 9.1 ACQUISITION AND DEMOLITION ................................................................................................. 9-1 9.1.1 Implementation Policies ........................................................................................................ 9-1 9.1.2 Acquisition Disadvantages ...................................................................................................