Rancho Santiago Community College District SECTION IV-C FLOOD/STORM TABLE OF CONTENTS A. THE CALIFORNIA FLOOD THREAT ......................................................................... 5 Figure 1 - California Aqueducts, Canals and Natural Hydrologic Regions ................................................. 5 CALIFORNIA FLOOD HAZARDS ...................................................................................... 6 CALIFORNIA FLOOD HISTORY ....................................................................................... 7 Table 1 - California Flood Disasters 1992-2010 ....................................................................................... 7 Figure 2 - State/Federal Floods 1950-2009 ............................................................................................... 7 Figure 3 - FEMA Flood Insurance Rate Map Flood Zone Designation ...................................................... 8 Table 2 - FEMA FIRM Descriptions .......................................................................................................... 9 Table 3 - Counties with 100,000+ People Living in Floodplain, 2000 ..................................................... 10 Table 4 - Historic Damage Claims and Repetitive Loss Payments from 1992 to 2002 ........................... 10 PARTICIPATION IN THE NATIONAL FLOOD INSURANCE PROGRAM (NFIP) ....................... 11 SOUTH COAST HYDROLOGIC REGION .......................................................................... 12 LOCAL GOVERNMENTS ............................................................................................... 12 B. THE ORANGE COUNTY FLOOD THREAT .............................................................. 12 Figure 4 - Watersheds of Orange County .................................................................................. 13 ORANGE COUNTY FLOOD THREAT............................................................................... 14 Figure 5: Orange County Rivers and Creeks ........................................................................................... 15 FACTORS CREATING FLOOD RISK ............................................................................... 20 Table 5 - Tropical Storms that Affected Southern California in the 20th Century ................................... 21 FLOOD TERMINOLOGY ................................................................................................ 23 CHARACTERISTICS OF FLOODING ................................................................................ 25 C. ORANGE COUNTY FLOOD CONTROL DISTRICT (OCFCD) .................................... 27 IDENTIFICATION OF ORANGE COUNTY FLOOD-PRONE AREAS ....................................... 28 Figure 6 - 100-Year Floodplain in Orange County ................................................................................... 29 Figure 7 - FEMA Q3 Flood Data for Orange County ................................................................................ 30 FLOOD COMMUNITY IMPACT........................................................................................ 31 SANTA ANA RIVER HAZARD MITIGATION PROJECT ...................................................... 34 Figure 8 - Santa Ana River Mainstem Project .......................................................................................... 36 D. ORANGE COUNTY HAZUS FLOOD STUDY ............................................................ 37 HAZUS FLOOD LOSS ESTIMATION MODEL ................................................................... 37 Rancho Santiago Community College District GENERAL BUILDING STOCK ........................................................................................ 37 Table 6 – Building Exposure by Occupancy Type for Study Region & Scenario .................................... 38 Table 7 - Expected Building Damage by Occupancy and Building Type ................................................ 39 Figure 9 - Orange County Levee System Protected Areas ...................................................................... 40 SCENARIO #1 - 100-YEAR FLOOD (LEVEES INTACT) ..................................................... 41 Table 8 - Summary of Impacts due to 100-Year Flood (Levees Intact) .................................................. 41 Figure 10 – 100-Year Flood Event Floodplain and Depth Grid ................................................................ 41 Table 9 - Impacts OC School Districts 100-Year Flood (Levees Intact) .................................................. 42 Figure 11 - OC School Districts Functionality – 100-Year Flood (Levees Intact) ..................................... 43 SCENARIO 2 – 100-YEAR (WITHOUT LEVEES) ............................................................... 44 Table 10 - Summary Impacts for OC due to a 100-Year Flood ............................................................... 44 Figure 12 - Total Direct Economic Loss – 100-Year Flood ...................................................................... 44 Table 11 - Essential Facility Loss Estimates – 100-Year Flood .............................................................. 45 Table 12 - Impacts on OC Schools Districts – 100-Year Flood ............................................................... 46 Figure 13 - OC School Districts Functionality following – 100-Year Flood ............................................... 47 SCENARIO #3 – 500-YEAR FLOOD (WITHOUT LEVEES) ................................................. 48 Table 13 - Summary Impacts for 500-Year Flood (Levees Intact) .......................................................... 48 Figure 14 - Total Direct Economic Loss 500-Year Flood ......................................................................... 48 Table 14 - Impacts on OC School Districts - 500-Year Flood (Levees Intact)......................................... 49 Figure 15 - School Districts Functionality following – 500-Year (Levees Intact) ...................................... 50 Table 15 - Summary of Impacts on Orange County for Three Flood Scenarios ..................................... 50 E. THE RSCCD FLOOD THREAT STUDY BY MMI ENGINEERING ................................ 51 Table 16: RSCCD Flood History ............................................................................................................ 51 Table 17: Summary of RSCCD Building Data Considered in the Study ................................................. 52 Figure 16: FEMA Flood Hazard Zones for Orange County ...................................................................... 53 Figure 17: FEMA Flood Hazard Zones for RSCCD Facilities .................................................................. 54 Table 18: Summary of RSCCD Building Exposure to Mapped Flood Hazards ....................................... 55 Table 19: RSCCD Site Impact Results .................................................................................................. 55 Figure 18: HAZUS Estimated Flood Depths for the Orange County 100-Year Flood .............................. 57 Figure 19: HAZUS-Estimated Flood Depths for the 100-Year Flood in Vicinity of RSCCD Facilities ...... 58 Figure 20: HAZUS Flood Depths for Orange County for the 500-Year Flood .......................................... 59 Figure 21: HAZUS-Estimated Flood Depths for 500-Year Flood in the Vicinity of RSCCD Facilities ...... 60 BUILDING CLASSIFICATION FOR RISK ASSESSMENT ..................................................... 61 Table 20: Assumed First Floor Heights for Selected Buildings ............................................................... 62 FLOOD RISK ASSESSMENT RESULTS .......................................................................... 63 Table 21: Summary of Economic Impacts from Flooding for RSCCD Facilities by Site .......................... 64 Figure 22: Santa Ana College for 100-Year Flood- Building and Content Damage Distributions ............ 65 Figure 23: Centennial Ed. Center 100-Year Flood -Building & Content Damage Distributions ................ 68 Figure 24: Santa Ana College for 500-Year Flood - Building and Content Damage Distributions ........... 69 Figure 25: A Centennial Ed. Center 500-Year Flood-Building and Content Damage Distributions .......... 70 Figure 26: District Office for the 500-Year Flood - Building and Content Damage Distributions .............. 71 Table 22: Buildings Predicted by HAZUS to Suffer Damage in 100-Year or 500-Year Flood ................. 72 MMI ENGINEERING STUDY CONCLUSIONS AND RECOMMENDATIONS ............................. 73 F. THE LOCALIZED FLOODING ISSUES .................................................................... 73 IV-C. Flood/Storm Page 2 of 77 Rancho Santiago Community College District Table 23: RSCCD Elevation by Site ....................................................................................................... 74 G. FLOOD PROBABILITY OF FUTURE OCCURRENCES ................................................ 75 Table 24: Probability for Flood Scenarios .............................................................................................. 75 H. FLOOD/STORM HAZARD MITIGATION STRATEGIES ............................................... 76 SHORT TERM MITIGATION STRATEGIES ....................................................................... 76 FLOOD ACTIVITY #1 – SHORT TERM ............................................................................................... 76 Buildings Predicted by HAZUS to Suffer Damage in 100-Year or 500-Year Flood .................................. 77