Natural Hazards Mitigation Plan Section 7 – Floods City of Newport Beach, California SECTION 7: FLOODS Table of Contents Why Are Floods a Threat to the City of Newport Beach? ............................ 7-1 History of Flooding in the City of Newport Beach ............................................................... 7-3 Historic Flooding in Orange County .......................................................................................... 7-8 Historic Flooding in Southern California ................................................................................. 7-11 What Factors Create Flood Risk? ................................................................... 7-14 Climate ........................................................................................................................................... 7-14 Tides ................................................................................................................................................ 7-19 Geography and Geology .............................................................................................................. 7-20 Built Environment ......................................................................................................................... 7-21 How Are Flood-Prone Areas Identified? ....................................................... 7-21 Flood Mapping Methods and Techniques ................................................................................ 7-22 Flood Terminology ....................................................................................................................... 7-23 Floodplain .......................................................................................................................................................... 7-23 100-Year Flood ................................................................................................................................................ 7-23 Floodway ............................................................................................................................................................ 7-23 Flood Fringe ...................................................................................................................................................... 7-23 Development .................................................................................................................................................... 7-24 Base Flood Elevation (BFE) .......................................................................................................................... 7-24 Storm Flooding Characteristics ................................................................................................. 7-24 Riverine Flooding ............................................................................................................................................. 7-24 Urban Flooding ................................................................................................................................................ 7-24 Debris Flows ..................................................................................................................................................... 7-25 Coastal Flooding .............................................................................................................................................. 7-25 Tsunami and Rogue Wave Flooding ............................................................... 7-26 Notable Tsunamis and Rogue Waves in the Newport Beach Area ................................................. 7-27 Santa Barbara Tsunami of 1812 ............................................................................................................... 7-30 Tsunami of January 1927 ............................................................................................................................ 7-31 Possible Tsunami of 1934 ............................................................................................................................ 7-31 Aleutian Island Tsunami of 1957 .............................................................................................................. 7-31 Chilean Tsunami of 1960 ............................................................................................................................ 7-31 Good Friday Earthquake Tsunami of 1964 ............................................................................................ 7-32 Chilean Tsunami of February 2010 .......................................................................................................... 7-32 Tohoku-oki Tsunami of March 2011 ....................................................................................................... 7-32 Seismically Induced Inundation ....................................................................... 7-32 Dam Failure Flooding ................................................................................................................... 7-32 Flooding Due to Failure of Above-Ground Water Storage Tanks .................................... 7-34 Flooding Due to Sea Level Rise ....................................................................... 7-35 Sea Level Change .......................................................................................................................... 7-35 2014 PAGE 7- i Natural Hazards Mitigation Plan Section 7 – Floods City of Newport Beach, California Effects of Sea Level Rise .............................................................................................................. 7-38 Hazard Assessment .......................................................................................... 7-38 Hazard Identification – Flood Hazard Mapping in Newport Beach ................................... 7-38 Inundation Due to Storm Flooding ............................................................................................................. 7-39 Inundation Due to Tsunami and Rogue Waves..................................................................................... 7-40 Inundation Due to Catastrophic Failure of Water Storage Structures ............................................ 7-45 Inundation Due to Hurricanes and Tropical Storms ............................................................................ 7-53 Inundation Due to Sea Level Rise .............................................................................................................. 7-54 Vulnerability Assessment – Community Flood Issues .................................. 7-55 What is Susceptible to Damage During a Flood Event? ....................................................... 7-55 Risk Analysis ..................................................................................................... 7-56 General Building Stock Exposure and Potential Building-Related Losses ........................................ 7-56 Shelter Requirements .................................................................................................................................... 7-57 Expected Damage to Essential Facilities .................................................................................................. 7-57 Business/Industry ............................................................................................................................................. 7-58 Public Infrastructure ....................................................................................................................................... 7-58 Water Quality .................................................................................................................................................. 7-61 Current Flood Mitigation Activities ............................................................... 7-61 Studies Prior to Development ...................................................................................................................... 7-61 Acquisition and Protection of Open Space in the Floodplain .............................................................. 7-61 Improvements to the Water District’s Infrastructure ........................................................................... 7-61 Stormwater Systems and Surface Water Quality ................................................................................. 7-62 Tsunami Evacuation System ........................................................................................................................ 7-63 Potential Human Actions in Response to Sea Level Change .............................................................. 7-63 Flood Resource Directory ............................................................................... 7-64 County and Local Resources .................................................................................................... 7-64 State Resources ............................................................................................................................ 7-64 Federal Resources and Programs ............................................................................................. 7-65 Other National Resources ........................................................................................................ 7-66 Publications ................................................................................................................................... 7-68 2014 PAGE 7- ii Natural Hazards Mitigation Plan Section 7