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<br /> Hazard Mitigation Plan | 2022 <br />Flood Hazards <br />- 72 - <br /> <br />Q&A | ELEMENT B: HAZARD IDENTIFICATION AND RISK ASSESSMENT | B2a. <br />Q: Does the plan include information on previous occurrences of hazard events for each jurisdiction? <br />(Requirement §201.6(c)(2)(i)) <br />A: See Previous Occurrences of Flooding in the City below. <br /> <br />Previous Occurrences of Flooding in the City <br />According to the NOAA Storm Events Database, the most recent flooding event to occur within <br />the City was on December 6, 2018. A moisture plume with a weak atmospheric river arrived on <br />December 5th and brought rain to the region. On December 6th, a strong closed upper level low <br />pressure brought an unstable air mass into Southern California with showers and thunderstorms, <br />especially Orange and San Diego Counties. Rainfall of 1 <br />inch per hour amounts occurred in Costa Mesa as well as <br />adjacent cities. The main storm system on December 6th <br />brought widespread rain to the entire region. All <br />mountains and the coast and valleys areas received 1-3 <br />inches and some spots receiving over 4 of rainfall over <br />higher terrain. The most significant mud and debris flows <br />occurred at recent Holy burn scar areas, and many reports <br />of flash flooding across the region. Snow fell as low as <br />4000 feet with mountains receiving 1 to 4 inches of snow. <br />John Wayne Airport reported 2.56 inches of rainfall in <br />about 2 hours on December 6th. This is a 1 in 100 year <br />return interval. Cars in nearby Costa Mesa were seen <br />completely submerged or stalled in deep water up to the <br />windows. <br /> <br />Orange County has experienced the following flood events <br />since 2018: <br /> <br />Table: Flooding and Flash Flooding Events in Orange County <br />Source: NOAA Storm Events Database: <br />Date Location <br />04/06/2020 Peralta Hills <br />04/06/2020 Costa Mesa <br />04/06/2020 Los Alamitos <br />04/06/2020 Cypress <br />11/28/2019 Huntington Beach <br />11/19/2019 San Clemente <br />05/22/2019 Fullerton <br />03/06/2019 Freeway <br />02/13/2019 Laguna Beach <br />02/04/2019 Arcilla <br />01/15/2019 Seal Beach <br />12/06/2018 San Clemente <br />12/06/2018 Esperanza <br />12/06/2018 Anaheim <br />12/06/2018 Santa Ana <br />01/09/2018 San Clemente