Together with the County of San Diego, the City of Encinitas has identified the hazards below as the top six, based on their probability and potential impact.
To mitigate the impact of these potential hazards, the County has created the Multi-Jurisdictional Hazard Mitigation Plan (Plan). The Plan is updated every five years. In 2014, community input from the entire County was solicited to update and improve the 2015 Plan Update. The update can be found here.
On November 22, 1800, a 6.5 magnitude occurred on the Rose Canyon fault offshore from Oceanside. It cracked adobe walls at the missions of San Diego de Alcala and San Juan Capistrano. Other notable local earthquakes include a magnitude 6.0 earthquake centered on the Rose Canyon or Coronado Band faults on May 27, 1862, and a magnitude 5.4 earthquake centered off the coast of Oceanside on the Coronado Bank Fault on July 13, 1986. The geographic extent of this hazard is citywide. A greater percentage of the city’s population is potentially exposed to this hazard relative to other hazards, and potential losses from an earthquake would be comparatively larger in most cases.
The Rose Canyon Fault lies offshore (2.5 miles west of the city at its closest point) and is capable of generating a magnitude 6.2 to 7.2 earthquake that could potentially damage dwellings and infrastructure throughout the city. A magnitude 6.9 earthquake on the Rose Canyon Fault could potentially result in a peak ground acceleration of .40 within downtown Encinitas and the Coast Highway 101 corridor. These areas of the city are more likely to suffer heavier damage and greater human losses than other parts of the city because of the presence of older buildings (including 19 unreinforced masonry buildings and several multi-unit buildings constructed prior to 1973), a relatively higher population density and softer soils susceptible to liquefaction, lurch cracking, lateral spreading and local subsidence.
A significant number of Encinitas residents live within the wildland-urban interface. The geographic extent of this hazard includes the following areas of the city, for the most part: 1) Saxony Canyon; 2) South El Camino Real/Crest Drive; and 3) Olivenhain. Properties in these and other smaller areas are susceptible to wildfire because they are situated near open space and canyons containing heavy fuel loads. Reoccurring periods of low precipitation have increased the risk of wildfires in the region. A greater percentage of the population is potentially exposed to wildfires. Potential losses from this hazard are comparatively larger than those associated with a dam failure, flooding, coastal bluff failures or hazardous material incidents. Recent wildfire events in Encinitas include a wildfire in the central part of the city in 1970 and three wildfires in the community of Olivenhain in 1943, 1980 and 1996. The 1996 Harmony Grove Fire resulted in the loss of three homes and the evacuation and sheltering of hundreds of residents.
Geologists estimate that a magnitude 7.5 earthquake from the Elsinore Fault, located 11 miles east of Lake Wohlford, could result in a failure of its hydraulic fill dam. The geographic extent of this hazard is limited to the persons and properties within the inundation path surrounding Escondido Creek and San Elijo Lagoon. The dam inundation path is larger than the Escondido Creek 100-year floodway and a greater number of persons and properties are exposed to this hazard compared to coastal bluff failures and flooding. Major arterials within the inundation path include El Camino Del Norte, Rancho Santa Fe Road, Manchester Avenue and Coast Highway 101. The failure of Wohlford Dam (1895) and Dixon Reservoir Dam (1970) could possibly threaten city facilities and infrastructure (including the San Elijo Water Reclamation Facility, Cardiff and Olivenhain sewer pump stations and the San Dieguito Water District 36” high pressure supply line) and educational facilities (Mira Costa College) located in and adjacent to the inundation path. Although exposure to loss of property is significant, the potential for loss of life is limited because of the length of time before flood wave arrival (approximately 1 ½ hours) allowing for aggressive warning and evacuation measures to be initiated by the city.
The Olivenhain Dam (2003) is a concrete gravity dam located on a tributary of Escondido Creek, just west of Lake Hodges, holding 24,000 acre feet. Stanley Mahr Reservoir (1981) is a small, earth-filled embankment dam located on a tributary of Encinitas Creek in San Marcos with a capacity of approximately 200 acre feet. A failure of Mahr Reservoir in Carlsbad would produce flooding along Encinitas Creek (which flows into Batiquitos Lagoon) in the northern portion of the city. Emergency Action Plans have been developed for these dams. The risk of failure of both dams is relatively low due to their age and construction and existing surveillance and inspection measures.
Coastal Bluff Failures
Geographic extent of the hazard is limited primarily to the Encinitas coastal sandstone bluffs. After the El Niño storms of 1982-1983, Encinitas beaches were stripped of vertical sand up to 20 feet deep, putting the coastal bluffs and homes in jeopardy of collapsing into the sea. Furthermore, the shoreline segments at Moonlight Beach and Cardiff-by-the-Sea are extremely vulnerable to coastal inundation from potential future sea level rise. In 2000, unstable cliffs at Beacon’s Beach in Encinitas caused a landslide that killed a woman sitting on the beach. The recreational bicycle path along the seaside of Highway 101 was undermined in 2010.
Erosion studies have been conducted for Encinitas, Solana Beach and Del Mar. Various degrees of coastal bluff erosion occur annually and coastal bluff failures have resulted in limited loss of life. As a result, negotiations with the California Coastal Commission are underway to develop a comprehensive coastal bluff policy towards coastal bluff top development. A smaller percentage of the population is exposed to this hazard relative to earthquakes, wildfires and dam failures and the potential for losses is comparatively less.
The geographic extent of this hazard is limited to 1) Encinitas coastline, particularly “Restaurant Row” in Cardiff (south of San Elijo State Beach Campgrounds); 2) Escondido, Encinitas and Cottonwood Creeks; and 3) low-lying areas of Leucadia and Old Encinitas. The city has experienced some property-related losses resulting from localized flooding in Leucadia and coastal flooding in Cardiff, but not loss of life. Winter storms in 1997, 2005-2006 and 2010-2011 resulted in significant damage and required emergency protective measures, debris removal and reconstruction of infrastructure. The associated recovery costs (FEMA public assistance) for the 2005-06 event were over $500,000. Recovery costs for the 2010-2011 event were approximately $30,000.