Dams, Potential Flooding & Buying a House in Earthquake Country

one-story house in California near a fault line

So far in this series, we’ve covered proximity to fault lines in part one and soil liquefaction and landslides in part two. Another area to look into before buying a house in earthquake country is proximity to dams. Their watersheds cover vast areas, causing massive flooding downstream if the dam fails during an earthquake.

Part 3: An Area of Potential Flooding

Even if the closest dam to your house is 100 miles away or more, it may still pose a danger after an earthquake. See the map below of the dams in California’s jurisdiction (federal dams not shown).

Buying a house in earthquake country - map of the dams in California
Photo Courtesy California Department of Water Resources

In February 2017, the Oroville Dam was near-breach. Additional stresses from strong rains and melting snow caused a failure. Thankfully, the dam did not completely fail. If it had, a 30-foot wave would have impacted nearby areas. RMSconnection provides a worst-case scenario animation.

The Oroville Dam crisis drew attention to California’s dams. The Division of Safety of Dams (DSOD) released a dam assessment report for California (not including federal dams) in September 2017. The graph below summarizes the report. The left-most bar shows all dams in California, grouped by their condition.  A condition of “fair” means that the dam may fail during an earthquake. A condition of “poor” or “unsatisfactory” means that safety is a concern for that dam, and retrofitting is required. The middle bar shows the dams grouped by their potential impact of failure. An impact “high” or “extremely high” means that loss of life is possible.

The right-most bar shows the subset of dams that could cause post-earthquake impact.  There are 60 dams in California that could result in loss of life if that dam fails in an earthquake.

Buying a house in earthquake country - Dam safety summary
Data taken from the DSOD report

Dams that Could Impact Human Life

Here is a list of all California dams that could result in “dam safety deficiency” after an earthquake (as of September 2017).

CountyName of Dam
Owner of Dam
City and County of San Francisco
HendersonAmador Regional Sanitation Authority
California Department of Water Resources
Contra CostaLafayetteEast Bay Municipal Utility District
Contra CostaOrinda, LakeOrinda Country Club
El DoradoEl Dorado ForebayEl Dorado Irrigation District
ImperialEl Centro Water Purification PlantCity of El Centro
InyoHaiweeCity of Los Angeles Department of Water And Power
InyoTinemahaCity of Los Angeles Department of Water And Power
Los AngelesBouquet CanyonCity of Los Angeles Department of Water And Power
Los AngelesCastaicCalifornia Department of Water Resources
Los AngelesSawpit Debris BasinLos Angeles County Department Of Public Works
MaderaCrane Valley StoragePacific Gas and Electric Company
MendocinoFeliz North LakeBrutocao Vineyards
ModocKelley Hot Spring FishPrivate Entity
MonoAgnew LakeSouthern California Edison
MonoGem LakeSouthern California Edison
MonoLower Twin LakeCentennial Livestock
MonoRush Creek MeadowsSouthern California Edison
MonoUpper Twin LakeCentennial Livestock
NapaAraujo Reservoir No. 1Kerwin Estate, LLC
NapaAraujo Reservoir No. 2Kerwin Estate, LLC
NapaConn CreekCity of Napa
NapaLake CurryCity of Vallejo
NapaSt. Helena LowerCity of Saint Helena
NapaVeterans HomeCalifornia Department of Veteran Affairs
NevadaLake AngelaDonner Summit Public Utility District
NevadaLake FordycePacific Gas and Electric Company
NevadaLake Van NordenTruckee Donner Land Trust
PlacerLakewoodThe Armtrout Family Trust
RiversidePerrisCalifornia Department of Water Resources
RiversideVailRancho California Water District
SacramentoBlodgettPrivate Entity
County of Sacramento
SacramentoWillow Hill ReservoirCity of Folsom
San BernardinoGlen MartinHighest and Best Use, LLC
San BernardinoGregory, LakeSan Bernardino County Regional Parks
San DiegoBarrettCity of San Diego
San DiegoEl CapitanCity of San Diego
San DiegoHodges, LakeCity of San Diego
San DiegoMorenaCity of San Diego
San DiegoMt WoodsonRamona Municipal Water District
San DiegoMurrayCity of San Diego
San DiegoSavageCity of San Diego
San DiegoSweetwater MainSweetwater Authority
San DiegoWohlford, LakeCity of Escondido
San MateoBear GulchCalifornia Water Service Company
Santa ClaraAlmadenSanta Clara Valley Water District
Santa ClaraCaleroSanta Clara Valley Water District
Santa ClaraGuadalupeSanta Clara Valley Water District
Santa ClaraLeroy AndersonSanta Clara Valley Water District
Santa ClaraNorth ForkPacheco Pass Water District
Santa CruzNewellCity of Santa Cruz
ShastaMisselbeckIgo-Ono Community Services District
SolanoLynch CanyonSolano Land Trust
SonomaLa Crema WineryJackson Family Wines
StanislausConAgra Aerated and Settling PondsConAgra Grocery Products Company, LLC
VenturaMatilijaVentura County Watershed Protection District
VenturaSanta Felicia
United Water Conservation District
YubaCamp Far WestSouth Sutter Water District

A close call occurred in 1971 after the San Fernando earthquake. As a result of the quake, the Van Norman Dam, an earth dam north of the San Fernando Valley, liquefied the top 30 feet of the dam crest. With fears of a potential failure, officials evacuated 80,000 people in the largest Los Angeles evacuation order. Thankfully, the water level of the dam was lower than usual. Therefor the water did not overtop the dam and there were no casualties. This led to increased understanding of dams made of soils.

Buying a house in earthquake country - Dam failure of 1971
Posted by USGS; Photo by J.I.Ziony, Los Angeles County, California

Prepare, Prepare, Prepare

Senate Bill 92, passed in 2017, requires the Department of Water Resources to make publicly-available inundation maps for each of its dams and provide updates every ten years. Refer to the California Department of Water Resources website for the approved inundation maps. The owners of the dams must have the maps available by January 1, 2019. For any maps not yet released, contact PRA@caloes.ca.gov to request dam inundation data.

Above all, if you are in a post-earthquake potential flooding area, it’s even more critical to have an emergency kit that includes a radio to receive evacuation alerts. Also be sure to have a communication plan with your family and a planned evacuation area.

Be mindful of your location and always be prepared.

This article is educational and informational in nature, and not intended as legal, expert or other professional advice, or as any form of recommended minimum standard or best practice. Be advised to carefully review the information presented with qualified professional advisors prior to acting upon or implementing said ideas.

Author: Camille Bhalerao

Camille Bhalerao is a writer and illustrator for Jumpstart Recovery, covering the science of earthquakes. As a Professional Engineer, she has designed marine structures (seawalls, wharves, piers, and bridges) for earthquakes. She is a member of the Structural Engineers Association of Northern California (SEAONC), where she is the marketing director for a new podcast that shares information about structural and earthquake engineering. Her passion for earthquake preparedness manifests in storing water bottles around the house, fangirling USGS, buying earthquake insurance, and sharing information with people at parties (earthquake safety moment: tables are the new door frames!).