The main force on an embankment dam is the force of the water. The weight of the dam is also a force, but each material has a different weight, so it is not shown here as one force the way it is on the concrete dams. The uplift force is also acting on the embankment dam, but some of the water seeps into the dam so the force is not the same as on a concrete dam.
The embankment dam is the only dam type that is not made of concrete. Embankment dams may be made of earth or rock, both of which are pervious to water that is, water can get into it. You see above that the water will seep into the core material and should stop at the seepage line. The core material is usually more watertight than the rock or earth that is on the outside of the dam, but the core material is still not totally impervious to water. Concrete is not truly impervious either, but it does not allow as much seepage as these materials do.
The diagram shown to the right is only one configuration of what an embankment dam may look like. It could be any combination of earth, rock, and core material in any number of arrangements. Other forces that may act on an embankment dam are:
There may be water on the downstream side of the dam as well; this water will have the same sort of vertical and horizontal forces on the dam as the water on the upstream side
Internal hydrostatic pressure: in pores, cracks, joints, and seams
Silt pressure: silt will build up over time on the upstream side. Silt provides about one and a half times the horizontal pressure of water and twice the vertical pressure of water
Ice load on the upstream side
Wave load on the upstream side
Settlement of the foundation or abutments
Other structures on top of the dam -- gates, bridge, cars, etc.
Current CALIFORNIA Dam Failure Hazard Mitigation Efforts
Since 1929, the state has supervised all non-federal dams in California to prevent failure for the purpose of safeguarding life and protecting property. Supervision is carried out through the state’s Dam Safety Program under the jurisdiction of the Department of Water Resources. The legislation requiring state supervision was passed in response to the St. Francis Dam Failure and ongoing concerns about the potential risks to the general populace from a number of water storage dams. The law requires:
Examination and approval or repair of dams completed prior to August 14, 1929 (the effective date of the statute)
Approval of plans and specifications for and supervision of construction of new dams and the enlargement, alteration, repair, or removal of existing dams
Supervision of maintenance and operations of all dams under the state’s jurisdiction
The 1963 failure of the Baldwin Hills Dam in Southern California led the legislation to amend the California Water Code to include within state jurisdiction both new and existing off-stream storage facilities.
Dams and reservoirs subject to state supervision are defined in California Water Code Sections 6002 through 6004, with exemptions defined in Sections 6004 and 6025. In administering the Dam Safety Program, the Department of Water Resources must comply with the provisions of the California Environmental Quality Act. As such, all formal dam approval and revocation actions must be preceded by appropriate environmental documents.
In 1972, Congress moved to reduce the hazards from the 28,000 non-federal dams in the country by passing Public Law 92-367, the National Dam Inspection Act. With the passage of this law, Congress authorized the US Army Corps of Engineers to inventory dams located in the United States. The action was spurred by two disastrous earthen dam failures during the year in West Virginia and South Dakota that caused a total of 300 deaths.
The Water Resources Development Act of 1986 (Public Law 99-662) authorized the US Army Corps of Engineers to maintain and periodically publish an updated National Inventory of Dams. The Water Resources Development Act of 1996 (Public Law 104-303, Section 2215), reauthorized periodic updates by the Army Corps of Engineers. Section 215 further established the National Dam Safety Program and named the Administrator of FEMA as its coordinator. The Dam Safety Act of 2006 (Public Law 109-460) reauthorized the National Dam Safety Program through 2011.
FEMA has recently launched an effort under its Risk MAP program to communicate risk of dam failure and to coordinate state and private mitigation and preparedness efforts. According to FEMA, most people living downstream of a dam are unaware of the potential hazards associated with dam failure, have never seen the respective dam failure inundation maps, and are unaware of an evacuation plan or an Emergency Action Plan associated with the failure of that dam. There is a need, therefore, to include dam failure risk awareness as part of a comprehensive flood risk communications strategy and develop a communications strategy that reports on dam failure risk and promotes dam safety. The audience for these strategies includes dam owners/operators, dam regulators, emergency managers, floodplain managers, planners, public and private decision makers and the population at risk.
Mitigation of dam failure is constantly occurring at both the federal and state level. For example, the US Bureau of Reclamation is planning to replace the longest earthen section of Folsom Lake’s dam in order to mitigate earthquake damage. At the state level, officials are currently reviewing an $84 million project to remove a 106-foot-high dam on the Carmel River to mitigate earthquake damage and deal with flood safety issues. These are just two examples of the numerous dam mitigation projects currently being undertaken.
Engineers and engineering geologists at the California Division of Safety of Dams review and approve plans and specifications for the design of dams and oversee their construction to ensure compliance with the approved plans and specifications. Reviews include site geology, seismic setting, site investigations, construction material evaluation, dam stability, hydrology, hydraulics and structural review of appurtenant structures. In addition, division engineers inspect over 1,200 dams on a yearly schedule to ensure they are performing and being maintained in a safe manner.
There are 696 high hazard dams in the State of California. The progress report below describes a subsection of those high hazard dams that are on the remediation list.
Progress Summary 6.G: Remediation
Progress as of 2010: For the period 2007-2009, remediation needs were identified at 45 dams, of which 30 are high hazard. Remediation was completed at 77 dams, of which 51 are high hazard. The remediation included work to address remediation needs identified before 2007. As of July 2010, remediation was under way (i.e., identified or under construction) at 102 dams, of which 72 are high hazard.
Opportunities for Enhanced Dam Failure Hazard Mitigation
Cal EMA is required by state law to work with other state and federal agencies, dam owners and operators, floodplain managers, planners and public in making available dam inundation maps for the benefit of citizens interested in learning their dam failure inundation risk. Dam inundation maps can be useful in the preparation of Local Hazard Mitigation Plans and general plan safety elements updates. An opportunity for enhanced outreach to local governments and the public lies with inclusion of digital dam inundation mapping data on the MyPlan website under design by Cal EMA.
Levee and dam failures can result from a number of natural or human caused threats such as earthquakes, erosion of the face or foundation, improper sitting, rapidly rising flood waters, and structural/design flaws.
A dam failure will cause loss of life, damage to property, and other ensuing hazards, as well as the displacement of persons residing in the inundation path. Damage to electric generating facilities and transmission lines could also impact life support systems in communities outside the immediate hazard areas.
Governmental assistance could be required and may continue for an extended period. These efforts would be required to remove debris and clear roadways, demolish unsafe structures, assist in reestablishing public services and utilities, and provide continuing care and welfare for the affected population including, as required, temporary housing for displaced persons.
In Orange County, seismic activity can compromise the dam structures, resulting in catastrophic flooding. There are several earthquake faults located in close proximity to local dams and hundreds of thousands of individuals are in the inundation zones.
The dams in Orange County are also considered as potential terrorist targets. The weapon most likely to be used would be explosives with the goal of collapsing the dam. Such an event would result in a dam inundation event with little or no warning. The potential of using other types of weapons such as chemical or biological are considered low due to the large amount of material that would be required to contaminate dams used as reservoirs (drinking water).
There are a total of 32 dams in Orange County. The ownership ranges from the Federal government to Home Owners Associations. These dams hold billions of gallons of water in reservoirs. The major reservoirs are designed to protect Southern California from flood waters and to store domestic water. Their sizes range from 18 acre-feet to 196,235 acre-feet (Prado Dam) holding capacity. The following is a list of the larger reservoirs and dams in Orange County and their Owners/Operators:
Table - Largest Dams and Reservoirs Located in Orange County
Irvine Ranch Water District and Serrano Irrigation District
Villa Park Dam
Orange County Flood Control District
Irvine Ranch Water District
Olive Hills Reservoir
City of Anaheim
El Toro Reservoir
El Toro Water District
San Joaquin Reservoir
Owned by a number of water districts and operated by the Metropolitan Water District of Southern California
Sulpher Creek Dam
County of Orange
Peters Canyon Dam
County of Orange
Army Corps of Engineers, Los Angeles District
Santiago Dam is an earth fill structure with a 25,000 acre-feet capacity reservoir (Irvine Lake). The dam is jointly owned by the Irvine Ranch Water District and the Serrano Irrigation District.
Villa Park Dam
Villa Park Dam is a flood control dam located downstream from Santiago Dam. It is an earth-fill structure with a capacity of 15,600 acre-feet and is owned by the Orange County Flood Control District.
Initial alerting is expected from Dam keepers who are on duty at both Santiago Dam and Villa Park Dam
Rattlesnake Dam is an earth-filled structure with a storage capacity of about 1,700 acre-feet with a surface area of approximately 46 acres. The reservoir is owned by the Irvine Ranch Water District is presently being used for the storage of pressure pipe treated sewage effluent which in turn is used for irrigation.
Alerting is provided by Operations personnel at the Irvine Ranch Water District who will notify the Sheriff’s Department Control One of dam failure or possible dam failure.
Olive Hills Reservoir
Olive Hills Reservoir is an earth-filled asphalt lined structure owned by the City of Anaheim and is operated by the Anaheim Water Department. The Olive Hills reservoir has a storage capacity of about 197 acre-feet with a surface area of approximately 555 sq. feet. The reservoir presently is used for the storage of potable water for use by residents of the City of Anaheim.
Alerting comes from Operations personnel at the Olive Hills Reservoir who will make the initial call to Anaheim authorities who, in turn, would the contact Sheriff’s Department Control One.
El Toro Reservoir
El Toro Reservoir is an earth-filled structure owned by the El Toro Water District. The impounded reservoir has a storage capacity of about 722 acre-feet with a surface area of approximately 20.6 acres. The reservoir is presently being used as a seasonal and operational storage site for the El Toro Water District's imported Colorado River Water.
Alerting comes from Operations personnel at the El Toro Water District who will notify the Sheriff’s Department Control One of dam failure or possible dam failure.
San Joaquin Reservoir
San Joaquin Reservoir is an earth-filled structure is jointly owned by a number of water districts and is operated for these agencies by the Metropolitan Water District of Southern California. The reservoir has a storage capacity of about 3,000 acre-feet with a surface area of about 54 acres. San Joaquin Reservoir is a water supply reservoir.
Alerting comes from Operations personnel from the Metropolitan Water District who will notify the Irvine Ranch Water District who, in turn, will notify the Sheriff’s Department Control One of a dam failure or a potential dam failure.
Sulpher Creek Dam
Sulpher Creek Dam is an earth-filled structure owned by Orange County. It has a capacity of 382 acre-feet and maintained at a water surface elevation of 189 feet above MSL.
Alerting comes from the Park Ranger on duty who will notify Sheriff’s Department Control One of a dam failure or potential dam failure.
Peters Canyon Dam
Peters Canyon Dam is an earth-filled structure owned by Orange County and has a capacity of 626 acre-feet at the spillway pipe elevation of 537 feet MSL. Water stored varies from 200 acre-feet to 600 acre-feet depending on seasonal rain amounts.
Alerting would come primarily from the Park Ranger at Peters Canyon Regional Park who would notify the Sheriff Department, Control One of dam failure or possible dam failure.
Prado Dam is owned and operated by the Los Angeles District, Corps of Engineers and was constructed for the primary purpose of providing protection from floods for the metropolitan areas in Orange County, California. Installation of the Seven Oaks Dam in San Bernardino County has lessened the impact of a Prado Dam failure.
In the event that downstream interests need to be alerted, the Corps of Engineers will contact the following:
Orange County Sheriff’s Department Control One
Riverside County Disaster Preparedness
California Emergency Management Agency, Sacramento
Once contacted, the above agencies will notify all pertinent Federal, state, county and local agencies through the state's National Warning System hookup (fan out communication system).
Table - Large Orange County Reservoirs
Name of Facility Owner
Santiago Reservoir (Irvine Lake) Orange County
Villa Park Dam Orange County
Sulpher Creek Dam Orange County
Peters Canyon Dam Orange County
Walnut Canyon Reservoir City of Anaheim
San Joaquin Reservoir Irvine Ranch Water District
Sand Canyon Reservoir Irvine Ranch Water District
Rattlesnake Canyon Reservoir Irvine Ranch Water District
Big Canyon Reservoir City of Newport
Lake Mission Viejo Lake Mission Viejo Association
El Toro Reservoir El Toro Water District
Orange County Reservoir Metropolitan Water District
Palisades Reservoir South Coast Water District
Portola Reservoir Santa Margarita Water District
Syphon Canyon Reservoir The Irvine Company
Trabuco Dam Trabuco Canyon Water District
Upper Oso Dam Santa Margarita Water District
Brea Dam U. S. Army Corps of Engineers
Fullerton Dam U. S. Army Corps of Engineers
Carbon Canyon Dam U. S. Army Corps of Engineers
Dam Failure Flooding
Loss of life and damage to structures, roads, and utilities may result from a dam failure. Economic losses can also result from a lowered tax base and lack of utility profits. These effects would certainly accompany the failure of one of the major dams in Orange County. There are 10 major dams or reservoirs in Orange County some of which hold millions of gallons of water. Because dam failure can have severe consequences, FEMA and the California Emergency Management Agency require all dam owners develop Emergency Action Plans for warning, evacuation, and post-flood actions. Although there may be coordination with county officials in the development of the Emergency Action Plans, the responsibility for developing potential flood inundation maps and facilitation of emergency response is the responsibility of the dam owner.
For more detailed information regarding dam failure flooding, and potential flood inundation zones for a particular dam in the county, refer to the Orange County, Operational Area Emergency Action Plan as well as the Cities of Costa Mesa, Fountain Valley, Garden Grove, Huntington Beach, Newport Beach, Seal Beach and Westminster Emergency Operations Plans.
Historical Failure Flooding
Westminster Water Tank Failure
In September of 1998, a smaller version of a municipal water storage unit in the City of Westminster failed, collapsing about 12 feet of the 100,000 gallon tank. The flow of water from the tank destroyed most of the facility as well as several private residents. Luckily, the home that was hit hardest was not occupied at the time. Additionally, there were approximately 30 more homes inundated with water and silt. An Orange County Fire Authority fire station was located within 100 feet of the water tank. Firefighters were swept through the fire station by the large quantity of water. Through the Public Works Mutual Aid Agreement, the Orange County Public Works Department assisted in the clean up and temporary repair of the streets.
St. Francis Dam
The failure of the St. Francis Dam, and the resulting loss of over 500 lives in the path of a roaring wall of water, was a scandal that resulted in the almost complete destruction of the reputation of its builder, William Mulholland. It was he who proposed, designed, and supervised the construction of the Los Angeles Aqueduct, which brought water from the Owens Valley to the city. The St. Francis Dam, built in 1926, was 180 feet high and 600 feet long; it was located near Saugus in the San Francisquito Canyon. Because Los Angeles County is adjacent to Orange County, the tales of this incident have been passed down by several generations.
The dam gave way on March 12, 1928, three minutes before midnight. Its waters swept through the Santa Clara Valley toward the Pacific Ocean, about 54 miles away. Sixty-five miles of valley was devastated before the water finally made its way into the ocean between Oxnard and Ventura. At its peak, the wall of water was said to be 78 feet high; by the time it hit Santa Paula, 42 miles south of the dam, the water was estimated to be 25 feet deep. Almost everything in its path was destroyed: livestock, structures, railways, bridges, and orchards. By the time it was over, parts of Ventura County lay under 70 feet of mud and debris. Over 500 people were killed and damage estimates topped $20 million.
Baldwin Hills Dam
The Baldwin Hills dam failed during the daylight hours, and was one of the first disaster events documented by a live helicopter broadcast. The telecast of the collapse from a KTLA-TV helicopter is considered the precursor to airborne news coverage that is now routine everywhere.
The Baldwin Hills Dam collapsed with the fury of a thousand cloudbursts, sending a 50-foot wall of water down Cloverdale Avenue and slamming into homes and cars on December 14, 1963. Five people were killed. Sixty-five hillside houses were ripped apart, and 210 homes and apartments were damaged. The flood swept northward in a V-shaped path roughly bounded by La Brea Avenue and Jefferson and La Cienega Boulevards.
The earthen dam that created a 19-acre reservoir to supply drinking water for West Los Angeles residents ruptured at 3:38 PM. As a pencil-thin crack widened to a 75-foot gash, 292 million gallons surged out. It took 77 minutes for the lake to empty. But it took a generation for the neighborhood below to recover. Two decades passed before the Baldwin Hills ridge top was reborn. The cascade caused an unexpected ripple effect that is still being felt in Los Angeles and beyond. It foreshadowed the end of urban-area earthen dams as a major element of the water storage systems. It prompted a tightening of Division of Safety of Dams control over reservoirs throughout the state.
Coast Community College District Threat of Dam Failure
The Seven Oaks and Prado Dams are the dams that threaten CCCD facilities. The Seven Oaks Dam is located above Prado dam and feeds in to Prado Dam; Prado Dam feeds into the Santa Ana River; the Santa Ana River flows through or is adjacent to 13 of the CCCD 15 sites.
CCCD Dam Failure Issues
The CCCD facilities in the cities Costa Mesa, Fountain Valley, Garden Grove, Huntington Beach, Irvine, Newport Beach, Seal Beach and Westminster are subject to potential flooding from two dams, Prado and Seven Oaks. These two dams are located to the northeast of Orange County in San Bernardino County. The Seven Oaks Dam feeds into Prado Dam. They are considered the only two dams that could fail and potentially impact the coastal Orange County area. The impact could cause loss of life, destroy thousands of high dollar properties and damage residential, business and educational facilities as well as hurting tourism in the area. The economic losses could be great.