Location and Description
Sepulveda Dam is a flood risk reduction project located in the south-central portion of the San Fernando Valley, just northwest of the junction of the Ventura Freeway (U.S. Highway 101) and the San Diego Freeway (Interstate Highway 405). It lies across the Los Angeles River, 43 miles above the mouth of the river, and six miles above the confluence of Tujunga Wash and the Los Angeles River.
In addition to its primary purpose of flood risk reduction, Sepulveda Dam provides recreation, agriculture and wildlife mitigation benefits. Sepulveda Dam regulates flows on the Los Angeles River and is designed to reduce the risk of flooding along the river below the dam. It forms part of the system of flood risk reduction structures located on the San Gabriel and the Los Angeles Rivers and their tributaries, which are collectively known as the Los Angeles County Drainage Area (LACDA).
Sepulveda Dam consists of an earth-filled embankment with a reinforced concrete gated spillway and gated outlet works and was completed in December 1941.
Dam Safety Issues
The primary objective of the Corps’ Dam Safety Program is to maintain public safety by making sure dams owned and operated by the Corps are safe, and the risks to the public are minimized. An integral part of the program is the risk-informed screening process. Dams are classified based upon confirmed or unconfirmed dam safety issues, the combination of life or economic consequences should failure occur and the probability of failure. This process enables us to prioritize dam safety actions to correct deficiencies, which include interim risk reduction measures to be undertaken while further investigations are conducted and remedial actions are implemented.
Sepulveda Dam received a Dam Safety Action Class III, or DSAC III, rating in March 2009 based on a Screening Portfolio Risk Analysis, or SPRA, completed in May 2008. A DSAC III rating is given to dams where the dam is significantly inadequate, or the combination of life, economic or environmental consequences with probability of failure is moderate to high.
Sepulveda Dam received a DSAC III rating because of the potential for:
· Deformation between embankment/outlet interface, resulting from the Maximum Credible Earthquake.
· Deformation of the embankment could cause loss of embankment height.
· Failure from overtopping resulting from a Maximum Probable Flood.
As a result of Sepulveda Dam’s DSAC III rating, the Corps has implemented the following Interim Risk Reduction Measures, or IRRMs:
· Inspection and monitoring. Perform physical inspections to monitor the downstream toe for potential seepage and groundwater monitoring when the pool equals elevation 700 feet, NVGD for more than one day or when groundwater data indicates that seepage is possible.
· Emergency Action Plan Update. Update the emergency action subplan annually to include the notification (contact) lists and special inspections for investigating seepage at the embankment. The package will also be updated upon completion of the updated flood mapping.
· Pre-Positioning of Materials Study. The first phase of this measure proposes that the District determine the type, volume, locations for, source of and cost of placement of stockpiled materials (gravel, fill and geotextiles) at a location near the toe of the dam to be used for emergency repair of the dam’s embankment, if necessary. Once the first phase of this IRRMP is complete, the required volume of material to be stockpiled will be obtained and placed in the predetermined stockpiled location. Implemented by 2014.
Public Safety is Number One Priority
Public safety is our number one priority. While we cannot completely eliminate risk, we can reduce it. Our screening and classification of Sepulveda Dam does not mean that failure is taking place. It means we have identified dam safety issues that don’t meet industry standards and the risk to public safety is unacceptable. Routine inspections and operation of the dam will continue and emergency action plans have been developed in coordination with local emergency management officials. Currently, there is no evidence to suggest an emergency situation exists or is about to occur.
The U.S. Army Corps of Engineers owns and operates 694 dams that serve a variety of purposes, including navigation, flood damage reduction, water supply, irrigation, hydropower, recreation, environmental enhancement and combinations of these purposes. As part of our responsibility in managing these dams, the Corps has a comprehensive Dam Safety Program that has public safety as its primary objective. Corps dams are routinely inspected and continually evaluated for safety in compliance with the Federal Guidelines for Dam Safety issued in 1979 and Engineering Regulation ER 1110-2-1156, Safety of Dams – Policy and Procedures.