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Aerial view of Hansen Dam

Aerial view of Hansen Dam (Photo by courtesy photo)

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Hansen Dam

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Location and Description

Hansen Dam is a flood risk reduction project located near the northern edge of the San Fernando Valley on Tujunga Wash, about one mile below the confluence of the Big Tujunga and Little Tujunga Washes, and about four miles southeast of the town of San Fernando.

The boundary of the drainage area is formed by the San Gabriel Mountains on the north and west, and by the Verdugo Mountains and a secondary range of the San Gabriel Mountains on the south and east. In conjunction with Sepulveda and Lopez dams, Hansen Dam is an essential element for flood risk reduction in the Los Angeles River drainage basin.

Hansen Dam was completed in September 1940 and is vital for the flood risk reduction of lower portions of the San Fernando Valley and the City of Los Angeles.

Hansen Dam Basin Master Plan 2011

Hasen App & EA

Final Hansen Dam Maps

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.

Current Status

Hansen 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.

Hansen Dam received a DSAC III rating because of the potential for:

  • Deformation between embankment/outlet interface, resulting from the Maximum Credible Earthquake.
  • Deformation of embankment could cause loss of embankment height.
  • Failure from overtopping resulting from a Probable Maximum Flood.

As a result of Hansen Dam’s DSAC III rating, the Corps has implemented the following Interim Risk Reduction Measures, or IRRMs:

  • A Special Dam Inspection Team will conduct an inspection when trigger elevation or the historic maximum high pool elevation of 1040 feet, NGVD has been reached.
  • Update the Emergency Action and Notification Sub-plan (known as the EAP) annually.

What’s next?

·        Flood Mapping. Given the significant local inflow to the downstream channel, a number of scenarios less severe than dam failure can cause widespread flooding in the urban area below the dam. These include controlled releases in excess of available channel capacity and various levels of spillway flow. Improved mapping of the areas most vulnerable to inundation will help decision makers during extreme events compare the consequences of making releases exceeding channel capacity versus running the risk of later spillway flows. This measure will be implemented by 2016 depending on the availability of funding.

·        Coordination with Local Interests / Table top exercise. Los Angeles District representatives will meet with city, county and state officials to outline dam safety issues and the associated failure modes. This coordination will include a flood emergency exercise to be scheduled with the potentially affected emergency management agencies. This measure will be implemented by 2015 depending on the availability funding.

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 Hansen 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.

Background

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.


dam safety DSAC Hansen Dam