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Corps of Engineers tests Sepulveda Dam crest gates Monday

USACE
Published July 24, 2015
This is a view of the Sepulveda Dam from inside the basin where water collects during rain storms. The left side of the dam shows the spillways where the gates will be tested and the right side shows the outlet passages into the Los Angeles River.

This is a view of the Sepulveda Dam from inside the basin where water collects during rain storms. The left side of the dam shows the spillways where the gates will be tested and the right side shows the outlet passages into the Los Angeles River.

With the National Weather Service forecasting an above average precipitation for this winter and the spring of 2016, the U.S. Army Corps of Engineers is staying at the ready to prevent flooding of the Los Angeles basin.

The Los Angeles District of the U.S. Army Corps of Engineers is responsible for Sepulveda Dam, one of six dams which provide flood risk management for the Los Angeles County Drainage Area.

On Monday, July 27 between 8 a.m. and 3 p.m., USACE will perform operational testing on the Sepulveda Dam spillway crest gates. The crest gates block off the spillway to provide additional, temporary storage during an extreme storm event.

“USACE policy requires routine inspection, monitoring and testing of project components to assure proper operation,” said Brian Dela-Barre, dam safety program manager. “USACE will be using a total of about 1.5 acre-feet of municipal water during the test.”

This is the first test of spillway gates in the last three years.

“The Sepulveda spillway gates are an innovative engineering design,” said District Deputy Engineer David Van Dorpe. “During the test, gate chambers will be filled with water that will cause a float to rise and the gates to move upwards.  Eventually, the floats will also fill with water and the gates will lower.  The gate chambers will then be emptied back into the Los Angeles River.  The entire system is designed to operate automatically during a major storm event.”

The gates are normally in the down position, which leaves the spillway crest at an elevation of 700 feet. When the water surface in the reservoir reaches an elevation of 692.5 feet, the spillway gates begin to rise, eventually reaching an elevation of 710 feet. The gates reach this height when the water surface in the reservoir reaches an elevation of 699 feet. If the water level in the reservoir reaches an elevation of 712 feet they will begin to lower, thus increasing the discharge capacity of the spillway.

“This water used for testing will be discharged to the channel at the river outlet works during the test and combine with the effluent discharge from the Tillman Water Treatment Plant already in the channel,” said Dela-Barre.

The change in water surface elevation within the channel will be barely discernible.  

Facilities located within the reservoir basin, such as roads, parks and golf courses, have been allowed into the basin based upon their ability to withstand occasional inundation caused when water is temporarily stored in the reservoir.

The purpose of the dam is to collect flood runoff from the uncontrolled drainage areas upstream, reducing the flood risk for 1.1 million people and $138 billion worth of property.

In addition to the spillway and its gates, the dam has eight outlet passages, which can be seen in the center of the LA River.

The “standby” position of the gated passages is wide open. During the initial stages of a flood event, Sepulveda Dam will release as much of the inflow as is physically possible. This minimizes the amount of stored water and the impact to facilities located within the basin. However, as the LA River channel downstream approaches its capacity, the Corps of Engineers begins to close the gates in the gated outlet passages.

The highest water surface elevation ever reached at Sepulveda Dam was 705.10 feet and the dam has never been forced to use its spillways! Water has always been released into the Los Angeles River through the outlet works at a rate that did not exceed the capacity of the downstream channel.

Comments or questions regarding this testing may be sent to https://spl.usace.afpims.mil/Contact.aspx