Uncommonly Heavy May Rain Results In Five Times Normal Dam H2O Release

Significantly heavier rainfall than has historically been the case in May has resulted in the Orange County Flood Control District releasing a substantially greater amount of water from the Seven Oaks Dam than is normally the case at this time of year.
At times the water release through the 1,623-foot long tunnel outlet running through the base of the structure reached 700 cubic feet per second, more than five and a half times the normal flow of  125 cubic feet per second done during normally scheduled six-day release periods.
Seven Oaks Dam is a 2,980-foot-long arched embankment structure that at its apex is 550 feet above the Santa Ana River and 650 feet above its deepest foundations. Forty feet wide at its crest and more than 2,200 feet wide at its base, Seven Oaks has a gross storage capacity of 145,600 acre feet, with 113,600 acre feet reserved for flood control and the remainder for sediment accumulation. At full pool, the reservoir lies at an elevation of 2,604.4 feet and has an area of 780 acres. Water releases are controlled by the aforementioned 1,623-foot length tunnel base outlet as well as a 500-foot  wide ungated overflow spillway located southeast of the dam.
Situated proximate to the San Andreas Fault, the dam is designed to withstand an 8.0 Richter Scale earthquake.
Standing at the headwaters of the Santa Ana River, the dam collects runoff from a 176 square mile area or 209 square miles when the drainage area of Baldwin Lake is included. During deluges, Baldwin Lake’s overflow is vectored into the Santa Ana River system.
Given that the Santa Ana River wends its way through San Bernardino, Riverside and then Orange County before reaching the Pacific Ocean, and the area along its banks in Orange County serves as a major water source in Orange County, Orange County has historically taken an interest in preserving and securing its downriver flow. Generations ago, Orange County acted to tie up much of the property
around the headwaters.
After more than a decade of planning and preparation involving the U.S. Army Corps of Engineers, the State of California, and the counties of San Bernardino, Riverside and Orange, a contract for Seven Oaks Dam was awarded in 1994, with the federal government picking up 70.47 percent of the cost, Orange County defraying 27.09 percent of the price of the undertaking, San Bernardino County chipping in 1.71 percent, and Riverside County laying out 0.73 percent. Cost overruns on the project raised its final price tag to $450 million.
Construction work began in May 1994 and continued until just before its dedication in January 2000.  To create the dam’s embankment, earth was excavated from the Santa Ana River canyon immediately below the dam, the alluvial fan of the river north of Mentone, and a cut in a ridge just southeast of the dam that now serves as the dam’s spillway.
Care must be taken in releasing water from the dam, as inundating the Santa Ana with too much flow can prove devastating to the riparian habitat for many creatures that live in the river, such as the endangered Santa Ana Sucker, as well as ones that nest or dwell along its banks.
High water levels can be dangerous to humans, as well. Trails that run along the river were closed during the water releases, which typically go for several days at a time. Additionally,  before the water release as well as during it the sheriff’s department sent personnel to survey the run of the river at ground level and detailed its helicopters to fly above the river to locate, warn and remove elements of the county’s homeless population who have camped down along the river’s banks
-Mark Gutglueck

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