OAKLAND -- It was in the early 1960s when extreme flooding of Lake Merritt severely damaged nearby businesses and made travel on adjacent streets and sidewalks a dangerous venture. At one point in 1962, an abnormally high tide coupled with a record 4.47 inches of rain in 24 hours caused the lake to rise to 7.3 feet, 4 feet higher than normal -- the highest level ever documented.
But those days are a thing of the past. A state-of-the-art partly submerged pumping station at the 7th Street Bridge keeps the fluctuating lake water levels in check and has successfully done so for more than 40 years.
"It was (because) of the storms of the 1960s that the board of supervisors said 'we have to do something'," said Gene J. Mazza, pump station supervisor with the Alameda County Flood Control & Water Conservation District.
Consulting engineers Brown and Caldwell were hired to study, design and develop a proposed facility, Mazza said.
Construction was approved in 1968 and completed in 1971, Mazza said.
The approved $1.8 million project addressed flooding plus the extensive recreational use of Lake Merritt and realigning the outfall channel passing through Laney College campus to include a scenic lake.
Along with providing a safeguard against the flooding of the lake and the surrounding 4,670 acres of residential and commercial property, the pumping station was constructed to aid in the improvement of water quality.
"Even though our primary mission is flood control," Mazza said, "we also realize there is the other part of it ... keeping the lake smelling good and keeping the fish life, marine life abundant."
The four 63-inch-diameter horizontal turbine pumps were all rehabilitated in the 1980s and upgrades were made to the upstream (lake side) and downstream (bay side) gate structures.
The station proved its worth in the 1981 deluge and again two weeks ago whenï»¿ a 7-foot king tide inundated the shoreline. ('King tide' is a nonscientific term used when referring to the very highest tides and is a naturally occurring predictable event.)
"That 7-foot tide would have pretty much filled the lake," Mazza said.
If that tide had been accompanied by torrential rains or what is called a hundred-years storm the pumps would run nonstop, pumping 4,400 gallons a minute, Mazza said.
But running all four pumps 24/7 is not routine nor is it desired because of the cost and efficiency. Instead, the lake waters are kept at a prime level by opening and closing the tide gates. Only when the tide is in must the pumps, driven by 231-horsepower diesel engines, be used.
"We prefer to gravity flow," Mazza said. "We can gravity flow twice as much as we can pump. It's harder to pump against a column of water like on a high tide. It's easier to gravity flow it out, it's more free flowing. We have two sides of gravity flow; on the pumps we only have one side."
A combination of both gravity flow and pumping is used when it rains.
Mazza pays attention to the National Oceanic and Atmospheric Administration's weather website two or three times a day during the rainy season.
An engineer regularly checks the controls and, before leaving for the night, sets the station to automatic.
"We put it in automatic operations so the station will know that if the water in the lakes starts to rise (and) if the tide is out, the gates will open and gravity out," Mazza said.
In essence, it tells itself, "'I'm going to start my pumps,'" he said. "It's all automatic."
The lake can also be remotely monitored through SCADA (supervisory control and data acquisition), a computer-controlled system, that was installed in 2004. The ability to remotely change settings is expected to happen in the future.
7th Street Pumping Station
The 7th Street Pumping Station is also known as the Lake Merritt Storm Water Lift Station. It took three years to build and cost about $1.8 million.
SOURCE: Alameda County Flood Control & Water conservation District
about lake merritt
Lake Merritt began as a broad tidal estuary where fresh water mixed with the bay's salt water known as Laguna Peralta. Its shoreline extended north to where the Grand Lake Theater now stands and a wide, shallow slough surrounded by tidal marsh and mud flats connected it to the San Antonio Creek (Oakland Estuary). It had abundant wildlife and native vegetation.
In 1869, Mayor Samuel Merritt gave money to build a dam at the 12th Street bridge thus creating "Merritt's Lake." Reclamation of the wetlands confined the slough to a narrow corridor limiting the exchange of tidal waters in the new lake. In 1870, the U.S. Congress declared Lake Merritt a national wildlife refuge, the first in North America.
Source: Oakland Public Works