Water Level Control and Tidal Flows

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Fish Kills: In 1939, hundreds of dead striped bass and smelt were found in the Lake, and more frequent flushing by opening the tide gates was suggested by a pollution control official for the state Game and Fish Commission (Oakland Tribune June, 1939).

In 1949, 104 striped bass from 12 - 15 pounds and hundreds of smelt were found dead, and the City decided to let sea water into the Lake for several days (Oakland Tribune April, 1949). Also in that year, the Oakland Park Board said that the Lake had become so polluted that the health of its waterfowl was in jeopardy.

In 1951, thousands of smelt died in May and William Penn Mott Jr. cited oxygen depletion as the cause. He said workers would drain the Lake as low as possible using the tide gates. But in July of that year, "tens of thousands" of smelt died due to lack of oxygen (Oakland Tribune May and July, 1951).

Summary: Although sewer leaks, sewage overflows and storm drain flows were also causes of poor water quality, it is clear that restricted tidal flows were a significant factor in damaging the health of the Lake Merritt. Studies in 1929 and 1953 found only a handful of San Francisco Bay's plankton and invertebrate species in the Lake (Travis, 1995). Numerous fish kills led to numerous recommendations that tidal circulation be increased. Cut off from the ocean and bay, the Lake often became stagnant as nutrients and pollutants from storm drains became trapped until the occasional few days a month in the summer when the gates were opened. In the winter, clean water from the bay was typically kept out, limiting water exchange and intensifying pollution problems.

1970 - 2002: ERA OF THE NEW FLOOD CONTROL STRUCTURE

New Tide Gates and Pumps: In response to the flood of 1962, the County of Alameda built a then state-of-the-art flood control structure complete with automated tide gates and diesel pumps that can even reverse tidal flows. Located under the bridge that now combines 7th and 8th streets, this facility was designed to prevent flooding from rainfall events up to the 25 year storm (one that, statistically, occurs once in 25 years). Larger storms, such as a 50 or 100 year storm, will still cause flooding. The station operates mainly by opening and closing tide gates to restrict flow into or out of the Lake. The facility also includes four diesel powered pumps that can move water to or from the Lake, thus providing further control over Lake level. Use of the pumps is minimal and logs show they have been used only about 1% of the time. These devices can be controlled automatically by computer, which can be set to one of four modes of Lake level control. Next >>

Photo 1: The Lake Merritt flood control station.
Photo 2: Institute Board tours the station.

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