Water Level Control and Tidal Flows

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Natural Flushing Still Restricted: Despite the enhanced ability to control Lake level and a century of evidence that reduced tidal flows exacerbate water quality problems, a 1975 report noted an "absence of natural flushing" (Travis, 1995). Data from the Alameda County Flood Control District showed that between 1972 and 1973 exchange with the Oakland Inner Harbor occurred on an average of only 8 days per month. Often the gates would remain closed for several days to a week or more at a time (CA RWQCB, 1975). Articles in the press indicated that only during times of a crisis such as a fish kill would the gates be open on a daily basis (Oakland Tribune July, 1974 and May, 1976).

Improvements: The 1975 study suggested flushing as the most practical water quality management program, and by the late 70's the Lake was receiving more regular tidal inflow. A 1979 study commissioned by the City listed flushing of the Lake using the pump station as a high priority recommendation (Pitt and Bozeman, 1979) and tests were conducted (ACFC&WCD and CH2M-Hill, 1982). During these experiments larger than normal volumes of water were pumped into the Lake. It was determined however that dredging the entire Lake was a better long term solution to the Lake's problems, and artificial flushing was not adopted.

In the 1980's the County allowed more frequent natural tidal flows but maintained a flood control policy which kept the gates closed during high tides for any ten day period during which rain was forecast. The result was that the Lake level was kept low (around 1 foot above mean sea level) and inflow from high tides was kept out for much of the winter (Travis, 1995). Combined with improvements in water quality from sewer repairs, this policy has led to the elimination of fish kills, the last of which occurred in 1981 (Gray, 1990).
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