Tuesday, May 02, 2017


by Bob Walsh

Trinity Lake is about 125 miles north-west of Lake Oroville. it is the third largest reservoir in the formerly great state of California and is, like Lake Oroville, retained by an earth-filled dam. About this time last week it was at 97% of capacity and the surrounding snow pack is about 160% of historic normal. If the reservoir were to overtop it could be very, very nasty for the down-stream residents and infrastructure, both of which are significantly fewer in number than the down-stream situation from the Oroville dam. There are only about 3,500 people in the immediate path of a dam failure there. There are almost 200,000 people down-stream from the Oroville dam.

The Trinity Lake dam is operated by the U. S. Bureau of Reclamation, while the Oroville dam is sort-of controlled by the Dept. of Water Resources, a state agency, though the actual control of the dam and reservoir is sort-of handle (or mishandled) by a southern CA. water district.

In 1996, an unusually wet year, the flow of water into Lake Trinity was about ten times that of the water going out. At that time the lake was drained down to 75% of capacity. The Trinity dam has a designed outflow of 35,000 cfs thru three outlets, one to a power plant, one thru an uncontrolled overflow tunnel and one thru a "glory hole" outlet near the base of the dam. Lake Oroville was at one time releasing 100,000 cfs over the damaged spillway.

Lake Trinity has a 3,000 square mile watershed and a capacity of 2.5 million acre-feet. Lake Oroville has a 6,000 square mile watershed and can hold 3.5 million acre-feet of water.

For some reason or other the county board of supervisors are concerned about Trinity dam. I can't imagine why.

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