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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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May 13

Happy 100th Birthday, Alpine Dam!

Posted on May 13, 2019 at 9:06 AM by Ann Vallee

Alpine Dam under construction in 1918

 Alpine Lake Jan 2017
Nestled deep in MMWD’s beautiful Mt. Tamalpais Watershed, Alpine Dam continues to play an integral role in supplying clean, local water to our customers—a full century after its construction.

Even at 100 years old, Alpine is not the oldest dam in our system. Both Lagunitas (1872) and Phoenix (1905) were built before MMWD was established. After MMWD’s creation in 1912, one of the water district’s first actions was issuing a $3 million bond to build Alpine Dam to serve Marin’s growing population. Today, replacing the dam would cost an estimated $200-$300 million.

Work on Alpine began in the summer of 1917, but the outbreak of WWI caused difficulties for the contractor as labor and supplies became difficult to secure. MMWD took over construction in January 1918, completing work in January 1919. Alpine was dedicated in a dam-top ceremony on June 21, 1919.

Alpine is unique among MMWD’s seven dams as the only concrete one in our system (all the others are earthen). When it was built, the dam contained 27,719 cubic yards of concrete and held just over a billion gallons of water. The dam was raised in 1924 and again in 1941 to its current capacity of nearly 2.9 billion gallons—about 11% of our total water storage capacity.

Originally, water from Alpine traveled via gravity through Pine Mountain Tunnel and miles of concrete pipeline, then on to customers’ homes and businesses. Today, water from the lake is pumped up to Bon Tempe Reservoir for treatment at Bon Tempe Treatment Plant before supplying the southern part of our service area. When Alpine is full, water flows over its dramatic spillway and into Kent Lake. From there the water can travel on to San Geronimo Treatment Plant, or it can be released to support fish and other wildlife downstream in Lagunitas Creek. Alpine thus remains at the heart of our water supply system. Along with maintaining our pipes and storage tanks, taking care of Alpine and our other reservoirs is critical to ensuring a reliable water supply for the next 100 years and beyond.


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