One of the most ambitious engineering projects in Marin County, commissioned by the fledgling MMWD, was the design and construction of Alpine Dam and its complex water delivery system built 100 years ago. While building a dam is a remarkable achievement, digging a mile and a half long tunnel through solid rock is astounding.
The location of Alpine Dam -built at the confluence of Cataract and Lagunitas Creeks- was not well situated to easily convey water to the growing towns surrounding San Rafael. The natural route of the water flowing down the northern side of Mt. Tam was via Lagunitas and Papermill Creeks and then out to Tomales Bay. In 1918, water pumps were crude, bulky and low capacity so it made economic sense to build dams where gravity would carry the water to its ultimate destination.
An ambitious plan was formulated to use gravity to convey water to Marin’s population centers by drilling a tunnel through Pine Mountain which was blocking the way.
The project began with the construction of a new road to carry a concrete pipe four miles long extending from Alpine Dam to the opening of the new tunnel. On the east side of Pine Mountain, the pipe exited the tunnel and traversed several more miles along the steep slopes above Cascade Canyon in Fairfax. It then crossed under the Bolinas-Fairfax Rd, and went beneath Five Corners and along Shaver Grade to finally connect to the 1873 Lake Lagunitas water flume at the bottom of Fish Gulch.
In his book, Mt Tamalpais and the Marin Municipal Water District, author Jack Gibson says the Pine Mountain Tunnel cost 25 percent more than the original Alpine Dam, illustrating the complexities of such a project. Alpine Dam was completed in 1919, and then raised twice –once in 1924 & again in 1942- to nearly double Alpine Lake’s storage capacity.
Jim Vitek, a life-long water district employee, used to volunteer to inspect the pipes inside the Pine Mountain Tunnel. Once a second pipe was added, he could barely fit inside, yet he managed to crawl and squeeze along the tunnel for 8,700 feet, or the length of 29 football fields. His service in the Navy during World War II probably prepared him well for that annual adventure.
Though the pipes inside are now used for water storage, MMWD plans to decommission the Pine Mountain Tunnel. The hundred-year-old tunnel is starting to deteriorate, and modern pumps now bring water from Alpine Lake directly into the system and bypass the historic tunnel entirely.