Big Gap Flume

An incredible engineering feat for 1859, the wooden Big Gap suspension flume towered 25 stories high and spanned almost one half mile across Conrad Gulch to bring water to the mines, rangeland, and farms of Groveland’s surrounding communities.

The Golden Rock Water Company hired mostly Chinese laborers to build flumes and dig associated water ditches with picks and shovels. By the summer of 1868, the Chinese laborers had dug a network of ditches for the company, totaling over 100 miles for the company. Typically, engineers instructed laborers to dig ditches and build flumes paralleling contours on the side of slopes to allow gravity to transport water over great distances. However, transporting water across the deep and wide Conrad Gulch proved to be challenging. The Golden Rock Company ultimately decided to build a wooden suspension flume across the gulch. G.W. Holt designed the suspension flume to be supported by eleven regularly-spaced towers, which were stabilized by guy wires. Built mainly from sugar pine, Holt predicted the flume would last 7 to 8 years.

Current-day engineers can only speculate on how laborers built the suspension flume without modern-day equipment. One engineer thought, “The whole 2,200 feet [suspension flume] must have been constructed 200 feet at a time and shoved ahead on rollers from one tower to the next…Just how they supported the cantilever section formed by the flume is not clear…”

Water first began flowing through the suspension flume on March 29, 1860. Many Chinese bought the water either for placer mining or for domestic purposes for the small Chinese community in northern Big Oak Flat. However, water delivery was sometimes interrupted for several months due to dirt slides into the water ditch or damage to the suspension flume.

Over time, the wooden suspension flume began to rot and decay, but the company failed to maintain the wooden towers. As a result, the legs of many of the towers began rotting and breaking away. One tower had only 1 of the 4 legs remaining, and was entirely supported the guy wires. Finally in the early morning of July 9, 1868, during a summer wind storm, the Big Gap Flume collapsed. It fell “with a tremendous crash…leaving scarcely a beam erect – vast heap of broken and rotten timbers.”

Less than a year after the collapse of the Big Gap Flume, the Golden Rock Water Company successfully secured materials for an iron pipe to replace the flume. With the cooperative help of 2000 miners, which undoubtedly included Chinese, the miners installed the siphon pipe along the surface of the gulch in a short 2 months. Water began flowing through the pipe on July 30, 1869, and served the community for several more decades. It is unclear when the pipe was last used, but the water ditches were last used in 1923 to supply water for fire protection in Groveland and for railroad and associated buildings in the local area. The ditches lost their importance after Hetch Hetchy was built, and Tuolumne County acquired it in 1942 after the ditch owner failed to pay property taxes.

No known wood exists from the Big Gap Flume, as the wood is susceptible to rot and fires that have passed through the area since 1868. The only remnants left of the Big Gap Flume are dirt mounds where anchors were buried. Cables from the towers were attached to the anchors to prevent lateral tower sway.

The iron bolted pipe measuring 22” in diameter still spans across the surface of the gulch on either side of Highway 120. Depending on your vantage point and the extent of vegetation growth, the pipe is still visible as of 2016. The pipe pathway marks the same pathway where the Big Gap Flume once stood. Deep ditches dug by the Chinese laborers still exist near the top of each of the 2 ridges where the pipe ends.

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