Saturday, June 30, 2012

Ambitious Davidson Ditch brought water to Fairbanks dredges

Davidson Ditch inverted siphon across U.S. Creek

“Ditch” is such a mundane word and certainly doesn’t accurately describe the Davidson Ditch, the 90-mile long system of open earthwork canals, steel pipe and tunnel that carried water from the upper reaches of the Chatanika River to the Fairbanks Exploration Company's gold dredges near Fairbanks. The open canal section (83.5 miles total), with a width of 12-feet and depth of almost four-feet, was as large as some of the early tow-boat canals on the East Coast. But whoever coined the name for the system evidently liked alliteration and Davidson Ditch had more panache than Davidson Aqueduct.

Large-scale placer mining operations weren’t considered feasible in Fairbanks before the 1920s because of the huge volumes of water needed and inadequacy of local streams. For instance, Gold Dredge No. 8 used 9,000 gallons per minute, and five of the FE Co.’s dredges were supplied via the Davidson Ditch.

However, the same factors that allowed the FE Co. to move into the Fairbanks area (opening of the Alaska Railroad and development of the Healy coal fields) also allowed mining engineers to develop large-scale waterworks necessary to make dredging profitable.

James Davidson, the mining engineer responsible for the 50-mile long Miocene Ditch on the Seward Peninsula, designed the Davidson Ditch. We talk about “green” technology now, but in 1925 the proposed aqueduct was as green as you could get. The entire system was gravity fed — no pumps.

From the containment dam just below Faith and McManus Creeks (southwest of 12-mile Summit) open ditches gradually descended along ridge lines.

When the ditch reached a stream valley, inverted siphons made of 48- to 56-inch diameter pipe (15 siphons total) channeled the water down across the stream and back up the opposite slope. Thus was water brought to the Cleary Creek dredges at Chatanika. But the water was also destined for the Goldstream Valley and the final obstacle was the ridge at the head of Vault Creek just north of Fairbanks. Too high to bring a ditch across, a 3,700-foot long tunnel was blasted though the ridge’s crest.

According to John Boswell's book, "History of Alaskan Operations of United States Smelting, Refining and Mining Company," work on the ditch began in 1924 and ended by 1928. Construction required steam and diesel shovels, tractors and graders, and plenty of handwork. (The steam shovels used came from the Panana Canal project.) The FE Co. operated the ditch until 1958 when it began reducing its Fairbanks operations.

Photographs and supporting information in the Archives at the University of Alaska, Fairbanks indicate that ownership of the ditch was transferred to the Chatanika Power Company (CPC) in 1958. The CPC built a small hydroelectric plant at Chatanika and provided electricity to Fairbanks during summers from 1959 to 1967. In 1967 the same torrential rains that flooded Fairbanks also caused extensive damage to the Davidson Ditch’s containment dam and the system was abandoned.

Much of the project’s steel pipe has been removed, but portions of the ditch still exist within the Bureau of Land Management’s White Mountains National Recreation Area north of the Steese Highway. A few of the siphons are easily visible, such as the one (shown in the drawing) that crosses U.S. Creek at Mile 57.5 of the highway.

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