Digital Bob Archive

Mining tunnels are a prominent part of the landscape of the City and Borough of Juneau, and a few of them are still in use for one purpose or another. An Alaska Juneau Mining Company haulage tunnel in Mount Roberts, above and behind downtown Juneau, is used for water storage. For many years the Sheep Creek Adit carried the electric transmission line from the Annex Creek power house, but the tunnel had so many cave-ins that it was abandoned for that purpose. The old Jualpa drainage tunnel from Last Chance Basin is a conduit for a main pipeline of the city's water system.

Even older than the Jualpa tunnel is the Silver Bow Basin drainage tunnel, and to a non-engineer it would seem to have a potential for water storage at rather moderate cost. This tunnel was commenced in mid-July, 1889, and on January 4, 1891, reached a shaft that had been sunk in Silver Bow Basin. The length is 2,900 feet through solid rock and the drilling, estimated to have totaled 11 miles, is believed to have been done by hand. The tunnel was described, upon completion, as \"straight as a line and with an even grade of four inches to twelve feet.\"

The lower end of the tunnel, the end nearest Juneau, is 10 feet wide and 9 feet high. A section at the other end is several feet wider, to accommodate a double sluice box. It was estimated that 10,400 cubic yards of rock, equal to 22,500 tons, was removed. The tunnel tapped Silver Bow Basin at a depth of 91 feet below what was then the surface of its gravels. That surface was lowered by subsequent hydraulic placer mining.

The tunnel had a triple purpose. Ore from the Ground Hog lode claim was carried by aerial tram to the shaft, then dropped to the tunnel and hauled in cars to the Red Mill at the Juneau end of the tunnel. It also held a combination of sluice boxes and flume to drain the basin so that mining could be carried on, and to wash the gravels for gold recovery. The flume, 4 feet wide and 3 feet high, was double at the basin end and that part was fitted with riffle blocks. One half could be \"cleaned up\" to recover the gold while gravel still moved through the other.

The placer operation continued for some 11 years and the gold recovery was estimated at between $350,000 and $400,000. I have seen no estimate of the volume of gravel that was involved, but a very considerable part of the Gold Creek delta, upon which a part of Juneau is built, must have come through that tunnel.

As mentioned above, it would seem that a relatively simple engineering study could determine whether it is feasible, with a plug and a valve, to create a water storage facility not only in the tunnel itself but in the basin now drained by the tunnel.