SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND HAER ID-45-C PENSTOCK /0-45-C North Bank of Snake River, at West end of Intake Tipperary Corner vicinity Jerome Idaho

PHOTOGRAPHS

WRITTEN HISTORICAL AND DESCRIPTIVE DATA

HISTORIC AMERICAN ENGINEERING RECORD PACIFIC WEST REGIONAL OFFICE National Park Service U.S. Department of the Interior 1111 Jackson Street, Suite 700 Oakland, CA 94607 HISTORIC AMERICAN ENGINEERING RECORD SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK p,~9 HAER NO. ID-45-C

Location: The tunnel is attached to the west end of the Intake (HAER NO. ID-45-B), at the westernmost capture point of the Shoshone Falls Project. The tunnel trends to the northwest from the Intake, emptying into the penstock above and east of the powerhouses. The penstock extends northwesterly from the west end of the tunnel, decreasing in elevation along its course to where it branches into three pipes that feed the three generators of the powerhouses.

USGS Twin Falls, Idaho Quadrangle, ~ 1'. 'f\t i.\ UTM Coordinates: Tunnel (east end): 713114mE, 4719344mN; Penstock (west end): 712953mE, 471941 lmN.

Dates of Construction: 1901-1921

Engineer: 1901 Tunnel Design: R.W. Faris (Shoshone Falls Power Company Ltd.); 1904 Tunnel Completion: Richard S. Cookinham (Chief Engineer, Great Shoshone & Twin Falls Water Power Co.); 1921 Penstock: W.G. Hamilton (Sponsor Engineer, Electric Bond & Share Co.).

Builder: 1901 Tunnel Construction: R.W. Faris (Shoshone Falls Power Company Ltd.); 1904 Tunnel Construction: William H. Barry/Barry Construction Company, Chicago; · 1921 Penstock Construction: Phoenix Construction Company, Phoenix

Present Owner: Idaho Power Company 1221 West Idaho Street Boise, Idaho 83702

Present Use: Hydroelectric Power Generation

Significance: The concrete-lined tunnel was among the first, if not the first, permanent components of the Shoshone Falls Project. Begun in 1901, it took more than three years and several changes of SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 2)

ownership before the tunnel was complete. The current penstock, installed in 1921 to replace the original penstock, is an original component of the 1920s expansion of the Project. The larger penstock with three diversion tubes was necessary in order to feed the additional generator installed in the 1921 powerhouse as part of the Project's expansion. The tunnel and penstock are the primary features that make power generation at the Shoshone Falls Hydroelectric Project possible as they are the sole features that could be constructed to take advantage of the 212-foot drop from the top of Shoshone Falls to the bottom in an area of extreme topographic constraints.

Historian: Sheri Murray Ellis, May 2007. James W. Steely, May 2007.

Project Information:

Between May and December 2007, SWCA Environmental Consultants documented the hydroelectric complex, under guidance of the Historic American Engineering Record (HAER). Project manager Sheri Murray Ellis (SWCA) coordinated with historian and photographer James W. Steely to complete the HAER documentation. Archives for the Shoshone Falls Hydroelectric Project are located at the Idaho Power Company (IPC) headquarters in Boise, Idaho, and at the public library in Twin Falls, Idaho. Records from the IPC archives were provided to SWCA by Mr. Shane Baker, Senior Archaeologist for IPC. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 3)

Historic and Engineering Context:

The Shoshone Falls Hydroelectric Project 1) encompasses a unique tunnel and penstock system that was constructed with great effort in a remote landscape; 2) was adapted to the severe environmental constraints created by the deep and narrow Snake River Gorge; 3) captured a natural water source and used innovative design methods to generate substantial hydroelectric power out of a precipitous elevation change in the Snake River; 4) is an early and enduring example of a high-head hydroelectric complex in Idaho; 5) made significant contributions to the development and expansion of the electrified irrigation system of the Twin Falls/Magic Valley region; and 6) has operated continuously for at least 100 years.

Additionally, the facility has made significant contributions to the development and maintenance of the local tourism industry; Idaho Power Company, current operator of the hydroelectric project, has entered into an agreement with local municipalities to provide a minimum of 300 cubic feet per second of water flow over Shoshone Falls, a popular tourist site, during the yearly tourist season.

Character Defining Attributes

The power tunnel is an underground structure that was not available for visual inspection as part of the documentation. As such, the description provided here is based upon design drawings, historical photographs, and archival documents. A portion of the penstock is visible above ground, and the description herein is based upon first-hand visual inspection and historical photographs and documents.

The power tunnel begins at the intake near Dam #1 and extends to the northwest below ground on an approximately 15- Overview of penstock (at left); view to the south from cliff degree downward angle. The tunnel, above powerhouse complex. Photo taken May 2007. which is lined with concrete and has an arched crown, measures approximately 440 feet long by 10 feet 6 inches tall by 10 feet 6 inches wide. 1 It has a flow area of approximately 92.5 square feet. 2

The penstock measures approximately 120 feet long and is 10 feet in diameter. It overlaps with (is inserted into) the tunnel for approximately 20 feet. The penstock is constructed of riveted

1 Idaho Power Company. 1919. Drawing 254031, General Elevation of Present Shoshone Falls Power Station. Idaho Power Company, Boise. 2 Idaho Power Company. n.d. Exhibit A. Description of Project, Shoshone FERC Project NO. 2778. Idaho Power Company, Boise. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 4) steel plates and rests on a cast-in-place concrete saddle. It is anchored to the tunnel portal and the powerhouse complex with large concrete blocks.

Concrete block anchor at base of penstock. Note concrete saddle supporting penstock pipe and riveted steel construction ofpenstock. Photo taken May 2007.

Reconstruction of tunnel entrance at Intake ca. 192 l. Dam #1 at left. Photo courtesy of Idaho Power Company. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 5)

Original 1907 penstock immediately prior to Penstock saddle and tunnel portal after removal 1921 replacement. Photo courtesy ofldaho Power of 1907 penstock during 1921 expansion. Photo Company. courtesy of Idaho Power Company. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 6)

Tunnel portal with penstock pipe outlet in 1921, prior to construction of the new penstock. Photo courtesy of Idaho Power Company.

Transporting segment of new penstock pipe to construction site in 1921. Photo courtesy of Idaho Power Company. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 7)

Transporting segment of new penstock pipe to construction site in 1921. Photo courtesy of Idaho Power Company.

Construction of new penstock in 1921, prior to completion of new powerhouse expansion. Photo courtesy of Idaho Power Company. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 8)

Construction of new penstock in 1921. Photo Construction of new penstock in 1921. Photo courtesy of Idaho Power Company. courtesy of Idaho Power Company. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 9)

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Conceptual design drawing of east half tunnel/penstock. Adapted from original drawing. Not to scale. SHOSHONE FALLS HYDROELECTRIC PROJECT, TUNNEL AND PENSTOCK HAER NO. ID-45-C (Page 10)

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Conceptual design drawing of west half tunnel/penstock. Adapted from original drawing. Not to scale.