HomeMy WebLinkAboutMahoney Lake City of Saxton Alaska 1993AEA
MAHONEY LAKE
HYDROELECTRIC PROJECT
City of Saxman
Alaska
On March 12, 1993 the City of Saxman, Alaska, applied to the Federal Energy Regulatory Commission (FERC) for a preliminary permit for the proposed Mahoney Lake Hydroelectric Power project. The project is located on Revillagigedo Island, Alaska, and is within the Ketchikan Gateway Borough. It is approximately 6.5 miles from the City of Ketchikan. The Cape Fox Corporation is a participant in the project as the development agent for the City of Saxman.
The project would develop the water resources of Upper
Mahoney Lake to produce approximately 32,450 MWh per year for
the local community. The 32,450 MWh produced would meet the
near future power needs of the Ketchikan Gateway Borough. Ketchikan Public Utilities has projected a total community
power need of 175,631 MWh by the year 2000. This is 30,931 MWh more than the total generation of all existing hydroelectric facilities, KPU facilities and the Swan Lake
facility. This need is projected to be met through diesel
generation. The proposed project would eliminate the need
for diesel power generation. In addition, the project could be a significant power contributor on a regional power grid.
It would be a substantial source of power on the proposed Swan Lake - Tyee Lake intertie, adding to the flexibility to shift power to load centers within southern Southeast Alaska.
The power potential of the 1850 ft. drop in elevation between
Upper Mahoney Lake and Lower Mahoney Lake would be developed. The project site is located within the Ketchikan Ranger
District, Tongass National Forest and upon lands owned by the
Cape Fox Corporation. The 57 acre Upper Mahoney Lake is at elevation 1950. The project would be run of the river, with diverted flow to the turbine equaling inflow to the lake. The project as described below is based on a feasibility study being conducted by HDR Engineering, Inc. of Bellevue, Washington.
A small concrete faced rockfill dam, approximately 10 feet
high, would be constructed at the outlet of Upper Mahoney Lake. A 32" steel pipeline would extend through the dam
foundation into the lake and would serve as the submerged intake. The pipeline would extend downstream from the dam
about 500 feet along the creek to where it would turn to the right, drop into a 1500' vertical tunnel constructed using a raised bore and then through an 8' diameter 2700' long
horizontal tunnel to the proposed powerhouse.
The powerhouse would be an insulated metal building, 40' x 50', set on a cast in place reinforced concrete foundation
anchored into bedrock. It would house one 9 MW multi-jet
pelton turbine. The powerhouse would be located at the toe
of the slope near the waterfall, a barrier to anadromous
fish. Water from the powerhouse would be returned to the creek above anadromous fish habitat.
The project site would be accessed by a 5 mile extension of
the White River road, as shown on the attached map. The new
access road would be constructed on land owned by the Cape
Fox Corporation. The proposed 115 kV transmission line would run along the new road, along a short section of the existing White River road and then tie into the existing Swan Lake transmission line. A substation consisting of a main
transformer, 13 kV to 115 kV, and accessory switch gear would be required.
Three previous studies of the project have been conducted and are as follows:
a. Swan Lake, Lake Grace and Mahoney Lake Hydroelectric Projects Appraisal Report, for Ketchikan Public
Utilities, Ketchikan, Alaska, R. W. Beck and
Associates, Inc., June, 1977.
b. Draft Environmental Impact Statement Proposed
Mahoney Lakes Hydropower Project, Ketchikan, Alaska, Alaska District, U.S. Army corps of Engineers, 1978.
c. Future Hydropower Resources, Ketchikan, Petersburg, Wrangel and Quartz Hill, Appraisal Study, 1985 Update for Ketchikan Public Utilities, Ketchikan
Public Utilities, Ketchikan, Alaska, R. W. Beck and Associates, Inc., March, 1986.
The studies proposed construction of a hydroelectric power
facility at Mahoney Lake. They each presented and evaluated
a project based on a design somewhat different than the
project now proposed. As a result of these studies
considerable environmental work was performed in the project
area to characterize and assess the impact of the project, including fisheries studies, wildlife studies, sociological impact analysis and consultation with State and federal
agencies. There are no known cultural resources in the vicinity of the dam location. No threatened or endangered
species are known to occur in the vicinity of the project area. None of the land within the proposed project area is within a designated wilderness area, an area recommended for
wilderness designation, a wilderness study area or an area included in or designated for inclusion in the National Wild and Scenic Rivers System.
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