Before the FERC Application for New License for the Annex Creek ...

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2.0 ANNEX CREEK COMPONENT DESCRIPTION
2.1 GENERAL
The Annex Creek Component iss i tuated ina remote area of the
Tongass National Forest. There are two lakes in the Annex Creek drainage
area, Upper and Lower Annex Lake. Upper Annex Lake Reservoi r, the 1 arger of
the two, serves as the reservoi r for the Annex Creek Component. It has a
natura 1 water surface area of 183 acres at El 820 Mean Sea Leve 1 (MSL). A
timber buttress dam is located at the outlet of Upper Annex Lake Reservoir,
with a spillway crest at El 844.3 MSL. This raises the normal maximum water
surface area of the reservoi r to 264 acres. Spi 11 way dis charge flows into
Lower Annex Lake whi ch ; s drai ned by Annex Creek. Annex Creek flows for
approximately 0.5 mile downstream of the lake, discharging into Taku Inlet.
A tunne 1 has been dri ven in rock to Upper Annex Lake Reservoi r,
with a lake tap at El 690 MSL. A valve chamber is located at the outlet of
the tunnel which connects to the penstock. The penstock is a riveted steel
pipe 7,031 feet long, varying in diameter from 42 to 34 inches. The powerhouse
conta ins two turb i ne-genera tor un its for a tota 1 of 4,050 kVA and i s
located at Taku Inlet, approximately 0.5 mile northeast of the outlet of Annex
Creek. A 23-kV transmission line, with a combination of steel and wood structures,
transmi ts the power generated at Annex Creek to the Thane Sw; tchyard.
Thane is located on Gastineau Channel, approximately 4 mi les southwest of
downtown Juneau.
2.2 PROJECT STRUCTURES
Annex Creek Dam. The Annex Creek Dam is a 20-foot-high by approximately
110-foot-long timber buttress dam, which was reconstructed in 1967. The dam
is constructed of pressure treated timbers. The upstream face is composed of
3-inch-thick tongue and groove decking over 8-inch by 8-inch horizontal
stringers. The stringers are supported by 8-inch by 10-inch beams which rest
on 8-inch by 10-inch timber buttress struts. The upstream face is protected
with an application of coal tar pitch. The toe of the dam is a concrete curb
which provides a watertight seal with the rock foundation.
A 57-foot-long spillway crest, also constructed of timber decking,
is supported by 8-i nch by 8-i nch braced timber col umns at the center of the
dam crest. The spillway crest is at El 844.3 MSL. The total hydraulic capacityof
the spillway at Annex Dam is approximately 458 cfs with no freeboard on
the dam.
Annex Creek Power Conduit. The Annex Creek Tunnel is 1,418 feet long and
connects directly with Upper Annex Lake Reservoir via a lake tap at El 690
MSL. The 1 ake tap is not prov i ded wi th trashracks. The tunne 1 is approximately
8 feet by 8 feet and is unlined at the upstream end for approximately
540 feet, then protected by a 2-i nch guni te cover; ng for the next 628 feet.
Approx i ma te 1 y the 1 as t 250 feet of the tunne 1 are re i nforced concrete-1 i ned.