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

E-5
Project 11 cense, because of safety cons i derations. (See Dam Safety Report,
included in the Supporting Design Documentation to Exhibit F.) Water from the
Salmon Creek Dam is conveyed downstream to the Upper Powerhouse via the
4,475-foot-long steel Upper Penstock. Before reaching the powerhouse, however,
the penstock bi furcates perm; tti ng water to be di verted to the Upper
Powerhouse (2.8 MW) or to the 11,030-foot-long Lower Penstock which leads to
the Lower Powerhouse (6.7 MW). The flow is controlled by two butterfly
va 1 ves. Because the same penstock serves both powerhouses, they cannot be
operated simultaneously. The Upper Powerhouse contains two 2,500-horsepower
i mpul se turbi nes connected to 2, 300-Vo 1 t generators. The Lower Powerhouse
contains one 9,210-horsepower impulse turbine connected to a 12,700-Volt generator.
An arbitrary elevation datum was used for the Salmon Creek Dam and
Upper Powerhouse when they were constructed. This arbitary datum is
26.29 feet below Mean Lower Low Hater (MLLW) and fixes the dam spillway crest
at El 1172. Throughout this exhibit this datum will be referred to as the
Upper Salmon Creek Datum (USCD).
The Lower Penstock and Lower Powerhouse used an elevation datum
4.79 feet below MLLW. This arbitrary datum w1l1 be referred to as the Lower
Salmon Creek Datum (LSCD).
1 • 3 • 2 C 1 i rna t e
Typical climatic conditions of Southeast Alaska are discussed in
Section 1.1.2. Temperatures at the Salmon Creek Component are similar to
those measured in downtown Juneau.
The mean temperature in downtown Juneau ranges from 42°F to
61°F in summer, and 18°F to 34°F in the winter. Precipitation data
recorded by Alaska Gastineau Mining Company at the Salmon Creek Dam and Upper
Powerhouse, and data from nearby Gold and Sheep creeks i nd i cate that annua 1
precipitation at Salmon Creek is 100-150 inches, most of which falls during
the months of October to December (AELP, 1982>' Total yearly precipitation in
the Upper Sa 1 mon Creek dra i nage is 15 to 35'1 greater than that in downtown
Juneau, which receives a mean annual precipitation of 91 inches.
Snow occurs frequently in the area, but usually melts quickly at
lower elevations. Higher elevations often remain snow covered unti 1 early
summer. The average snowfall in downtown Juneau, based on a 31-year period of
record, is 107 inches.
1.3.3 Topography, Vegetation, and Hetlands
The topographic setting of the Salmon Creek Reservoir is very
similar to that of Annex Creek. The Salmon Creek drainage basin ranges in
elevation from sea level to 4935 feet at Observation Peak located northeast of
the reservoi r. The hi gher elevations of the watershed are character; zed by
exposed bedrock and alpine tundra vegetation, and the terrain is precipitous.