Draft EIS_072312.pdf - Middle Fork American River Project ...

20120723-4002 FERC PDF (Unofficial) 07/23/2012
45-foot by 68-foot French Meadows powerhouse housing a Francis-type unit with an
authorized installed capacity of 15,300 kW discharging tailrace water to the Middle Fork;
and (6) the French Meadows switchyard.
2.1.1.2 Hell Hole Development
The Hell Hole development is located southwest of the French Meadows
development on the Rubicon River and includes: (1) the 410-foot-high, 1,570-foot-long
Hell Hole dam with a crest at elevation 4,650 feet and a 350-foot-wide uncontrolled
spillway; (2) the 1,253-acre Hell Hole reservoir at elevation 4,630 feet with 207,590 acrefeet
of gross storage and 205,057 acre-feet of active storage; (3) an outlet tunnel that
leads to a 16-inch-diameter instream flow maintenance pipe conveying flows to the
Rubicon River with a maximum discharge capacity of 20 cfs and a 48-inch-diameter low
level outlet pipe conveying flows to the Rubicon River or to the powerhouse penstock
with a maximum discharge capacity of 852 cfs; (6) a 100-foot-long, 48-inch to 20-inchdiameter
penstock conveying water from the low level outlet pipe to the powerhouse; and
(7) the 24-foot by 26-foot Hell Hole powerhouse that houses a Francis-type unit with an
authorized installed capacity of 725 kW discharging tailrace water to the Rubicon River.
2.1.1.3 Middle Fork Development
The Middle Fork development is located on the Middle Fork and on two
tributaries (North Fork and South Fork) of Long Canyon Creek (a tributary of the
Rubicon River) and includes: (1) the North Fork Long Canyon Creek diversion
consisting of: (a) a 10-foot-high, 120-foot-long diversion dam with a crest at elevation
4,720 feet; (c) a 12-inch-diameter instream flow maintenance pipe conveying water to the
North Fork with a maximum discharge capacity of 2 cfs; (d) a 36-inch-diameter low level
outlet pipe with a maximum discharge capacity of 100 cfs; (e) a conveyance structure that
routes water from the diversion to the Hell Hole-Middle Fork tunnel consisting of a 36inch-diameter,
0.7-mile-long buried steel pipe, a 403-foot-long, 6-foot-diameter vertical
shaft, and a 54-foot-long tunnel with a maximum capacity of 100 cfs; (2) the South Fork
Long Canyon Creek diversion consisting of (a) a 27-foot-high, 145-foot-long c diversion
dam with a crest at elevation 4,650 feet and a 60-foot-long uncontrolled ogee spillway;
(c) a 12-inch-diameter instream flow maintenance pipe conveying flows to the South
Fork with a maximum discharge capacity of 5 cfs; (d) a 36-inch-diameter low level outlet
pipe with a maximum discharge capacity of 140 cfs; (e) conveyance structure that routes
water from the diversion to the Hell Hole-Middle Fork tunnel and consisting of a 42inch-diameter,
50-foot-long buried steel pipe, a 387-foot-long, 6-foot-diameter vertical
shaft, and a 27-foot-long tunnel with a maximum capacity of 200 cfs; (3) the Hell Hole-
Middle Fork tunnel that routes water from the Hell Hole reservoir to the Middle Fork
powerhouse penstock and is a 13.4-foot-wide, 10.4-mile-long, horseshoe-shaped tunnel
with a maximum capacity of 920 cfs; (4) the Hell Hole-Middle Fork tunnel surge shaft
and tank located 1,800 feet from the tunnel outlet and consisting of an 8-foot-diameter
surge shaft and a 60-foot diameter by 22-foot high above-ground surge tank; (5) a 07-
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