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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
mile-long penstock conveying water to the Middle Fork powerhouse 7.5 to 9 feet in
diameter above the bifurcation and 5.5 feet in diameter below; and (6) the 62-foot by
154-foot Middle Fork powerhouse (11 miles downstream from the French Meadows
dam) that houses two Pelton-type units each having an authorized installed capacity of
61,200 kW, discharging tailrace waters into the Middle Fork interbay pool.
2.1.1.4 Ralston Development
The Ralston development is located on the Rubicon river and the Middle Fork and
includes: (1) the Middle Fork interbay dam (about 0.5 mile downstream of the Middle
Fork powerhouse) a 70.5-foot-high, 233-foot-long dam with a crest at elevation 2,536
feet; (2) the interbay pool that is less than 7 acres with 175 acre-feet of gross storage and
173 acre-feet of active storage; (3) a 23-inch-diameter instream flow maintenance pipe
conveying water to the Middle Fork with a maximum discharge capacity of 23 cfs; (4) a
60-inch-diameter low level outlet pipe with a maximum discharge capacity of 890 cfs;
(5) the 13.4-foot-wide, 6.7-mile-long horseshoe-shaped Middle Fork-Ralston tunnel
which routes water from the Middle Fork interbay pool to the Ralston powerhouse with a
maximum capacity of 836 cfs; (6) the Middle Fork-Ralston tunnel surge shaft and tank
located 500 feet from the tunnel outlet and consisting of a 10-foot-diameter surge shaft
and a 60-foot diameter by 22-foot high above-ground surge tank (8) a 1,670-foot-long, 8-
to 9.5-foot-diameter penstock leading to the Ralston power house; (9) the 82-foot by 90foot
Ralston powerhouse (located 30 miles downstream from the Hell Hole powerhouse
on the Rubicon River) that houses a Pelton-type unit with an authorized installed capacity
of 79,200 kW discharging tailrace waters to the Ralston afterbay on the Middle Fork; and
(10) the Ralston switchyard.
2.1.1.5 Oxbow Development
The Oxbow development is located on the Middle Fork and includes: (1) the
Ralston afterbay dam (located 9.5 miles downstream of the Middle Fork interbay pool),
an 89-foot-high, 560-foot-long dam with a crest at elevation 1,189 feet and a 232-footwide
gated ogee spillway with five 40-foot-wide radial spillway gates; (2) the Ralston
afterbay an 83-acre pool at elevation 1,177 feet with2,782 acre-feet of gross storage and
1,804 acre-feet of active storage of which 756 acre-feet is available to the Oxbow
powerhouse; (3) a 30-inch-diameter instream flow maintenance pipe conveying flows to
the Middle Fork with a maximum discharge capacity of 155 cfs; (4) a 72-inch-diameter
low level outlet pipe with a maximum discharge capacity of 1,132 cfs; (5) the Ralston-
Oxbow tunnel which connects the Ralston afterbay to the Oxbow powerhouse and
consisting of a 13.25-foot-wide, 403-foot-long horseshoe-shaped tunnel with a maximum
capacity of 1,088 cfs; (6) a 5-foot-long, 9-foot-diameter penstock leading the Oxbow
powerhouse; (7) the 60-foot by 98-foot Oxbow powerhouse that houses a Francis-type
unit with an authorized installed capacity of 6,128 kW discharging tailrace waters into the
Middle Fork; and (8) the Oxbow switchyard.
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