Almanor Dam (Canyon Dam) and Lake Almanor

General Notes
 

Construction of Almanor Dam was started by the Great Western Power Company¹ in 1910 in order to provide water storage for Big Bend Powerhouse, located upstream from Oroville, and irrigation in the central valley.  While Big Bend Powerhouse was later flooded by Lake Oroville, Lake Almanor now provides water storage for six Pacific Gas and Electric Co. hydro-electric plants² located downstream on the North Fork of the Feather River as well as for irrigation.
 

Originally conceived as a masonry dam, Almanor Dam was constructed as an earth dam when poor foundation conditions were encountered.  The name "Almanor" was created by combining  the names of the three daughters of Great Western Power Company's Vice-President Guy C. Earl - ALice, MArtha, and ElaNOR.  The Great Western Power Company also formed a subsidiary know as the Western Canal Company to distribute irrigation water to farmers west of Oroville.  The Western Canal Water District continues to hold water rights that require water be released from Lake Almanor (and other smaller PG&E reservoirs located in the Feather River watershed) during the irrigation season (March 1 through October 31).

Water is normally released through the Prattville Tunnel for power generation at Butt Valley Powerhouse,  Caribou Powerhouse, and Belden Powerhouse and other plants downstream as well as irrigation.  The tunnel outlet is located on the west shore of Lake Almanor at Prattville where two outlet towers can be seen.  The northward tower is the entrance for the Prattville Tunnel.  The southward tunnel, used before Butt Valley Powerhouse was constructed, is now plugged.  During some wet years, water is also released through the outlet tower located just upstream of the dam.

• River diverted:  North Fork Feather River
• Year completed:  1914, raised in 1927, raised in 1962
• Maximum storage elevation:  4494 feet (PG&E datum, see General Notes)
• Volume of lake at maximum storage:  1,142,964 acre-feet
• Maximum reservoir surface area:  28,257 acres
• Maximum dam height:  130 feet
• Crest length:  1,250 feet
• Spillway elevation:  4,500 feet³
• Drainage Area:  503.0 square miles
• Maximum outlet tower flow:  2,000 cfs (approximate)
• Maximum flow through Prattville Tunnel:  2,118 cfs

Notes:

1. Great Western Power Company was merged into PG&E in 1930.
2. Butt Valley Powerhouse, Caribou #1 and #2 Powerhouses, Belden Powerhouse, Rock Creek Powerhouse, Cresta Powerhouse, and Poe Powerhouse.
3. Because the spillway is six feet above the maximum storage operating level, the spillway is never used.  Instead, when necessary to not exceed the maximum storage level, water is released through the outlet tower located just upstream of the dam. 

Lake Almanor Storage Curve

Lake Almanor Area Curve

Butt Valley Dam

Constructed by the Great Western Power Company starting in 1919 to provide water storage for Caribou Powerhouse.  A dinky engine, used in original construction of the dam was discovered in 1997 when the reservoir was drained for repair work.  It had been submerged for about 70 years.  The restored dinky engine is now on display on Highway 36 on the west end of Chester.

• River diverted:  Butt Creek
• Year completed:  1924
• Maximum storage elevation:  4132.0 feet (PG&E datum)
• Volume of lake at maximum storage:  49,891 acre-feet
• Maximum reservoir surface area:  1,600 acres
• Maximum dam height:  84 feet
• Crest length:  1,370 feet
• Spillway elevation:  4,132.1 feet
• Drainage Area:  86.2 square miles

Belden Dam (Caribou Afterbay Dam)

Constructed by PG&E in 1958, the dam diverts water released from Butt Valley reservoir to Belden Powerhouse.

• River diverted:  North Fork Feather River
• Year completed:  1958
• Maximum storage elevation:  2,975.5 feet (PG&E datum)
• Volume of lake at maximum storage:  2,477 acre-feet
• Maximum reservoir surface area:  42 acres
• Maximum dam height:  84 feet
• Crest length:  400 feet
• Spillway elevation:  2,960.5 (bottom of radial gate)
• Drainage Area:  616 square miles

Mountain Meadows Dam (Indian Ole Dam)

Originally constructed in 1924 and later reconstructed in 1962, Mountain Meadows dam and reservoir provides storage for Hamilton Branch Powerhouse which is located on the east shoreline of Lake Almanor.  The dam and powerhouse are currently without a FERC license since no license is currently required by federal regulations.  Mountain Meadows reservoir is sometimes referred to locally as Walker Lake.

• River diverted:  Hamilton Creek
• Year completed:  1924, reconstructed in 1962
• Maximum storage elevation:  5,030.4 feet (PG&E datum)
• Volume of lake at maximum storage:  24,800 acre-feet
• Maximum reservoir surface area:  5,800 acres
• Maximum dam height:  26 feet
• Crest length:  264 feet
• Drainage Area:  158 square miles

Butt Valley Powerhouse

• Year completed:  1958

• Normal maximum gross head:  362 feet

• Maximum flow:  2,118 cfs

• Dependable capacity:  41 MW

• Average annual energy:  156.1 GWh 

• Annual plant factor:  43%

Caribou #1 and #2 Powerhouses

Caribou #1

• Year completed:  1921

• Normal maximum gross head:  1,150 feet

• Maximum flow Caribou #1:  1,114 cfs

• Dependable capacity:  75 MW

• Average annual energy:  171.4 GWh

• Annual plant factor:  26 %

Caribou #2

• Year completed:  1958

• Normal maximum gross head:  1,150 feet

• Maximum flow:  1,464 cfs

• Dependable capacity:  120 MW

• Average annual energy:  442.2 GWh

• Annual plant factor:  42 %

Notes:

1. Each powerhouse is operated independently from the other.  Normally the newer and more efficient Caribou #2 is operated in favor of the older Caribou #1.  When power demands are high, both powerhouses are operated together.

Belden Powerhouse

• Year completed:  1969

• Normal maximum gross head:  770 feet

• Maximum flow:  2410 cfs

• Dependable capacity:  125 megawatts MW

• Average annual energy:  395.5 GWh

• Annual plant factor:  36%

Oak Flat Powerhouse

Oak Flat Powerhouse was constructed to generate power from the fish water released from Belden Dam.

• Year completed:  1985

• Normal maximum gross head:  84 feet (approx)

• Maximum flow:  140 cfs (matches maximum fish release)

• Dependable capacity:  1.3 MW

• Average annual energy:  6.7 GWh

• Annual plant factor:  59 %

Hamilton Branch Powerhouse

• Year completed:  1921
• Normal maximum gross head:  410 feet
• Maximum flow:  200 cfs
• Normal operating capacity:  4.8 MW
• Average annual energy:  26.1 GWh

General Notes

1. Elevations use PG&E datum which is 10.2 feet less than  United States Geological Service (USGS) datum.  Add 10.2 feet to PG&E elevations to determine USGS elevations.

2. Normal maximum gross head:  Height that reservoir is above the power plant.  (e.g. elevation of reservoir - elevation of power plant).

3. Dependable capacity:  Operating capacity during the summer of a dry year.

4. Average annual energy is based on past 25 years of record.

5. Annual plant factor:  Percentage of time plant was fully loaded based on operating data for the past 25 years.

6. Acre-feet:  One acre-foot equals 43,560 cubic feet or 325,851 gallons.

7. cfs:  cubic feet per second.

8. MW:  Mega-Watt  equals 1,000,000 watts or 1,000 kilowatts.

9. GWh:  Giga-Watt-hour equals 1,000,000  kilowatt-hours.