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Lower Monumental Lock and Dam

Lower Monumental Dam
This congressionally authorized project includes Lower Monumental Dam, powerhouse, navigation lock, two fish ladders, a juvenile fish facility (JFF), and appurtenant facilities providing for navigation, hydroelectric generation, recreation, and irrigation. The dam is located at the head of Lake Sacajawea, the reservoir created by Lower Monumental Dam. It is 3,791 feet long, with an effective height of about 100 feet. The dam is a concrete gravity-type dam, with earthfill abutment embankments.

Project Information

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Authorizations
The project was authorized by the River and Harbor Act of 1945.

Progress
Construction of the project began in June 1961, and it became operational in 1969. The entire project is considered complete. Construction of the additional generating units started in 1975, and was completed in 1981.

Project
The project includes Lower Monumental Dam, powerhouse, navigation lock, two fish ladders, a juvenile fish facility (JFF), and appurtenant facilities providing for navigation, hydroelectric generation, recreation, and irrigation.

Lower Monumental Dam
The dam is located at the head of Lake Sacajawea, the reservoir created by Lower Monumental Dam. It is 3,791 feet long, with an effective height of about 100 feet. The dam is a concrete gravity-type dam, with earthfill abutment embankments.

Reservoir
Lake Herbert G. West extends up the Snake River for a distance of 28.1 miles to the tailwater of Little Goose Dam. It has a surface area of 6,590 acres.

Generators
The powerhouse has six 135,000-kilowatt units. Power generated during fiscal year 2011 was 3.38 billion kilowatt hours.

Navigation Lock
This is a single-lift lock, 86 feet wide by 666 feet long, with a 100-foot vertical lift. About 1 million tons of commodities were passed through the navigation lock during 2011. The cargo primarily consisted of grains, petroleum products, fertilizer and wood products.

Fish Passage
There are two fish ladders for migrating adult salmon and steelhead to use. In 2007, a spillway weir was installed to improve conditions for juvenile fish passage at the dam. During 2011, more than 1,582,909 juvenile salmon and steelhead were collected at the Juvenile Fish Facility. About 207,024 fish were bypassed back into the river, and about 1,371,215 were transported for release past Bonneville Lock and Dam.

Lands
There are 8,335.5 acres of project lands surrounding Lake Herbert G. West. There are 7,024.0 acres of Corps-managed lands that are utilized for public recreation purposes, wildlife habitat, wildlife mitigation, and water-connected industrial development. Lake West offers seven day-use areas, five areas offering camping, five boat launch areas, and one designated swimming beach. Total visitation in 2011 at Lower Monumental’s recreation areas was 94,927.

People
About 50 Walla Walla District employees work at the Lower Monumental Project. They serve as electricians, lock operators, mechanics, welders, riggers, painters, utility workers, heavy equipment operators, biologists, park rangers, environmental resource specialists, administrative support staff, maintenance workers and engineers. Together, they manage the safe and continuous operation of the project.

Budget
During fiscal year 2011, total expenditures were about $9.5 million for the Lower Monumental Project.

References
Report of the Secretary of the Army on Civil Works Activities, Fiscal Year 2011.
General
Location:
State – Washington
County – Franklin and Walla Walla
River – Snake
River Mile – 41.6

River miles upstream from Ice Harbor Dam – 31.9
Owner – U.S. Army Corps of Engineers, Walla Walla District
Authorized Purpose – Power generation and inland navigation
Other Uses – Fishery and recreation
Type of Project – Run-of-river

Real Estate:
Fee acquisition land, acres 7,519

Reservoir
Name - Lake Herbert G. West
Elevations (Feet Mean Sea Level):
Maximum at dam for spillway design flood – 548.3
Normal operating range gauged at dam – 537 to 540
Length – 28.7 miles
Average width – 0.4 miles
Maximum width – 0.8 miles
Surface area at elevation 540 (low flow-flat pool) – 6,590 miles
Storage between elevation 537 and 540 – 20,000 acre ft

Dam (General)
Powerhouse, overall length - 656
Spillway, total length - 498
Navigation lock, overall width – 186

Concrete non-overflow sections:
Navigation lock to spillway (length) – 143 ft
Spillway to powerhouse (length) – 37 ft
Powerhouse to north shore embankment (length) – 228 ft
Earth embankment, north shore (length) – 968 ft
Earth embankment, south shore (length) – 1,075 ft

Total length of dam – 3,791 ft
Maximum height of concrete sections (foundations deck) – 256.7 ft
Maximum height of abutment section (North Shore foundation to top) – 154.8
Deck elevation – 553 ft msl
Top of abutment elevation – 558 feet msl

Spillway
Type - Ogee, concrete, gravity, gate controlled
Maximum width at base, elevation 392 feet msl - 152 ft
Maximum height, foundation to deck - 152 ft
Number of bays - 8
Overall length (abutment centerlines) - 512 ft
Clear length - 400 ft
Crest elevation - 483 ft msl
Gate seal elevation - 481.44 ft msl
Top of gate in closed position, elevation - 542
Deck elevation - 553 ft msl
Gate lip elevation at maximum opening - 535 ft msl

Control gates:
Type - Tainter
Size - 50'W x 60'H
Method of operation - Individual electric hoists, remote controlled

Maintenance closure for spillway bays - Stoplogs
Spillway design flood:
Peak discharge - feet 850,000 cfs
Pool elevation - 548.3 ft msl
Tailwater elevation - 465.1 ft msl
Gross head - 83.2 ft

Maximum flood at normal pool, elevation 540
Discharge - 676,000 cfs
Tailwater elevation - 460.5 ft msl

Stilling basin:
Type – Horizontal apron
Width, perpendicular to flow – 498 ft
Length, parallel to flow - 180 ft
Floor elevation - 392 ft msl
Height of continuous end sill - 13 ft

Powerhouse
Number of generating units - 6
Spacing:
Units 1 through 5 - 90
Unit 6 - 96
Erection and service bay - 110

Turbines:
Type – Kaplan 6-blade
Runner diameter – 312 in
Revolutions - 90 per minute
Rating - 212,400 horsepower
Generators:
Rating (nameplates) - 135,000 kilowatts
Power factor - 0.95
Kilovolt ampere rating - 142,100

Units installed complete initially - 3
Skeleton units provided initially - 3
Total units now installed - 6
Plant capacity, nameplate rating - 810,000 kilowatts

Crane capacities:
Intake (joint use with spillway) – 100 tons
Bridge – 600 tons
Draft tube gantry – 50 tons

Navigation Lock and Channels
Type - Single lift
Net clear length, lock chamber - 650 ft
Net clear width, lock chamber - 86 ft
Minimum water depth over stills - 15 ft

Upstream gate:
Type - Vertical lift
Height - 22 ft

Downstream gate:
Type - Vertical lift
Height - 84.08 ft

Maximum operating lock lift - 103.00 ft
Normal fill time - 11.3 minutes
Normal emptying time - 13.3 minutes


Fish Facilities
Number of fish ladders - 2
Slope - 1V on 10H
Number of weirs (including orifice-control section) - 103

Overflow weirs:
Number - 97
Height - 6 ft
Orifice size - 18 x 18 in

Exit of ladders, invert elevation - 530.5 ft msl
Entrance of ladder, invert elevation - 429 ft msl
Normal fishway flow, forebay to each ladder - 74 cfs
Ladder clear width - 16 ft
Pumps for fish attraction water:
Number - 3
Type - turbine
Capacity - 835 cfs
Forebay water required for each turbine - 65 cfs

Fishway entrances:
North shore - 2
South shore - 3
Non-overflow - 3

Powerhouse collection system:
Number of orifice entrances
Length of channel - 10 ft
Width of channel - 17.5 ft

Fingerling bypass system:
Collection system openings per gate slot - 1
Size of collector pipes – 6 in
Forebay water required (per powerhouse unit) - 2.4 cfs

Hydrologic Data
(Based on streamflow data for the Snake River near Clarkston, Washington)
Drainage area - 103,200 sq miles
Period of record - Oct 1915 to Sep 1972
(Discontinued in Dec 1972)

Discharges in cubic feet per second:
Instantaneous maximum of record, 29 May 1948 - 369,000
Instantaneous minimum of record, 2 Sep 1958 - 6,660
Average annual flow - 50,300
Average annual mean daily peak flow - 188,300

Extreme outside period of record:
Flood of June 1894 - 409,000
Flood of June 1894, controlled by existing projects - 295,000

Standard project flood (controlled by existing projects):
Snake River below Clearwater River - 420,000
Snake River above Clearwater River - 295,000
Clearwater River above Snake River - 150,000

Spillway design flood - 850,000

Contact Us

Lower Monumental Lock and Dam
5520 Devils Canyon Road
Kahlotus, WA 99335
Phone: 509-282-3219

Lower Monumental Recreation

Lower Monumental