Lower Granite Lock and Dam

Lower Granite Dam
This congressionally authorized project consists of Lower Granite Dam, navigation lock, powerhouse, a fish ladder and associated facilities. The project provides hydroelectric generation, navigation, recreation and incidental irrigation. The dam, located at the upstream end of Lake Bryan, is about 3,200 feet long with an effective height of 100 feet. The dam is a concrete gravity type, with an earthfill right abutment embankment. It includes a navigation lock with clear dimensions of 86 by 674 feet; and an eight-bay spillway that is 512 feet long, with eight 50-foot by 60.5-foot radial gates.

Project Information

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 Project Fact Sheet



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



Construction began in July 1965 and was completed in 1984. The main dam is complete, as well as relocations and modifications to the Camas Prairie Railroad Bridge, state highways and county roads. The installation of the first three power-generating units was complete in 1975. Power came online for additional units four through six in 1979. Final modifications to the City of Lewiston’s water intake were completed in August 1987.


Lower Granite Dam

This congressionally authorized project consists of Lower Granite Dam, navigation lock, powerhouse, a fish ladder and associated facilities. The project provides hydropower, navigation, flood risk management, fish and wildlife habitat, recreation and incidental irrigation. The dam, located at the upstream end of Lake Bryan, is about 3,200 feet long with an effective height of 100 feet. The dam is a concrete gravity type, with an earthfill right abutment embankment. It includes a navigation lock with clear dimensions of 86 by 674 feet; and an eight-bay spillway that is 512 feet long, with eight 50-foot by 60.5-foot radial gates.



The powerhouse has six 135,000-kilowatt units. Power generated during fiscal year 2017 was 2.77 billion kilowatt hours.



The lake created by the dam extends upstream on the Snake River about 40 miles to Lewiston, Idaho, more than 460 river miles from the Pacific Ocean.


Adult Fish Passage

There is one fish ladder for passing migratory fish with entrances on both shores and a fish channel through the dam that connects to the south shore ladder. Modifications to improve adult Pacific lamprey passage include passage structures and installation of metal plating to assist lamprey upstream. Record hot weather in recent years created thermal barriers to adult fish migration. After testing a temporary solution in 2014 and 2015, the Walla Walla District constructed two permanent “intake chimneys” in 2016 to pump water from deep in the reservoir to cool the adult fish ladder and the adult fish trap built into the fish ladder.


Juvenile Fish Programs

As the first collector dam on the Snake River, Lower Granite is a primary component of the Juvenile Fish Transportation Program. Transport began in the late 1960s as a research program on how to bypass juvenile salmon and steelhead around U.S. Army Corps of Engineers (USACE) dams and reservoirs of the Snake and Columbia Rivers. The 10-year average collection of outgoing juvenile salmon and steelhead for 2011 to 2020 at Lower Granite was approximately 5.2 million fish with approximately 3 million of those transported via truck and barge below Bonneville Dam. A spillway weir was installed in 2001, resulting in improved in-river passage conditions for juvenile salmonids via the spillway. Additionally, improvements were made to the dam’s juvenile fish bypass system between 2014 and 2019. The upgrades include “daylighting” the below-ground fish-transportation piping from the dam to the juvenile fish facility by replacing it with an above-ground flume; remodeling gatewell orifice openings and the transportation channel inside the dam; replacing the dewatering unit and diverting excess water to new piping and valves that will enhance adult fish ladder attraction, emergency facility water supply, and fish trap water supply; and constructing a new bypass outfall pipe. The goal of the upgrades was improving juvenile fish survival and increasing operational reliability of the bypass and collection system.



The District constructed about 8 miles of levees around Lewiston to help protect lives and property from potentially destructive high-water conditions. Since construction, the levees have prevented more than $39.3 million in potential flood damages.



In fiscal year 2021, 1,492,539 tons of cargo passed through the navigation lock; the majority of the cargo consisted of grains, petroleum products, fertilizer, and wood products.



There are about 13,000 acres of project lands surrounding Lower Granite Lake. These project lands include fee lands that are federally owned and managed by USACE or are managed by lessees, as well as easement lands to which USACE has specific rights or easements (i.e., flowage or access). Most of these lands are used for wildlife habitat, wildlife mitigation, public recreation, and water-connected industrial development. There are 12 public boat launching facilities. In 2020, Lower Granite recreation areas hosted 1,912,325 visits.



More than 80 Walla Walla District employees work at the Lower Granite project. They serve as electricians, lock operators, mechanics, welders, riggers, painters, utility workers, heavy equipment operators, environmental resource specialists, biologists, park rangers, administrative support staff, engineers and maintenance workers. Together, they manage the safe and continuous operation of the project.



Lower Granite project lands provide opportunities for all sorts of recreational activities, including fishing, hunting, hiking, birding, camping, swimming and horseback riding. The Lower Granite Visitor Center offers a fish viewing room along with movies, interactive displays, guided tours, and a friendly and helpful staff. Amenities within the parks include boat launches, campsites, shelters, fire rings, picnic tables, restrooms, and playgrounds.


 Project Pertinent Data

Lower Granite Lock and Dam
Pertinent Data



State – Washington
County – Garfield and Whitman
River – Snake
River Mile – 107.5
Township – 14 N
Range – 43 E
Section – 32
Latitude – 46° 39' 37"
Longitude – 117° 25' 37"
River miles from mouth of Snake River - 107.5
River miles upstream from Little Goose Dam - 37.2
Owner - U.S. Army Corps of Engineers, Walla Walla District
Authorized Purpose - Power generation and inland navigation
Other Uses - Flood control (maintain levee freeboard at Lewiston), fishery, and recreation
Type of Project – Run-of-river


Real Estate:
Fee acquisition land above pool elevation 738 – 9,224 acres



Name - Lower Granite Lake1
Elevations (Feet Mean Sea Level):
Maximum at dam for spillway design flood – 746.5
Normal operating range at confluence gage (RM 139.5) – 738 to 733
Minimum at dam for standard project flood – 724


Length, miles:
Snake River (to Asotin damsite, RM 146.8) – 39.3
Clearwater River – 4.6
Length of shoreline - 91 miles
Average width - 0.3 miles
Maximum width - 0.6 miles
Surface area at elevation 738 (low flow, flat pool) - 8,900 acres
Storage below flat pool elevation 738 - 483,800 acre-feet
Storage below flat pool elevation 733 - 440,200 acre-feet
Storage between elevation 733 and 738 - 43,600
Height normal high pool to tailwater elevation 638 (low flow, 30,000 cfs or less) - 100 ft


Top width - 12 ft
Slopes, waterside and landside - 1V on 2H
Materials - Gravel and earth fill with impervious core
Top elevation - 5 feet above backwater profile for standard project flood
Embankment length:
Lewiston - 8.6 miles
Installed pumping capacity:
Lewiston levees 450.4 cfs


Dam (General) 
Axis (Lambert) - N 32° 00'E
Length and Widths, feet:
Dam total length at crest – 3,200
North abutment embankment -1,435
South non-overflow monoliths – 32.2
Spillway overall length – 512
Spillway to powerhouse non-overflow – 43.4
Powerhouse overall length – 656
Spillway to navigation lock non-overflow – 43.4
Navigation lock overall width at foundation – 304
Navigation lock overall width at deck – 186

Concrete Heights, feet:
Maximum overall concrete height (powerhouse sump deck to deck)
Maximum non-overflow monoliths height:
North - 151
Central - 166
South - 181
Maximum lock wall monolith height (culverts to deck) - 191


Deck elevations, feet msl:
Intake, Spillway Bridge, non-overflow sections, and upstream end of navigation lock - 751
Downstream end of navigation lock - 746
South shore fish ladder - 656
Tailrace and fishwater intake - 656
North abutment embankment - 756


Number of Bays - 8
Overall length (abutment centerlines) - 512 ft
Deck elevation - 751 ft msl
Ogee crest elevation - 681 ft msl
Flip lip elevation - 630

Control gates:
Type - Tainter
Size - 50'W x 60'H
Gantry crane (joint use with powerhouse) capacity - 100 tons
Stilling basin length - 188 ft
Stilling basin elevation - 580 ft msl
Maximum design capacity - 850,000 cfs



Length overall - 656 ft
Units 1 through 5 – 90 ft
Unit 6 – 96 ft
Erection and service bay – 110 ft
Width overall, transverse section - 243.17 ft
Intake deck elevation - 751 ft msl
Tailrace deck elevation - 656 ft msl
Maximum height (draft tube invert to intake deck) - 228 ft


Type - Kaplan, 6-blade
Runner diameter – 312 in
Revolutions – 90 per min
Rating – 212,400 horsepower
Distributor centerline elevation – 599


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

Net clear length, lock chamber - 674 ft
Net clear width, lock chamber - 86 ft
Upstream gate:
Type - Submersible tainter
Height - 23
Downstream gate:
Type - Miter
Height - 122 ft
Operating water surface elevations in chamber - 633 to 738
Maximum operating lock lift - 105 ft
Lift (riverflow 300,000 cfs, practical navigation limit) - 88.2 ft
Length of guidewalls (from face of gate):
Upstream (floating) – 750 ft
Downstream – 700 ft

Downstream approach channel: 
Width – 250 ft
Bottom elevation – 617
Minimum tailwater elevation - 633.0
Lower lock sill elevation - 618.0 ft
Upper lock sill elevation - 718.0 ft
Maximum depth over sills - 20.0 ft
Minimum depth over sills - 15.0 ft


Abutment Embankment

Embankment elevation - 756
Embankment top width - 45 ft
Material - Gravel fill with rock facing, impervious silt core
Upstream - Combination sand and gravel filters
Downstream - Gravel and sand filters
Slope, upstream - 1V on 2H
Slope, downstream - 1V on 2H


Fish Facilities2

Upstream migrants fish ladder:
Number of fish ladders - 1
Weir 634 to Weir 627 - 1V on 10H
Weir 728 to Weir 737 - 1 V on 32H
Ladder clear width – 20 ft
Design capacity – 75 cfs

Exit Channel:

Location - Width, feet Between weir 737 and pool in non-overflow section
Top of trashrack – El. 732
Invert – El. 727
Width – 6 ft

Alternative exit channel (pool elevation below 727):
Exit pipe to reservoir – 18-inch-diameter full plastic pipe down to El. 718,
and a half-round plastic pipe down to El. 710

Operating elevations:

Design range:
Pool elevations – 733 to 738
Tailwater elevations – 633 to 642
Riverflow – 0 to 225,000 cfs

Maximum operating range:

Pool elevations - 732 to 739
Tailwater elevations - 633 to 645.4
Riverflow - 0 to 340,000 cfs
Adult fish trap and handling facility - 1

Pumps for fishway system attraction water:
Number - 3
Capacity - 3,150 cfs

Downstream migrants bypass system:
Design pool range – 733 to 738
Design capacity – 200 to 250 cfs
Extended-length Submerged Bar Screens – 18
Vertical barrier fish screens – 18

Orifices from bulkhead and fish screen slots:
Number – 36, 36
Size (diameter in inches) – 10, 12
Fingerling collection gallery - 1
Fingerling transportation pipe – 1
Fingerling holding and sampling facility - 1

Fingerling transportation facilities:
Truck loading facility - 1
Barge loading facility - 1

Hydrologic Data

(Based on streamflow data for the Snake River near Clarkston, Washington)

Drainage area - 103,200 square miles
Period of Record - October 1915 to September 1972 (Discontinued in December 1972)

Instantaneous maximum of record, 29 May 1948 – 369,000 cfs
Instantaneous minimum of record, 2 September 1958 – 6,660 cfs\
Average annual flow – 50,300 cfs
Average annual mean daily peak flow – 188,300 cfs

Extreme outside period of record:
Flood of June 1894 – 420,000 cfs
Flood of June 1894, controlled by existing projects – 295,000 cfs
Standard project flood, controlled by existing projects:
Snake River below Clearwater River - 420,000 cfs
Snake River above Clearwater River - 295,000 cfs
Clearwater River above Snake River - 150,000 cfs

Spillway design flood - 850,000

Contact Us

Lower Granite Lock and Dam
885 Almota Ferry Road
Pomeroy, WA 99347-9758
Phone: 509-843-1493