Mill Creek Dam and Bennington Lake

The Mill Creek Flood Control Project consists of the Diversion Dam, intake canal, Bennington Lake, Mill Creek Storage Dam, Russell Creek canal, Mill Creek return canal, and the Mill Creek Channel. Construction of the dam and its associated works was completed in 1942.

When flows through Mill Creek rise too high, the Diversion Dam diverts the excess, via the intake canal, into Bennington Lake, which is impounded by Mill Creek Storage Dam. Mill Creek Storage Dam is an earth-fill structure with a heavy gravel face. It is 800 feet wide at the base, 125 feet high and 3,200 feet long at the crest. After a high-water event, water in Bennington Lake is released via the Russell Creek canal and the Mill Creek return canal. Water that is not diverted into the lake travels down the Mill Creek Channel, through the middle of the city.


On March 31, 1931, an estimated 6.65 inches of intense rainfall created what was termed “the worst flood in Walla Walla’s history.” The floodwaters resulted in extensive damages throughout the city. This flood, and concerns over the reoccurring nature of Mill Creek’s floods, prompted Virgil B. Bennington, then President of the Walla Walla Chamber of Commerce, to lobby the U.S. Congress for flood protection. The project was authorized by the Flood Control Act of 1938.

Bennington Lake

This off-stream reservoir has a maximum storage capacity of 8,300 acre-feet for flood control. It also provides a variety recreation opportunities, including hiking, fishing, hunting, boating and picnicking.

In the spring, water is diverted from Mill Creek to Bennington Lake once the risk of flooding is over. The lake is stocked with rainbow trout by the Washington Department of Fish and Wildlife.

Boating on the lake is limited to paddling, rowing, wind power, or vessels with electric motors. No gas engines are allowed on the water at any time. This policy protects the lake from unwanted pollutants associated with gasoline-operated motors and provides maximum space for vessels compatible with the lake’s small size.

Picnic tables, shelters and restrooms are available at the lake parking lot. There is also a life jacket loaner board to help keep everyone safe on the water.

Hunting is permitted around Bennington Lake, subject to Washington State regulations, in the areas designated on the map.

The Bennington Lake area is open year-round 5 a.m. to 10 pm.

Mill Creek Channel

About 5,000 feet of the Mill Creek channel is federally operated and maintained. The locally operated portion of the channel begins at the Mill Creek-Bennington Lake unit and extends six miles through the city of Walla Walla.

Rooks Park

Rooks Park offers visitors a wide variety of recreational opportunities. The 18-acre park includes a reservable picnic shelter, sand volleyball court, playground, horseshoe pit, group fire rings, picnic sites with tables, BBQ grills and accessible restrooms. Large open areas allow for football and soccer games, while small, secluded areas provide a quiet place to enjoy the outdoors. The park is open from 7 a.m. until posted closure hours, sunset. The entrance is open year-round to walk-in traffic, but seasonally closed to vehicles from October 15 to April 1 with reduced amenities.

To reserve the Rooks Park Shelter visit or call 1-877-444-6777.

** All areas are day use only, no overnight stays or camping**


Project Information

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 Project Pertinent Data
Official Name: Mill Creek, Washington*
U.S. Army Corps of Engineers Reference: Mill Creek Project

State - Washington
County - Walla Walla
Stream - Mill Creek

Construction Completion Dates:
Dam and appurtenant works - 1942
Mill Creek Channel - 1949

Owner: U.S. Government
Managers: U.S. Army Corps of Engineers and Mill Creek Flood Control Zone District
Authorized purposes: Flood control and recreation
Type of Project: Channelization and off-stream storage
**Real Estate: 611.46 acres of fee lands and 87.27 acres of easement lands

Federally-Owned Units
Diversion Works
Diversion Dam:

Type - Ambursen, ogee crest
Length at crest - 250 ft
Crest elevation - 1261
Height - 14 ft
Design discharge, cs (with water surface elevation 1268) - 17,000
Concrete structure top elevation - 1270
Stilling basin length - 24 ft
Stilling basin invert elevation - 1245
Type - Radial sluice gate
Size - 6x8 ft
Number - 1
Sill elevation - 1247
Control - Manual, with portable engine drive
Maximum allowable discharge - 400 cfs

Fish Ladder:
Width - 6.5 ft
Capacity - 42 cfs
Operating range elevation - 1253 to 1256
Intake invert elevation - 1250.25
Exit invert elevation - 1245
Stilling Basin:
Length - 4 ft
Width - 19.5 ft
Floor elevation - 1242
End sill elevation - 1244

Diversion Levee:
Type - Earthfill with heavy gravel face
Crest elevation - 1270 to 1280 ft
Length at crest - 2,200 ft
Top width - 12 ft
Maximum height - 23 ft
Design freeboard (standard project flood) - 5 ft

Debris Facilities
Debris Barriers:
Location - Diversion Dam forebay
Length - 550 ft
Type - Steel crib and cable

Shear Wall:
Location - Headworks Intake Canal
Length - 90 ft
Type - Panel

Intake Canal Facilities
Type - Concrete non-overflow with radial gates
Gate size – 8x18 ft
Number - 4
Sill elevation – 12,525
Control - Manual (optional use of portable electric operator)

Intake canal end, elevation - 1,250
Invert elevation - 1,252
Capacity - 7,000 cfs
Intake canal base width - 80 ft
Intake canal length - 1,800 ft

Off-Stream Storage Reservoir (Virgil B. Bennington Lake)
Name: Virgil B. Bennington Lake***
Maximum pool elevation for flood control - 1,265
Capacity at elevation 1265 – 8,300 acre-feet
Maximum allowable time for storage above elevation 1235 (due to stoppage) - 15 days
Capacity at elevation 1235 – 3,300 acre-ft

Storage Dam (Mill Creek Dam)
Type: Earthfill with heavy gravel face
Crest elevation - 1,270
Length at crest - 3,200 ft
Top width - 20 ft
Height above valley floor - 1,150 ft
Toe of embankment, elevation - 1,215
Maximum width at base - 800

Embankment Toe drains:
Date nine wells rehabilitated, year - 1,979
Drainage discharge header, elevation - 1,135
CP manhole diameter - 48 in

Outlet Works
Intake Tower:
Slide gate, centerline elevation - 1179
Intake tower, weir overflow elevation - 1212
Lower sluice gate, centerline elevation - 1189

Beneath Dam:
Type - Steel pipe
Diameter - 42 in
Length - 900 ft
Discharge pipe, elevation (varies) - 1147.5 to 1181

To Mill Creek Return Canal:
Valve type - butterfly valve
Diameter - 42 in
Length - 460 ft
Invert elevation at discharge end - 1210

To Russell Creek Canal:
Pipe Diameter - 36 in
Length - 125 ft
Howell-Bunger valve, elevation - 1147.5

Outlet Canals
Mill Creek Return Canal:
Type - Trapezoidal
Slope - .0008
Lining - Shotcrete
Hydraulic capacity - 190 cfs
Invert elevation at discharge end - 1210 ft

Russell Creek Canal:
Type - Trapezoidal
Slope - 0.01
Lining - Concrete
Hydraulic capacity - 250 cfs
Howell-Bunger valve elevation - 1147.5

Division Works
First Division Works
Mill Creek:
Gate type - Vertical lift gate
Size of opening:
Total width of openings - 97 ft
Height - 6 ft
Channel capacity - 3,500 cfs
Barrier height - 2 ft

To Yellowhawk-Garrison Canal:
Gate type - Radial lift gate
Total width of openings - 14 ft
Height - 6 ft

Fish Ladder
Operating Elevations:
Width - 8
Ladder design capacity - 15 cfs
Slope - 0
Entrance invert elevation - 1170
Exit invert elevation - 1170

Second Division Works
Yellowhawk Creek:
Ungated - 60
Channel capacity - 60 cfs

Garrison Creek:
Gate type - Slide gate
Channel capacity - 10 cfs

Mill Creek Flood Control Zone District Units
Gose Street to Mullan Avenue:
Type - Riprapped levee
Length - 1.9 miles
Capacity - 3,500 cfs

Mullan Avenue to Roosevelt Street:
Type - Concrete-lined
Length - 2.2 miles
Capacity - 5,400 cfs

Roosevelt Street to Diversion Dam:
Type - Riprapped levee
Length - 2.8 miles
Capacity - 3,500 cfs

Hydrologic Data
5-year flood event, natural - 2,000 cfs
5-year flood event, regulated - 1,470 cfs****
100-year flood event, natural - 7,050 cfs
100-year flood event, regulated - 3,500 cfs
Standard project flood - 11,300 cfs
Largest flood, 1931 - 6,000 cfs
Mill Creek drainage basin above Mill Creek at Walla Walla stream gage - 96 sq miles

*Authorizing legislation is Public Law 75-761, as amended by Public Law 77-228.
**These figures represent data from the Walla Walla District's Geographic Information System. Legal real estate documents may vary slightly.
***For the purpose of consistency with existing Mill Creek Project documents, the use of the terms "pool," "reservoir," or &qout;lake" is interchangeable.

The body of water currently known as Virgil B. Bennington Lake has, in the past, also been referred to as "pool," "Mill Creek Reservoir," and "Mill Creek Lake."

****1,400 cfs in Mill Creek and 70 cfs in Yellowhawk and Garrison Creeks.

Contact Us

Mill Creek Office
3211 Reservoir Road
Walla Walla, WA 99362-8400
Phone: 509-527-7160