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

Location:
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:

Spillway
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
Headworks:
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)

Canal:
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


References
*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.