Wasco Dam

Overview

Wasco Dam is a 59-foot-high zoned earthfill structure that contains 57,000 cubic yards of material. The crest is 20 feet wide and 415 feet long. The reservoir behind the dam has a total capacity of 13,100 acre-feet (active 11,900 acre-feet) and a surface area of 557 acres. The outlet works consists of 20-foot-wide approach and outlet channels, a submerged vertical intake structure, a single rectangular 4- by 5-foot conduit, a gate chamber with two 3-foot-square slide gates and two overflow weirs, and a 56-foot-long stilling basin. The slide gates are operated manually by two lifts on top of the gate chamber structure at the crest of the dam. The emergency spillway, crossing the left abutment, consists of an unlined channel with a base width of 30 feet. A concrete overflow grade wall is in the spillway 10 feet upstream of the axis of the dam.

In October 1997, a restriction limiting reservoir operation to elevation 3505.0 feet was imposed due to seepage on the face of the dam which occurs above this elevation. This 9-foot restriction reduces the available reservoir capacity to 7,000 acre-feet.

Geology

Wasco Dam is in a narrow valley with steep slide slopes.  The left abutment juts out into the valley and at a height of 50 feet above the stream flattens off into a bench.  Ice or glacial deposits, causing ice or glacial melt water to discharge once blocked the stream channel over a bench a few hundred feet behind the left abutment.  A channel developed which extends from this rock bench to a point in the present channel a few hundred feet downstream from the dam site.  Bedrock at the lowest point of the old channel is about 15 feet above the reservoir flow line.  Overburden at the flow line on the right abutment consisted of 28 feet of gravel with excess sand and silt.  Boulders were hard, fresh andesite 2 to 3 feet in diameter.  Much of the over burden between flow line and the valley flow was undoubtedly quite permeable.


General
RegionFacilities in Pacific Northwest | Pacific Northwest Home Page
StateOregon
CountyWasco
ProjectWapinitia
Dam TypeZoned Earthfill
ReservoirClear Lake
WatercourseClear Creek
Location
Longitude-121.6895197
Latitude45.1748403
Original Construction1958-1959
Modified Construction
National ID NumberOR00326
Hydrologic Unit Code

Dimensions
Structural Height59.0 ft
Hydraulic Height (Normal Operating Depth at Dam)40.0 ft
Top Parapet (Elevation)
Spillway Crest Elevation3520.0 ft
Crest Elevation3526.0 ft
Crest Length415.00 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis3479.90 ft
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation)3514.4 ft
Top of Inactive Conservation Pool (Elevation)3488.00 ft
Top of Dead Storage Pool (Elevation)3479.90 ft

Hydraulics & Hydrology
Total Water Storage at Elevation 11,860 ac-ft
Maximum Water Surface Elevation
Normal Water Surface Elevation3514.4 ft
Spillway Type Outlet overflow weir
Auxiliary SpillwayYes
Spillway Capacity at Elevation170 cfs at 3520.0 ft
Auxiliary Spillway Capacity at Elevation450 cfs at 3526.0 ft
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation230 cfs
Diversion Capacity at Elevation
Drainage Area8.80 sq mi
Hydrometeorological Report (HMR)HMR 57
Probable Maximum Flood (PMF) Report

Contact Information
Owner
TitleArea Office Manager
OrganizationColumbia-Cascades Area Office
Address1917 Marsh Road
CityYakima, WA 98901-2058
Phone (Fax)509 454-5611
Phone (Office)509 575-5848 x202
Operator
OrganizationJuniper Flat District Improvement Company
Address53333 Reservation Road
CityMaupin, OR 97037-9708
Phone (Office)541 328-6380


Last updated: Jun 21, 2012