Conconully Dam

Overview

Conconully Dam is a hydraulic earthfill structure that when completed in 1910 was 70 feet high, and contained 359,000 cubic yards of fill. In 1920, the dam was raised 2.5 feet. Total capacity of the reservoir is 13,000 acre-feet (active 13,000 acre-feet). During 1968-69, the crest of the dam was repaired with new embankment materials and riprap. The old open-chute concrete spillway that had an inadequate capacity of 6,000 cubic feet per second was replaced with a concrete-baffled apron spillway that has a capacity of 11,580 cubic feet per second.

Geology

Conconully is located in Okanogan Highlands a mountainous district bordered by the Columbia Plateau to the south and the Cascade Mountains to the west, and includes the Colville Mountains which apparently represent a continuation of the higher mountains in British Columbia. The damsite is located in the southern end of the glaciated valley. The effect of the glacial ice was to scour out a depression below the surrounding area much like an enclosed valley. Granite rock generally forms the right wall of the valley; however, at the damsite elevation there exists a short ridge of metamorphic sedimentary rock.  The left abutment and left valley wall are formed in metamorphic sedimentary rock. The valley floor is composed of deposited glacial and alluvial materials such as silt, clay, sand and gravel, as well as boulders and blocks of rock. The spillway is located in the rock ridge of the right abutment. The outlet works was excavated through the metamorphic sedimentary rock comprising the left abutment. The rock is gneiss; light to medium gray on a fresh surface it weathers and oxidizes to a grayish brown. The rock is hard where unweathered and moderately jointed.


General
RegionFacilities in Pacific Northwest | Pacific Northwest Home Page
StateWashington
CountyOkanogan
ProjectOkanogan
Dam TypeHydraulic Earthfill
ReservoirConconully Reservoir
WatercourseSalmon Creek
Location
Longitude-119.7486774
Latitude48.5370932
Original Construction1910-1911
Modified Construction1968-1969
National ID NumberWA00259
Hydrologic Unit Code

Dimensions
Structural Height72.0 ft
Hydraulic Height (Normal Operating Depth at Dam)55.0 ft
Top Parapet (Elevation)
Spillway Crest Elevation2295.3 ft
Crest Elevation2301.0 ft
Crest Length1075.0 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis2232.0 ft
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation)2287.0 ft
Top of Inactive Conservation Pool (Elevation)
Top of Dead Storage Pool (Elevation)2232.4 ft

Hydraulics & Hydrology
Total Water Storage at Elevation13,000 ac-ft
Maximum Water Surface Elevation
Normal Water Surface Elevation2287.0 ft
Spillway TypeUngated overflow w/ baffled chute
Auxiliary SpillwayNo
Spillway Capacity at Elevation11,580 cfs at 2295.3 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation724 cfs at 2287.0 ft
Diversion Capacity at Elevation
Drainage Area121.0 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
OrganizationOkanogan Irrigation District
Address37 A Douglas Road
CityOkanagan, WA 98840
Phone (Office)509 826-1250


Last updated: Jun 21, 2012