Cook Reservoir (Wash) Reservoir Report
Nearby: Hochstein Dam #3 Pierson-Upper
Last Updated: December 13, 2025
Cook Reservoir, also known as Hochstein Upper, is a private water storage facility located in Oregon, specifically in Washington County.
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Summary
Managed by a private owner, this reservoir serves primarily for irrigation purposes, storing up to 14 acre-feet of water with a normal storage capacity of 13.6 acre-feet. Built in 1972, the earth dam stands at a height of 27.5 feet and spans 160 feet in length, with a hydraulic height of 22 feet.
Situated along the Tualatin River tributary, Cook Reservoir plays a crucial role in water resource management in the region, covering a surface area of 2.7 acres and having a maximum discharge capacity of 72.9 cubic feet per second. Despite its significant hazard potential, the dam has not been rated for its current condition. With a controlled outlet featuring Needle gates, the facility undergoes regular inspections every three years to ensure its structural integrity and compliance with state regulations. Although located near individual residences, the reservoir remains a key asset for agricultural water supply in the area.
Overall, Cook Reservoir serves as a vital component of the local water infrastructure, contributing to irrigation needs and water resource management in Washington County, Oregon. With its strategic location, substantial storage capacity, and essential role in supporting agricultural activities, the reservoir underscores the importance of sustainable water management practices in the face of changing climate conditions. As a state-regulated facility subject to inspection and enforcement by the Oregon Water Resources Department, Cook Reservoir remains a key player in ensuring water security and resilience in the region.
Year Completed |
1972 |
Dam Length |
160 |
Dam Height |
27.5 |
River Or Stream |
TUALATIN RIVER, TRIB TO |
Primary Dam Type |
Earth |
Surface Area |
2.7 |
Hydraulic Height |
22 |
Drainage Area |
0.51 |
Nid Storage |
14 |
Structural Height |
27.5 |
Outlet Gates |
Needle |
Hazard Potential |
Significant |
Nid Height |
28 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Tualatin River Near Dilley
|
1130cfs |
Willamette River At Newberg
|
52600cfs |
Fanno Creek At Durham
|
36cfs |
East Fork Dairy Creek Near Meacham Corner
|
21cfs |
Fanno Creek At 56th Ave
|
3cfs |
South Yamhill River At Mcminnville
|
8310cfs |
Dam Data Reference
Condition Assessment
SatisfactoryNo existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.
Hazard Potential Classification
HighDams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.
Cook Reservoir (Wash)