Hartwick Reservoir Reservoir Report

Last Updated: December 13, 2025

Hartwick Reservoir, located in Orenco, Oregon, is a private water resource managed by the H-20 state agency and regulated by the Oregon Water Resources Department.


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Summary

Built in 1956 for irrigation purposes, this earth dam stands at 30 feet high and spans 540 feet in length, with a storage capacity of 200 acre-feet. The reservoir covers an area of 8.6 acres and is fed by Dairy Creek, a tributary to the Tualatin River.

Despite its low hazard potential and moderate risk assessment, Hartwick Reservoir is equipped with an uncontrolled spillway and has a maximum discharge capacity of 114 cubic feet per second. The dam has not been rated for condition assessment, and its last inspection was conducted in November 2018. With a drainage area of 0.8 square miles, this reservoir plays a critical role in supporting local irrigation needs and sustaining agricultural activities in the region.

As a key component of the water infrastructure in Washington County, Oregon, Hartwick Reservoir serves as a vital resource for water management and agricultural development. Climate and water enthusiasts will appreciate the reservoir's historical significance, engineering design, and its role in ensuring water security for the surrounding community.

Year Completed

1956

Dam Length

540

Dam Height

28

River Or Stream

DAIRY CREEK, TRIB TO

Primary Dam Type

Earth

Surface Area

8.6

Hydraulic Height

24

Drainage Area

0.8

Nid Storage

200

Structural Height

30

Hazard Potential

Low

Nid Height

30
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.