Three Mile Falls Diversion Reservoir Report

Last Updated: December 13, 2025

Three Mile Falls Diversion, also known as T-52, is a federal-owned irrigation structure located in Umatilla, Oregon on the Umatilla River.


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Summary

Built in 1913 by the Bureau of Reclamation, this concrete dam stands at a height of 28 feet and has a hydraulic height of 23 feet. With a storage capacity of 300 acre-feet and a drainage area of 1280 acres, the dam serves primarily for irrigation purposes.

The structure spans 915 feet in length and covers a surface area of 35 acres. Despite its low hazard potential, Three Mile Falls Diversion has not undergone a recent condition assessment, with the last inspection reported in 2002. The dam is managed and regulated by the Bureau of Reclamation, ensuring its safe operation for the surrounding agricultural community.

With its historical significance and vital role in water resource management, Three Mile Falls Diversion continues to be a key asset in the irrigation infrastructure of Oregon. As climate change impacts water availability in the region, the maintenance and regulation of this dam are crucial for sustaining agricultural activities along the Umatilla River.

Year Completed

1913

Dam Length

915

Dam Height

28

River Or Stream

UMATILLA RIVER

Primary Dam Type

Concrete

Surface Area

35

Hydraulic Height

23

Drainage Area

1280

Nid Storage

300

Structural Height

28

Hazard Potential

Low

Foundations

Rock

Nid Height

28
       
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.