Koinenia Lake Dam Reservoir Report

Last Updated: December 13, 2025

Koinenia Lake Dam, also known as Lloyd Hill Dam, is a private-owned structure located in Marion County, Oregon.


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Summary

Completed in 1976, this earth-type dam serves primarily for irrigation purposes, with a storage capacity of 125 acre-feet. Situated on the Pudding River, a tributary to the Willamette River, the dam stands at a height of 40 feet and has a hydraulic height of 38 feet.

With a significant hazard potential, Koinenia Lake Dam has not been rated for its current condition. Despite being state-regulated and inspected, the dam's emergency action plan (EAP) status, risk assessment, and inundation maps remain unclear. The dam has a spillway width of 0 feet and a maximum discharge capacity of 188 cubic feet per second, serving a drainage area of 3.1 square miles.

For water resource and climate enthusiasts, the Koinenia Lake Dam represents a vital infrastructure for irrigation in the region, but its maintenance and emergency preparedness require further attention. The dam's location in the picturesque city of Pratum offers a serene backdrop to its essential role in water management and agricultural development. As efforts to assess and mitigate risks associated with the dam continue, stakeholders are urged to monitor its condition and ensure the safety of surrounding communities.

Year Completed

1976

Dam Length

410

Dam Height

40

River Or Stream

PUDDING RIVER, TRIB TO

Primary Dam Type

Earth

Surface Area

4

Hydraulic Height

38

Drainage Area

3.1

Nid Storage

125

Structural Height

42

Hazard Potential

Significant

Nid Height

42
       
Seasonal Comparison

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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.