Williams-Sherman Reservoir Reservoir Report

Last Updated: December 13, 2025

Williams-Sherman Reservoir, also known as Upper Twelvemile Reservoir, is a privately owned water resource located in Harney, Oregon.


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Summary

Constructed in 1919, this earth dam reservoir serves primarily for irrigation purposes along the North Fork 12 Mile Creek. With a capacity of 300 acre-feet and a surface area of 22 acres, the reservoir plays a crucial role in supporting agricultural activities in the region.

Despite its low hazard potential, the reservoir is regulated by the Oregon Water Resources Department, ensuring its proper inspection, maintenance, and enforcement of regulations. The dam stands at 25 feet high and has a hydraulic height of 11 feet, with a maximum discharge of 665.5 cubic feet per second. In case of emergencies, the reservoir has an uncontrolled spillway, although specific emergency action plans and risk management measures are yet to be fully documented.

Overall, Williams-Sherman Reservoir is a vital water resource in the region, contributing to the irrigation needs of the area. Its moderate risk rating indicates the importance of regular inspections and adherence to safety guidelines to ensure the continued functionality and safety of the dam. As water resource and climate enthusiasts, this reservoir presents an intriguing case study in balancing water management for agricultural purposes while mitigating potential risks associated with dam infrastructure.

Year Completed

1919

Dam Length

600

Dam Height

25

River Or Stream

NORTH FORK 12 MILE CREEK

Primary Dam Type

Earth

Surface Area

22

Hydraulic Height

11

Drainage Area

9.1

Nid Storage

300

Structural Height

25

Hazard Potential

Low

Nid Height

25
       
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.