Sixty Seven Reservoir Report

Last Updated: December 15, 2025

Sixty Seven is a privately owned irrigation dam located in Sublette, Wyoming, specifically in the city of Big Piney.


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Summary

Constructed in 1942 by David P. Miller, this Earth-type dam stands at a height of 32 feet and has a hydraulic height of 27 feet. It serves the primary purpose of irrigation for the surrounding area, with a storage capacity of 7,090 acre-feet and a normal storage level of 6,087 acre-feet. The dam spans 956 feet in length and has a surface area of 371 acres, drawing water from Spring Creek offstream.

Despite its age, Sixty Seven is regulated and inspected by the State of Wyoming, with the State Engineer's Office overseeing its operation, maintenance, and enforcement. The dam has a spillway width of 10 feet and a maximum discharge of 400 cubic feet per second, with one valve serving as its outlet gate. With a high hazard potential and moderate risk assessment, Sixty Seven poses a significant challenge for risk management and emergency preparedness. The dam's last inspection was conducted in August 2020, highlighting the importance of regular monitoring and maintenance to ensure its safety and efficiency in the face of changing climate conditions.

Year Completed

1942

Dam Length

956

Dam Height

32

River Or Stream

SPRING CREEK OFFSTREAM

Primary Dam Type

Earth

Surface Area

371

Hydraulic Height

27

Drainage Area

1.9

Nid Storage

7090

Structural Height

32

Outlet Gates

Valve - 1

Hazard Potential

High

Foundations

Soil

Nid Height

32
       
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.