Upper Stillwater Reservoir Report

Last Updated: December 4, 2025

Upper Stillwater is a federal-owned concrete gravity dam located in Duchesne, Utah, along the Rock Creek river.


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Summary

Completed in 1986 by the Bureau of Reclamation, this structure serves primarily for irrigation purposes, but also supports recreation and water supply needs in the area. With a maximum storage capacity of 35,253 acre-feet and a normal storage of 33,123 acre-feet, Upper Stillwater plays a crucial role in managing water resources in the region.

Standing at a height of 285 feet and a length of 2,660 feet, Upper Stillwater dam has a spillway width of 600 feet for uncontrolled discharge during high water events. Despite its high hazard potential, the condition assessment of the dam is currently not available, and its last inspection was conducted in August 2020. While the risk assessment is moderate, the emergency action plan for the dam was last revised in June 2020, indicating a commitment to preparedness and safety measures in case of emergencies. For water resource and climate enthusiasts, Upper Stillwater represents a key infrastructure contributing to the sustainability and resilience of water management in the region.

Year Completed

1986

Dam Length

2660

Dam Height

285

River Or Stream

ROCK CREEK

Primary Dam Type

Concrete

Surface Area

329

Hydraulic Height

198

Drainage Area

102

Nid Storage

35253

Structural Height

285

Hazard Potential

High

Foundations

Rock

Nid Height

285
       
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.