Upper Reservoir Report

Last Updated: December 5, 2025

Upper is a privately owned irrigation dam located in Washakie, Wyoming, near the city of Manderson.


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Summary

Built in 1922, this Earth dam stands at a height of 15 feet and has a storage capacity of 373 acre-feet. The dam, designed by C.D. Shawer, is primarily used for irrigation purposes and is regulated by the State Engineer's Office.

Despite being categorized as having a low hazard potential and fair condition assessment, Upper poses a moderate risk due to its location on Spring Branch Brokenback Creek. The spillway, which is uncontrolled and 20 feet wide, is designed to handle any excess water flow. The dam is equipped with two valve outlet gates and undergoes regular inspections every five years to ensure its structural integrity.

In the event of an emergency, the dam does not have an Emergency Action Plan (EAP) in place, raising concerns about its emergency preparedness. However, with its moderate risk level and fair condition assessment, it is crucial for authorities to monitor and address any potential issues to ensure the safety and functionality of Upper for both irrigation and water resource management in the region.

Year Completed

1922

Dam Length

600

Dam Height

15

River Or Stream

SPRING BRANCH BROKENBACK CR

Primary Dam Type

Earth

Surface Area

36

Hydraulic Height

12

Nid Storage

373

Structural Height

15

Outlet Gates

Valve - 2

Hazard Potential

Low

Foundations

Soil

Nid Height

15
       
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.