Lewis Reservoir Report

Last Updated: December 5, 2025

Lewis is a privately owned earth dam located in Big Horn, Wyoming, along Gypsum Creek offstream.


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Summary

Built in 1948 for irrigation purposes, the dam stands at 19 feet high and spans 1540 feet in length. With a storage capacity of 122 acre-feet, Lewis has a spillway width of 40 feet and an uncontrolled spillway type.

Despite its low hazard potential, Lewis is currently in poor condition as of the last inspection in May 2017. The dam is regulated by the Wyoming State Engineer's Office and undergoes regular inspections, with an inspection frequency of 5 years. While the risk assessment for Lewis indicates a moderate level of risk, there are no specific risk management measures or emergency action plans in place.

As a vital water resource structure in the region, Lewis serves as a reminder of the importance of maintaining and monitoring dams for the safety of surrounding communities and the sustainability of water resources in the face of changing climate conditions.

Year Completed

1948

Dam Length

1540

Dam Height

19

River Or Stream

GYPSUM CREEK OFFSTREAM

Primary Dam Type

Earth

Surface Area

19

Hydraulic Height

15

Nid Storage

122

Structural Height

19

Outlet Gates

Valve - 1

Hazard Potential

Low

Foundations

Soil

Nid Height

19
       
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.