Four Mile Reservoir Report
Nearby: Taylor No. 1 Bruce
Last Updated: December 14, 2025
Four Mile is a privately-owned earth dam located in Johnson, Wyoming, along Four Mile Creek.
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Summary
Built in 1944 for irrigation purposes, this dam stands at 18 feet high with a hydraulic height of 13 feet and a length of 700 feet. It has a storage capacity of 136 acre-feet and a surface area of 12 acres, serving as a vital resource for the surrounding agricultural community.
Despite its low hazard potential, the dam is currently in poor condition, as assessed in 2017. Regular inspections are conducted every 5 years to ensure its safety and functionality. With a spillway width of 200 feet and an uncontrolled spillway type, the dam's risk assessment indicates a moderate level of risk (3) and highlights the need for ongoing risk management measures to address potential concerns.
Located in a beautiful natural setting, Four Mile dam represents a historic piece of infrastructure that requires maintenance and attention to continue serving its irrigation purpose effectively. Water resource and climate enthusiasts can appreciate the importance of preserving and managing such structures to safeguard water supplies and mitigate risks associated with aging infrastructure.
Year Completed |
1944 |
Dam Length |
700 |
Dam Height |
18 |
River Or Stream |
FOUR MILE CREEK |
Primary Dam Type |
Earth |
Surface Area |
12 |
Hydraulic Height |
13 |
Nid Storage |
136 |
Structural Height |
18 |
Outlet Gates |
Valve - 1 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
18 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Four Mile
Powder River (Cantonment Reno)