Pat Reservoir Report
Nearby: Rattlesnake No. 1 Donaldson
Last Updated: December 5, 2025
Pat is a privately owned Earth dam located in Johnson, Wyoming, along Caple Draw river.
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Summary
Built in 1958 for fire protection, stock, and small fish pond purposes, Pat stands at a height of 36 feet with a hydraulic height of 32 feet. Despite its low hazard potential, the dam is in poor condition and was last inspected in June 2021.
The dam has a storage capacity of 65 acre-feet and a surface area of 9 acres. With an uncontrolled spillway type and a spillway width of 46 feet, Pat poses a moderate risk (3) due to its condition assessment. Although the dam is not regulated by federal agencies, the State of Wyoming oversees its permitting, inspection, and enforcement processes.
Water resource and climate enthusiasts interested in Pat will find its location and historical significance compelling. As one of the many dams contributing to water management in Wyoming, Pat serves as a reminder of the importance of maintaining and monitoring infrastructure in the face of changing environmental conditions.
Year Completed |
1958 |
Dam Length |
220 |
Dam Height |
36 |
River Or Stream |
CAPLE DRAW |
Primary Dam Type |
Earth |
Surface Area |
9 |
Hydraulic Height |
32 |
Nid Storage |
65 |
Structural Height |
36 |
Outlet Gates |
None |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
36 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Piney Creek At Kearny
|
113cfs |
Powder River At Arvada
|
156cfs |
Clear Creek Near Buffalo
|
12cfs |
Rock Creek Near Buffalo
|
70cfs |
Wild Horse Creek Near Arvada
|
0cfs |
South Piney Creek At Willow Park
|
0cfs |
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.
Pat