Posy No. 1 Reservoir Report
Nearby: Austin No. 1 Will No. 1
Last Updated: December 13, 2025
Posy No.
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Summary
1 is a privately owned earth dam located in Sussex, Wyoming, along Posy Creek. Built in 1995 by designer John Lambert, this dam serves primarily for irrigation purposes, with additional benefits for fire protection, stock, and small fish pond use. Standing at a height of 51 feet, with a hydraulic height of 47 feet, Posy No. 1 has a storage capacity of 2162 acre-feet, making it a crucial water resource for the surrounding area.
Despite its age, Posy No. 1 is deemed to have a low hazard potential and fair condition, as assessed during its last inspection in July 2020. The dam features an uncontrolled spillway with a width of 200 feet and an outlet gate of the slide type. With a drainage area of 15.6 square miles and a maximum discharge of 6650 cubic feet per second, this structure plays a vital role in managing water flow and storage in the region, contributing to water resource sustainability and climate resilience.
Located in Congressional District 00 of Wyoming, Posy No. 1 falls under state jurisdiction and regulation, with permitting, inspection, and enforcement carried out by the State Engineer's Office. With its moderate risk rating and the potential for future modifications or risk management measures, this dam remains a focal point for water resource and climate enthusiasts interested in the intersection of infrastructure, water management, and environmental stewardship.
Year Completed |
1995 |
Dam Length |
1788 |
Dam Height |
51 |
River Or Stream |
POSY CREEK |
Primary Dam Type |
Earth |
Surface Area |
125 |
Hydraulic Height |
47 |
Drainage Area |
15.6 |
Nid Storage |
2162 |
Structural Height |
52 |
Outlet Gates |
Slide (sluice gate) - 1 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
52 |
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.
Posy No. 1
Buffalo Creek (Lower)