Prospect No. 1 Reservoir Report

Last Updated: December 5, 2025

Prospect No.


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Summary

1 is a historic earth dam located along Little Sandy Creek in Sublette, Wyoming. Built in 1914 for irrigation purposes, this dam stands at a height of 20 feet and has a storage capacity of 957 acre-feet. Despite its age, the dam has a low hazard potential and is currently in poor condition, as assessed during its last inspection in 2017. Despite its condition, the dam continues to serve its primary purpose efficiently, while also providing fire protection, stock watering, and small fish pond support to the local area.

The dam's spillway type is uncontrolled, with a width of 10 feet, and it has an outlet gate in the form of a slide (sluice gate). The maximum discharge capacity of the dam is 390 cubic feet per second, ensuring effective water management during peak flow periods. While the dam's risk assessment is moderate, with a rating of 3, there is a need for ongoing maintenance and potential rehabilitation to ensure its long-term stability and safety. Overall, Prospect No. 1 remains a vital water resource infrastructure in Sublette County, Wyoming, contributing to the region's agricultural and ecological sustainability.

Year Completed

1914

Dam Length

838

Dam Height

20

River Or Stream

LITTLE SANDY CREEK

Primary Dam Type

Earth

Surface Area

45

Hydraulic Height

14

Nid Storage

957

Structural Height

19

Outlet Gates

Slide (sluice gate) - 1

Hazard Potential

Low

Foundations

Soil

Nid Height

20
       
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.