Dry Poison Irrigation Reservoir Report

Last Updated: December 13, 2025

Dry Poison Irrigation, located in Johnson County, Wyoming, is a privately owned earth dam built in 1970 for the primary purpose of irrigation along the Murphy Draw river system.


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Summary

With a structural height of 36 feet and a capacity of 122 acre-feet, the dam services a surface area of 5 acres and has a spillway width of 10 feet. Despite its low hazard potential, the dam's condition assessment is deemed poor, highlighting the need for regular inspections and maintenance to ensure its structural integrity.

The irrigation dam is under state regulation and jurisdiction, with permitting, inspection, and enforcement carried out by the Wyoming State Engineer's Office. The last inspection in July 2019 revealed a moderate risk level, prompting the need for risk management measures to mitigate potential hazards. While the dam's hazard potential is low, its poor condition assessment underscores the importance of proactive maintenance to prevent any unforeseen emergencies that could impact the surrounding area.

As a crucial component of water resource management in the region, Dry Poison Irrigation plays a vital role in supporting agricultural activities in Arvada, Wyoming. With its close proximity to the Murphy Draw river system, the dam serves as a key infrastructure for water storage and distribution, highlighting the need for continued monitoring and maintenance to ensure the long-term sustainability of water resources in the area.

Year Completed

1970

Dam Length

415

Dam Height

32

River Or Stream

MURPHY DRAW

Primary Dam Type

Earth

Surface Area

5

Hydraulic Height

26

Nid Storage

122

Structural Height

36

Outlet Gates

Uncontrolled - 0

Hazard Potential

Low

Foundations

Soil

Nid Height

36
       
Seasonal Comparison

Weather Forecast

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.