Pershall Reservoir Report

Last Updated: December 13, 2025

Pershall, a privately owned dam located in Owyhee County, Idaho, stands as a critical water resource management structure in the region.


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Summary

Built in 1948, this earth dam primarily serves purposes other than flood control or irrigation, with a storage capacity of 50 acre-feet and a drainage area of 1.4 square miles. The dam, standing at a height of 26.9 feet with a hydraulic height of 22.5 feet, harnesses the flow of Rail Creek and Jordan Creek, contributing to the overall water management system in the area.

Despite being classified with low hazard potential and fair condition assessment, Pershall is subject to state regulation and inspection by the Idaho Department of Water Resources. With uncontrolled spillways and a moderate risk assessment rating, the dam poses a certain level of risk that necessitates ongoing monitoring and management. The last inspection in June 2016 revealed a need for continued vigilance, with an inspection frequency of every 5 years to ensure the safety and integrity of the structure. The dam's presence highlights the importance of maintaining a balance between water resource utilization and environmental sustainability in the face of changing climate patterns.

Year Completed

1948

Dam Length

310

Dam Height

26.9

River Or Stream

RAIL CREEK JORDAN CREEK

Surface Area

7

Hydraulic Height

22.5

Drainage Area

1.4

Nid Storage

50

Hazard Potential

Low

Foundations

Rock, Soil

Nid Height

27
       
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.