Porrini Reservoir Report

Last Updated: December 22, 2025

Porrini is a privately owned irrigation dam located in Lewis and Clark, Montana, along the TR-North Fork Willow Creek.


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Summary

Built in 1952 by the USDA NRCS, this earth dam stands at a height of 10 feet and has a length of 1045 feet, providing a storage capacity of 217 acre-feet for irrigation purposes. The dam is regulated by the Montana Department of Natural Resources and Conservation (DNRC) and is inspected, permitted, and enforced by the state agency.

Despite being classified as having a low hazard potential and not yet rated for its condition assessment, Porrini plays a crucial role in water resource management in the region. The dam is designed to withstand the hydraulic pressure of the North Fork Willow Creek while providing reliable water supply for agricultural activities. As an essential structure in the area, Porrini contributes to the sustainability of water resources and the resilience of the local community in the face of changing climate conditions.

While Porrini has not been fully assessed for its emergency preparedness measures, its presence ensures a steady water supply for irrigation needs in the region. With its strategic location and purpose, the dam showcases the importance of efficient water management practices in the face of climate variability. As water resource and climate enthusiasts, understanding the role of structures like Porrini is vital in ensuring sustainable water use and resilience in the face of a changing climate.

Year Completed

1952

Dam Length

1045

Dam Height

10

River Or Stream

TR-NORTH FORK WILLOW CREEK

Primary Dam Type

Earth

Hydraulic Height

10

Nid Storage

217

Hazard Potential

Low

Nid Height

10
       
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.