Northern Pacific Reservoir Dam Reservoir Report

Last Updated: December 5, 2025

The Northern Pacific Reservoir Dam, located in Jefferson County, Montana, is a privately-owned structure designed for water supply purposes on McClellan Creek.


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Summary

Completed in 1935, this gravity dam stands at a height of 35 feet and has a storage capacity of 173 acre-feet. With a maximum discharge of 800 cubic feet per second, the dam serves as a vital resource for water management in the region.

Despite its age, the Northern Pacific Reservoir Dam is still in operation and regulated by the Montana Department of Natural Resources and Conservation (DNRC). With a high hazard potential, the dam plays a crucial role in maintaining water levels and providing essential water resources to the surrounding area. The dam's condition assessment is currently listed as "Not Rated," indicating a need for further evaluation to ensure its continued safety and effectiveness.

As a key feature in the water infrastructure of East Helena, the Northern Pacific Reservoir Dam serves as a reminder of the importance of proper dam maintenance and regulation in the face of changing climate conditions. With its historic significance and ongoing role in water supply, this gravity dam continues to be a valuable asset in managing water resources in the region.

Year Completed

1935

Dam Length

107

Dam Height

35

River Or Stream

MCCLELLAN CREEK

Primary Dam Type

Gravity

Surface Area

18

Hydraulic Height

35

Drainage Area

33.6

Nid Storage

173

Hazard Potential

High

Foundations

Rock, Soil

Nid Height

35
       
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.