Pioneer Reservoir Report

Last Updated: December 5, 2025

Pioneer, also known as Millken Slough, is a private water structure located in Sweet Grass, Montana.


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Summary

Designed by the USDA NRCS and completed in 1968, this earth dam stands at 25 feet high and spans 200 feet in length. Its primary purpose is classified as "Other," with a low hazard potential and a normal storage capacity of 44 acre-feet.

Situated along the Pioneer Ditch, this water resource is regulated by the state of Montana through the DNRC, with inspection, enforcement, and permitting processes in place. The dam's location in a picturesque setting near Greycliff adds to its appeal for water resource and climate enthusiasts who may be interested in its construction, purpose, and historical significance. Despite not having a current condition assessment, Pioneer remains a notable feature in the local landscape.

With its unique design and historical background, Pioneer serves as a reminder of the importance of water management and conservation efforts in Montana. As a privately owned structure, its presence contributes to the overall water infrastructure of the region, highlighting the collaborative efforts between federal agencies like the Natural Resources Conservation Service and state regulators. For those interested in exploring water resources and climate impacts, Pioneer offers a valuable case study of dam construction and management in a rural setting.

Year Completed

1968

Dam Length

200

Dam Height

25

River Or Stream

PIONEER DITCH

Primary Dam Type

Earth

Hydraulic Height

25

Drainage Area

0.31

Nid Storage

64

Hazard Potential

Low

Nid Height

25
       
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.