Grant Dam Reservoir Report

Last Updated: December 6, 2025

Grant Dam, located in Prairie, Montana, is a gravity dam with a structural height of 19 feet and a hydraulic height of 12 feet.


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Summary

Managed by the Bureau of Land Management, this federal structure on an unnamed drainage system has a storage capacity of 55.8 acre-feet and covers a surface area of 15.1 acres. Despite its low hazard potential, the dam has not been rated for its condition, with the last inspection taking place in September 2018.

This dam, constructed with buttress and stone core types, serves various purposes including irrigation, water supply, and flood control. It stands as a testament to engineering ingenuity in harnessing water resources for the benefit of the surrounding community. With its close proximity to nature and the Bureau of Land Management's oversight, Grant Dam is a vital piece of infrastructure that plays a crucial role in managing water resources in the region.

Water resource and climate enthusiasts will appreciate the significance of Grant Dam in maintaining ecological balance and supporting sustainable water management practices. As a federal structure on federal land, it exemplifies the collaborative efforts between government agencies to ensure the safe and efficient utilization of water resources for the benefit of both humans and the environment. Grant Dam stands as a symbol of innovation and stewardship in the face of evolving climate challenges, highlighting the importance of responsible water resource management in a changing world.

Dam Length

351

River Or Stream

UNNAMED DRAINAGE

Primary Dam Type

Gravity

Surface Area

15.1

Hydraulic Height

12

Drainage Area

5.8

Nid Storage

55.8

Structural Height

19

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

19
       
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.