Chessman Main Dam Reservoir Report

Last Updated: December 5, 2025

Chessman Main Dam, located in Rimini, Montana, is a vital water supply structure owned by the local government and regulated by the Montana Department of Natural Resources and Conservation.


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Summary

Built in 1908, this earth dam stands at a height of 57 feet and stretches 440 feet in length, with a storage capacity of 2370 acre-feet on Beaver Creek. The dam serves the primary purpose of water supply, with a normal storage capacity of 1630 acre-feet and a maximum discharge of 30 cubic feet per second.

With a high hazard potential and satisfactory condition assessment, Chessman Main Dam underwent its last inspection in August 2020, emphasizing the importance of consistent monitoring and maintenance for public safety. The dam features a controlled spillway with a width of 105 feet, ensuring effective water management during peak flow periods. Despite its age, the dam remains structurally sound and meets regulatory requirements, showcasing the resilience of this multi-arch design in soil foundation.

In the midst of increasing climate variability, Chessman Main Dam stands as a crucial infrastructure for water resource management in Lewis and Clark County. Its location in a high-risk area highlights the need for proactive risk management measures to mitigate potential hazards and ensure the continued safe operation of this essential water supply structure.

Year Completed

1908

Dam Length

440

Dam Height

57

River Or Stream

BEAVER CREEK

Primary Dam Type

Earth

Surface Area

114

Hydraulic Height

40

Drainage Area

1.33

Nid Storage

2370

Structural Height

57

Hazard Potential

High

Foundations

Soil

Nid Height

57
       
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.