Main Reservoir Report

Nearby: East Smith

Last Updated: December 5, 2025

Main, also known as Big Osner, is a private water resource located in Jefferson County, Colorado.


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Summary

Built in 1908 for irrigation purposes, this Earth-type dam stands at a height of 45 feet and has a storage capacity of 1320 acre-feet. With a spillway width of 60 feet and a maximum discharge of 700 cubic feet per second, Main plays a crucial role in managing water flow and storage in the region.

The dam is state-regulated by the Colorado Department of Water Resources, ensuring that it is regularly inspected, maintained, and enforced for safety and compliance. Despite its high hazard potential, Main has been assessed as satisfactory in condition, with a moderate risk level of 3. Additionally, the dam has a history of being updated and meeting regulatory guidelines, showcasing a commitment to responsible water management and risk mitigation in the face of changing climate patterns and water resource challenges.

Located in Lakewood, Main serves not only for irrigation but also for recreational purposes, highlighting its multi-functional role in the community. With its historical significance and essential contribution to water supply and management, Main stands as a testament to the importance of sustainable water resource practices in the face of climate variability and increasing water demands.

Year Completed

1908

Dam Length

1081

Dam Height

45

River Or Stream

WEIR GULCH-OS

Primary Dam Type

Earth

Surface Area

39

Hydraulic Height

40

Drainage Area

1

Nid Storage

1320

Structural Height

46

Hazard Potential

High

Nid Height

46
       
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.