Flatiron Reservoir Report

Last Updated: December 5, 2025

Flatiron, also known as Afterbay, is a federal-owned dam located in Larimer County, Colorado.


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Summary

Constructed in 1953 by the Bureau of Reclamation, this earth dam stands at a height of 86 feet, with a primary purpose of hydroelectric generation and irrigation. With a storage capacity of 1,136 acre-feet, Flatiron serves as a crucial water resource for the region.

Situated on Dry Creek-Tr and Chimney Hollow Creek, Flatiron plays a key role in managing water flow and storage in the area. The dam has a surface area of 381,500 square feet and drains an area of 7.42 square miles. Despite its high hazard potential, with a risk assessment rating of 2, Flatiron is regulated and inspected by the Bureau of Reclamation to ensure its structural integrity and safety.

For water resource and climate enthusiasts, Flatiron represents a significant infrastructure for water management in Colorado. With its hydroelectric capabilities and role in irrigation, this dam serves as a vital component of the region's water supply system. As a federally-owned and regulated structure, Flatiron plays a crucial role in safeguarding the surrounding communities from water-related risks and emergencies.

Year Completed

1953

Dam Length

1725

Dam Height

86

River Or Stream

DRY CREEK-TR, CHIMNEY HOLLOW CREEK

Primary Dam Type

Earth

Surface Area

381500

Hydraulic Height

63

Drainage Area

7.42

Nid Storage

1136

Structural Height

86

Hazard Potential

High

Nid Height

86
       
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.