Union Reservoir Report

Last Updated: December 5, 2025

Union, also known as Calkins Lake, is a privately owned dam located in Weld County, Colorado, near the city of Platteville.


°F

°F

mph

Wind

%

Humidity

Summary

This earth-type dam was completed in 1902 and serves primarily for irrigation purposes, with additional functions including fish and wildlife pond creation and recreational activities. The dam stands at a height of 33 feet and has a storage capacity of 16,250 acre-feet, providing vital water resources for the surrounding area.

Managed by the Colorado Department of Water Resources, Union Dam is subject to state regulations, inspections, and enforcement to ensure its safe operation. With a significant hazard potential and a moderate risk assessment rating, the dam has a satisfactory condition assessment as of August 2019. The spillway, designed as uncontrolled, has a width of 900 feet to accommodate a maximum discharge of 14,925 cubic feet per second, protecting downstream areas in case of overflow.

Despite its age, Union Dam remains a critical infrastructure for water management in the region, showcasing the importance of proper maintenance and regulation to mitigate potential risks and ensure the safety of surrounding communities. With its historical significance and ongoing role in providing essential water resources, Union Dam stands as a testament to the intersection of water management, climate resilience, and environmental stewardship in Colorado.

Year Completed

1902

Dam Length

1200

Dam Height

33

River Or Stream

ST VRAIN CREEK-TR

Primary Dam Type

Earth

Surface Area

717

Hydraulic Height

28

Drainage Area

6

Nid Storage

16250

Structural Height

33

Hazard Potential

Significant

Nid Height

33
       
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.