Little Thompson Reservoir Report

Last Updated: December 5, 2025

Little Thompson, also known as Hillsboro, is a private earth dam located in Weld County, Colorado, specifically in the city of Milliken.


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Summary

Completed in 1896, this irrigation dam stands at 29 feet tall and stretches 1000 feet in length, with a storage capacity of 767 acre-feet. It is regulated by the Colorado Department of Water Resources and undergoes regular inspections to ensure its structural integrity.

The dam's primary purpose is irrigation, serving the local community by providing water for agricultural use. It is situated on the Little Thompson River-OS and is managed by private owners. Despite its significant hazard potential, the dam is currently in satisfactory condition and meets regulatory guidelines. With a moderate risk assessment rating, the dam is equipped with an uncontrolled spillway and has a maximum discharge capacity of 618 cubic feet per second.

Water resource and climate enthusiasts will find Little Thompson to be a historic and essential infrastructure in Colorado's water management system. Its presence contributes to the region's agricultural sustainability and highlights the importance of proper dam maintenance and regulation in the face of changing climate conditions. As a key player in local water resource management, Little Thompson stands as a testament to the ongoing efforts to balance water usage, safety, and environmental stewardship in the region.

Year Completed

1896

Dam Length

1000

Dam Height

29

River Or Stream

LITTLE THOMPSON RIVER-OS

Primary Dam Type

Earth

Surface Area

30

Hydraulic Height

29

Nid Storage

767

Structural Height

29

Hazard Potential

Significant

Nid Height

29
       
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.