Margaret-Carpenter Reservoir Report

Last Updated: December 5, 2025

Margaret-Carpenter is a locally owned dam located in Thornton, Colorado, along the Grange Hall Creek.


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Summary

Built in 2008, this earth dam stands at a height of 20 feet and serves primarily for irrigation purposes, with additional benefits for recreation. With a storage capacity of 105 acre-feet, the dam covers a surface area of 10 acres and has a drainage area of 1 square mile. The spillway, which is uncontrolled, has a width of 102 feet, allowing for a maximum discharge of 1986 cubic feet per second.

Managed by the local government, Margaret-Carpenter has been regulated and permitted by the Colorado Department of Water Resources. Despite its low hazard potential, the dam undergoes regular inspections every six years, with the latest assessment in April 2019 deeming its condition as satisfactory. With a moderate risk assessment rating of 3, the dam's risk management measures and emergency action plan are yet to be fully documented and updated. Overall, Margaret-Carpenter serves as a vital water resource for the community while adhering to strict regulatory guidelines to ensure public safety and environmental sustainability.

Year Completed

2008

Dam Length

1118

Dam Height

20

River Or Stream

GRANGE HALL CREEK

Primary Dam Type

Earth

Surface Area

10

Hydraulic Height

15

Drainage Area

1

Nid Storage

105

Structural Height

20

Hazard Potential

Low

Foundations

Rock, Soil

Nid Height

20
       
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.