Magnuson #1 Reservoir Report

Last Updated: December 5, 2025

Magnuson #1, also known as Lake Magnuson, is a privately-owned Earth-type dam located in Florissant, Colorado.


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Summary

Built in 1969 by the USDA NRCS, this dam serves primarily for recreation purposes, with a height of 32 feet and a length of 333 feet. Despite its low hazard potential, the dam has a moderate risk assessment rating of 3, indicating the need for continued monitoring and risk management measures.

Situated on Grape Creek in Teller County, Magnuson #1 has a maximum storage capacity of 88 acre-feet and a normal storage level of 58 acre-feet. The dam's spillway is uncontrolled with a width of 37 feet, allowing for a maximum discharge of 938 cubic feet per second. While the condition assessment in December 2020 deemed the dam to be in satisfactory condition, its risk assessment underscores the importance of ongoing inspections and preparedness measures to mitigate any potential risks associated with its operation.

With the oversight of the Colorado Department of Water Resources, Magnuson #1 stands as a testament to the intricate balance between water resource management and recreational utilization. As water resource and climate enthusiasts continue to advocate for sustainable practices, the importance of maintaining and evaluating dams like Magnuson #1 remains paramount in ensuring the safety and resilience of our water infrastructure in the face of changing environmental conditions.

Year Completed

1969

Dam Length

333

Dam Height

32

River Or Stream

GRAPE CREEK-TR

Primary Dam Type

Earth

Surface Area

6

Hydraulic Height

27

Nid Storage

88

Structural Height

52

Hazard Potential

Low

Nid Height

52
       
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.