Duncan Reservoir Report

Last Updated: December 5, 2025

Duncan Reservoir, also known simply as Duncan, is a privately owned water resource located in Modoc County, California, near the city of Canby.


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Summary

Built in 1919, this earth dam stands at a height of 19 feet and has a storage capacity of 2575 acre-feet. The primary purpose of Duncan Reservoir is water supply for irrigation and other uses, drawing from the Tr Pit River.

Managed by the Natural Resources Conservation Service, Duncan Reservoir is regulated by the California Department of Water Resources for safety and compliance. While the dam is considered to have a significant hazard potential, its condition assessment in 2017 was rated as satisfactory. The last inspection in August 2019 showed no immediate concerns, and the dam meets state permitting, inspection, and enforcement standards.

With its rich history dating back over a century, Duncan Reservoir serves as a vital water source in the region, supporting agricultural and community needs. As a notable feature in the San Francisco District, this reservoir showcases the importance of proper dam management and maintenance to ensure the safety and sustainability of water resources amidst changing climate conditions.

Year Completed

1919

Dam Length

900

Dam Height

19

River Or Stream

Tr Pit River

Primary Dam Type

Earth

Surface Area

353

Hydraulic Height

15

Drainage Area

11

Nid Storage

2575

Hazard Potential

Significant

Nid Height

19
       
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.