Nimbus Reservoir Report

Last Updated: December 5, 2025

Nimbus is a federal structure located in Fair Oaks, California, along the American River.


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Summary

Constructed in 1955, this concrete dam stands at a height of 87 feet and serves multiple purposes, including fish and wildlife pond management, hydroelectric power generation, irrigation, and recreation. Managed by the Bureau of Reclamation, Nimbus has a storage capacity of 8,800 acre-feet and covers a surface area of 540 acres.

With a high hazard potential and a very high risk assessment rating, Nimbus plays a crucial role in water resource management and flood control within the Sacramento region. The dam has a controlled spillway with a width of 720 feet and a maximum discharge capacity of 300,000 cubic feet per second. Despite its age, the condition assessment of Nimbus is currently listed as "Not Available", highlighting the need for regular monitoring and maintenance to ensure its continued safety and functionality.

As a key component of the American River watershed, Nimbus is a significant infrastructure asset that supports the local ecosystem, agriculture, and recreational activities. Climate change and increasing water demands necessitate ongoing vigilance and investment in the upkeep of structures like Nimbus to safeguard water resources and mitigate potential risks to surrounding communities.

Year Completed

1955

Dam Length

1093

Dam Height

87

River Or Stream

AMERICAN RIVER

Primary Dam Type

Concrete

Surface Area

540

Hydraulic Height

47

Drainage Area

1898

Nid Storage

8800

Structural Height

87

Hazard Potential

High

Foundations

Rock

Nid Height

87
       
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.