Milton Main Reservoir Report

Last Updated: December 5, 2025

Milton Main is a significant water resource and climate enthusiast's dream located in Woolsey Flat, California, along the Middle Yuba River.


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Summary

Constructed in 1927, this arch dam stands at 37 feet in height and boasts a storage capacity of 295 acre-feet. Its primary purpose is for water supply, with additional functions including hydroelectric power generation, irrigation, and recreation.

Owned by a public utility and regulated by the Department of Water Resources (DWR) and the Safety of Dams agency in California, Milton Main has a low hazard potential but a moderate risk assessment. The dam features an uncontrolled spillway, with a width of 245 feet, and underwent its last inspection in September 2019. The dam's condition assessment is currently unavailable, but an emergency action plan (EAP) has been prepared and updated periodically.

Overall, Milton Main serves as a vital infrastructure for water management in the region, providing essential services while also offering recreational opportunities. With its historical significance and ongoing maintenance, this dam represents a key component of California's water resource management efforts, showcasing the intersection of engineering, environmental stewardship, and public safety in a changing climate landscape.

Year Completed

1927

Dam Length

286

Dam Height

37

River Or Stream

Middle Yuba River

Primary Dam Type

Arch

Surface Area

810

Hydraulic Height

30.5

Drainage Area

39

Nid Storage

295

Structural Height

35.5

Hazard Potential

Low

Foundations

Rock

Nid Height

37
       
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.