Foss Valley Reservoir Report

Last Updated: December 5, 2025

Foss Valley, located in Napa, California, is a privately owned Earth dam completed in 1988 for the primary purpose of water supply.


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Summary

The dam stands at 56 feet tall with a storage capacity of 800 acre-feet and a surface area of 31 acres. It serves multiple purposes including irrigation and recreation, and is regulated by the California Department of Water Resources (DWR) under the Safety of Dams program. The dam is situated on Tr Milliken Creek within the Sacramento District.

With a high hazard potential and satisfactory condition assessment as of September 2017, Foss Valley dam undergoes regular inspections to ensure its safety. The last inspection was conducted in April 2021, highlighting its compliance with state regulations and enforcement. The dam's Emergency Action Plan (EAP) is periodically updated, with the latest review in January 2021, although details on its preparedness and adherence to guidelines are not specified in the data. Despite the lack of specific risk assessments or management measures, Foss Valley remains a vital water resource structure in the region, providing essential services to the surrounding area.

Year Completed

1988

Dam Length

2500

Dam Height

56

River Or Stream

Tr Milliken Cr

Primary Dam Type

Earth

Surface Area

31

Hydraulic Height

52

Nid Storage

800

Hazard Potential

High

Nid Height

56
       
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.