Orville Reservoir Report

Last Updated: December 5, 2025

Orville, also known as Lake Orville, is a privately owned dam located in Angwin, California.


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Summary

Built in 1959, this earth dam stands at a height of 28 feet and serves primarily for water supply purposes, with irrigation and recreation also being supported. The dam has a storage capacity of 89 acre-feet and is situated on Angwin Creek in Napa County.

Managed by the California Department of Water Resources (DWR), the Orville dam is regulated, permitted, inspected, and enforced by state agencies to ensure its safety and functionality. Despite being rated with a high hazard potential, the dam's condition assessment deemed it as satisfactory during the last evaluation in September 2017. The dam's emergency action plan status, risk assessment, and inundation maps are not publicly disclosed, indicating a need for further information on its emergency preparedness.

With its strategic location and critical role in water supply, Orville dam presents both opportunities and challenges for water resource and climate enthusiasts. As a key infrastructure in the region, monitoring its maintenance and safety protocols is crucial to prevent potential hazards and ensure the continuous availability of water for various purposes in the community.

Year Completed

1959

Dam Length

725

Dam Height

28

River Or Stream

Angwin Creek

Primary Dam Type

Earth

Surface Area

10

Hydraulic Height

24.5

Drainage Area

0.69

Nid Storage

89

Hazard Potential

High

Nid Height

28
       
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.