Portola Reservoir Report

Last Updated: December 5, 2025

Portola Dam, located in Mission Viejo, California, is a vital part of the region's water supply infrastructure.


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Summary

Completed in 1980, this earth dam stands at a height of 53 feet and has a storage capacity of 586 acre-feet. Its primary purpose is to provide water for irrigation and drinking water needs in the area. The dam is regulated and inspected by the California Department of Water Resources for safety and compliance with state regulations.

The Portola Dam is situated on the Canada Gobernadora River and is managed by a public utility entity. With a high hazard potential, the dam is regularly assessed for its condition and emergency preparedness. The latest inspection in November 2020 found the dam to be in satisfactory condition, meeting safety guidelines. In case of any emergencies, the dam operators have an Emergency Action Plan in place, last revised in December 2020, to ensure swift and effective response.

Enthusiasts of water resources and climate in Orange County can appreciate the significance of the Portola Dam in ensuring a reliable water supply for the community. With its critical role in water storage and distribution, as well as its adherence to regulatory standards and safety measures, the Portola Dam stands as a testament to responsible water management in the region. Its presence on the Canada Gobernadora River contributes to the environmental sustainability and resilience of Mission Viejo and surrounding areas.

Year Completed

1980

Dam Length

1200

Dam Height

53

River Or Stream

Canada Gobernadora

Primary Dam Type

Earth

Surface Area

20

Hydraulic Height

43

Drainage Area

0.18

Nid Storage

586

Hazard Potential

High

Nid Height

53
       
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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.