Whittier Narrows Dam Reservoir Report

Last Updated: December 4, 2025

Whittier Narrows Dam, located in Los Angeles, California, serves as a crucial flood risk reduction structure along the San Gabriel River.


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Summary

Built in 1957 by the US Army Corps of Engineers, this earth dam stands at 56 feet tall and has a storage capacity of 66,702 acre-feet. Despite its vital role in managing excess rainfall runoff and preventing downstream flooding, a safety study conducted in 2019 classified the dam's risk as extremely high, particularly during rare, intense rainfall events. In the event of a dam failure, significant downstream flooding could occur, impacting major roadways, highways, and communities, posing a threat to millions of people and billions of dollars in property damage.

To address the high-risk potential of Whittier Narrows Dam, the US Army Corps of Engineers has implemented various risk management measures. These include regular inspections, monitoring instrumentation, emergency action planning, and collaboration with local emergency managers for swift response in case of a crisis. The agency is also working on long-term solutions to address identified concerns and reduce risk as low as possible. Through continuous maintenance, repairs, and monitoring efforts, the USACE aims to ensure the dam's structural integrity while safeguarding surrounding communities from potential disasters.

Water resource and climate enthusiasts keen on understanding the intricate balance between flood risk reduction, water storage, and dam safety will find Whittier Narrows Dam a compelling case study. The complex interplay of extreme weather events, reservoir capacity, and risk mitigation strategies at this iconic structure highlights the critical need for proactive and adaptive approaches to managing water resources in the face of climate change and increasing urbanization.

Year Completed

1957

Dam Length

16960

Dam Height

56

River Or Stream

SAN GABRIEL RIVER

Primary Dam Type

Earth

Surface Area

1

Hydraulic Height

56

Drainage Area

554

Nid Storage

66702

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.
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