Rossmoor Retarding Basin Reservoir Report

Last Updated: December 5, 2025

Located in Rossmoor, California, the Rossmoor Retarding Basin is a crucial piece of infrastructure designed for flood risk reduction along the Los Alamitos Channel.


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Summary

Completed in 2002, this earth dam stands at 14 feet in height and has a storage capacity of 175 acre-feet. With a low hazard potential and a satisfactory condition assessment as of 2017, the basin plays a key role in protecting the surrounding area from potential flooding events.

Managed by local government authorities and regulated by the Department of Water Resources (DWR) and Safety of Dams, the Rossmoor Retarding Basin undergoes regular inspections to ensure its structural integrity and functionality. Situated within the Orange County jurisdiction, this basin serves as a vital component of the region's water resource management strategy. The dam's primary purpose is to mitigate flood risks, highlighting its importance in safeguarding the community against water-related disasters.

With a maximum discharge capacity and a surface area of 25 acres, the Rossmoor Retarding Basin is a significant asset in the area's water infrastructure. As climate change impacts continue to pose challenges to water resources, the effective management and maintenance of structures like this basin are essential in mitigating flood risks and ensuring the safety of residents in Rossmoor and beyond.

Year Completed

2002

Dam Length

95

Dam Height

14

River Or Stream

Los Alamitos Channel

Primary Dam Type

Earth

Surface Area

25

Hydraulic Height

9.8

Drainage Area

2.7

Nid Storage

175

Hazard Potential

Low

Nid Height

14
       
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.