Rossmoor Retarding Basin
Rossmoor Retarding Basin is an earth dam located in Orange County, California, built in 2002. It carries a Low hazard potential classification and has a satisfactory condition assessment.
About Rossmoor Retarding Basin
The primary purpose of Rossmoor Retarding Basin is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by County Of Orange (local government). It impounds the Los Alamitos Channel.
The dam stands 14 feet tall and stretches 95 feet across, creates a reservoir covering 25 acres, has a maximum storage capacity of 175 acre-feet, and collects water from a drainage area of 2 square miles. Completed in 2002, the structure is relatively new.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. The most recent inspection on record was 09/17/2025.
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Location
| State | California |
| County | Orange |
| River/Stream | Los Alamitos Channel |
| Coordinates | 33.78770, -118.09140 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 14 ft |
| Dam Height | 14 ft |
| Dam Length | 95 ft |
| Year Completed | 2002 (24 years old) |
Storage & Hydraulics
| NID Storage | 175 acre-ft |
| Max Storage | 175 acre-ft |
| Surface Area | 25 acres |
| Drainage Area | 2 sq mi |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | County of Orange |
| Owner Type | Local Government |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 09/17/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | CA01443 |
| Federal ID | CA01443 |
| More Info | State Dam Safety Program |