Howard A. Hanson Dam
Howard A. Hanson Dam is a rockfill dam located in King County, Washington, built in 1962. It carries a High hazard potential classification.
About Howard A. Hanson Dam
The primary purpose of Howard A. Hanson Dam 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 Usace - Seattle District (federal). It impounds the Green near Auburn.
The dam stands 235 feet tall and stretches 500 feet across, creates a reservoir covering 20,000 acres, has a maximum storage capacity of 136,700 acre-feet, and collects water from a drainage area of 221 square miles. Completed in 1962, the structure is well into its service life at over 50 years old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. An emergency action plan is in place for this dam. The most recent inspection on record was 11/19/2025.
At 235 feet, this dam is taller than 99% of all dams in the United States.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Washington dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Washington |
| County | King |
| Nearest City | Auburn |
| River/Stream | Green |
| Coordinates | 47.27821, -121.78655 |
Physical Characteristics
| Dam Type | Rockfill |
| NID Height | 235 ft |
| Dam Length | 500 ft |
| Year Completed | 1962 (64 years old) |
Storage & Hydraulics
| NID Storage | 136,700 acre-ft |
| Max Storage | 136,700 acre-ft |
| Normal Storage | 26,000 acre-ft |
| Surface Area | 20,000 acres |
| Drainage Area | 221 sq mi |
| Max Discharge | 129,000 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | USACE - Seattle District |
| Owner Type | Federal |
| Hazard Classification | High |
| Condition Assessment | Not Available |
| Last Inspection | 11/19/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | WA00298 |
| Federal ID | WA00298 |
| More Info | State Dam Safety Program |