Masonry Dam is an arch dam located in King County, Washington, built in 1914. It carries a High hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 230 ft230 ft tall and 980 ft long, taller than 99% of U.S. dams with a recorded height. Height is drawn to scale against the Statue of Liberty, 305 ft ground to torch; the profile is a generic arch section and the water level is illustrative.
About Masonry Dam
The primary purpose of Masonry Dam is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Seattle City Light (public utility). It impounds the Cedar River near Cedar Falls.
The dam stands 230 feet tall and stretches 980 feet across, creates a reservoir covering 280 acres, has a maximum storage capacity of 175,000 acre-feet, and collects water from a drainage area of 81 square miles. Completed in 1914, the structure is over a century 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. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 10/01/2020.
At 230 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 | Cedar Falls |
| River/Stream | Cedar River |
| Coordinates | 47.41221, -121.75258 |
Physical Characteristics
| Dam Type | Arch |
| NID Height | 230 ft |
| Dam Length | 980 ft |
| Year Completed | 1914 (112 years old) |
Storage & Hydraulics
| NID Storage | 175,000 acre-ft |
| Max Storage | 175,000 acre-ft |
| Normal Storage | 90,660 acre-ft |
| Surface Area | 280 acres |
| Drainage Area | 81 sq mi |
| Max Discharge | 74,400 cfs |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner | Seattle City Light |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 10/01/2020 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | WA00255 |
| Federal ID | WA00255 |
| More Info | State Dam Safety Program |