Lower Silvis is a rockfill dam located in Ketchikan Gateway Borough, Alaska, built in 1954. It carries a Low hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 32 ft32 ft tall and 140 ft long, taller than 74% of U.S. dams with a recorded height. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic rockfill embankment section and the water level is illustrative.
About Lower Silvis
The primary purpose of Lower Silvis 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 City of Ketchikan (local government). It impounds the Beaver Falls Creek, George Inl.
The dam stands 32 feet tall and stretches 140 feet across, creates a reservoir covering 68 acres, has a maximum storage capacity of 1,600 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1954, the structure is well into its service life at over 50 years old.
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 08/07/2019.
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Location
| State | Alaska |
| County | Ketchikan Gateway Borough |
| Nearest City | None |
| River/Stream | Beaver Falls Creek, George Inl |
| Coordinates | 55.38245, -131.50098 |
Physical Characteristics
| Dam Type | Rockfill |
| NID Height | 32 ft |
| Dam Height | 32 ft |
| Dam Length | 140 ft |
| Year Completed | 1954 (72 years old) |
Storage & Hydraulics
| NID Storage | 1,600 acre-ft |
| Max Storage | 1,600 acre-ft |
| Normal Storage | 1,400 acre-ft |
| Surface Area | 68 acres |
| Drainage Area | 1 sq mi |
| Max Discharge | 7,900 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner | City of Ketchikan |
| Owner Type | Local Government |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 08/07/2019 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | AK00008 |
| Federal ID | AK00008 |
| More Info | State Dam Safety Program |