Granite Diversion Reservoir Report
Last Updated: December 19, 2025
Granite Diversion, located in the picturesque Ketchikan Gateway, Alaska, is a gravity dam completed in 1957 for hydroelectric and water supply purposes.
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Summary
With a height of 14 feet and a length of 50 feet, this dam holds a storage capacity of 456 acre-feet, providing a vital water resource for the region. The dam, built on rock foundations, is regulated by the Federal Energy Regulatory Commission and inspected by the same agency to ensure its safety and compliance with regulations.
Despite its low hazard potential, Granite Diversion poses a high risk due to its age and lack of condition assessment data. With a spillway width of 18 feet and three slide gates for outlet control, the dam plays a crucial role in managing water resources in the area. While the dam has not undergone recent modifications, its emergency action plan was last revised in June 2020, highlighting the importance of preparedness for any potential risks or emergencies that may arise.
For water resource and climate enthusiasts, Granite Diversion serves as a fascinating example of sustainable hydroelectric infrastructure in a remote Alaskan setting. Its location on Granite Creek, with a drainage area of 2.3 square miles, underscores the crucial role it plays in harnessing water for both energy production and supply. As efforts to mitigate climate change intensify, dams like Granite Diversion will continue to be essential in managing water resources and supporting sustainable development in the region.
Year Completed |
1957 |
Dam Length |
50 |
Dam Height |
14 |
River Or Stream |
Granite Creek |
Primary Dam Type |
Gravity |
Surface Area |
1 |
Drainage Area |
2.3 |
Nid Storage |
456 |
Outlet Gates |
Slide (sluice gate) - 3 |
Hazard Potential |
Low |
Foundations |
Rock |
Nid Height |
14 |
Seasonal Comparison
Weather Forecast
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Granite Diversion