Lower Diversion Reservoir Report
Nearby: City Diversion Gem State Left Dike
Last Updated: December 18, 2025
Lower Diversion, located in Shelley, Idaho, is a crucial hydroelectric facility along the Snake River with a primary purpose of generating clean energy.
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Summary
Constructed in 1982, this gravity dam stands at a height of 14 feet and has a storage capacity of 1200 acre-feet, serving as a reliable source of power and recreation for the local community. The dam has a controlled spillway, with a width of 930 feet, to manage water flow and ensure safety during periods of high discharge.
Owned and regulated by the local government and the Federal Energy Regulatory Commission, Lower Diversion undergoes regular inspections to maintain its low hazard potential and ensure its structural integrity. With a drainage area of 9800 square miles and a maximum discharge capacity of 75,000 cubic feet per second, the dam plays a crucial role in managing water resources and mitigating flood risks in the region. Despite its age, Lower Diversion continues to meet safety guidelines and serves as a testament to effective risk management in the face of climate challenges.
Year Completed |
1982 |
Dam Length |
1380 |
Dam Height |
14 |
River Or Stream |
Snake River |
Primary Dam Type |
Gravity |
Surface Area |
100 |
Drainage Area |
9800 |
Nid Storage |
1200 |
Outlet Gates |
Other Controlled - 1, Tainter (radial) - 8 |
Hazard Potential |
Low |
Nid Height |
14 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
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.
Lower Diversion