Upper Salmon Falls B-Plant Forebay Reservoir Report
Last Updated: December 16, 2025
Upper Salmon Falls B-Plant Forebay, also known as Upper Powerhouse Forebay Dam, is a private hydroelectric structure located in Twin Falls, Idaho along the Snake River.
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Summary
Built in 1947 by EBASCO, this concrete gravity dam stands at a height of 70 feet and has a storage capacity of 90 acre-feet. With a low hazard potential, the dam features a controlled spillway with a width of 45 feet and two slide (sluice gate) outlet gates.
Operated by the Federal Energy Regulatory Commission, Upper Salmon Falls B-Plant Forebay plays a crucial role in generating hydroelectric power in the region. Its maximum discharge capacity reaches 6500 cubic feet per second, serving as a key component in the local water resource and climate control infrastructure. Although its condition assessment is not currently available, the dam's risk assessment indicates a very high level of risk, highlighting the importance of ongoing monitoring and management measures to ensure its continued safety and functionality.
Year Completed |
1947 |
Dam Length |
318 |
Dam Height |
70 |
River Or Stream |
Snake River |
Primary Dam Type |
Concrete |
Surface Area |
5 |
Hydraulic Height |
69 |
Drainage Area |
32200 |
Nid Storage |
90 |
Structural Height |
73 |
Outlet Gates |
Slide (sluice gate) - 2 |
Hazard Potential |
Low |
Nid Height |
73 |
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.
Upper Salmon Falls B-Plant Forebay
Snake River
Box Canyon