Tiger Creek Afterbay Reservoir Report

Last Updated: December 5, 2025

Tiger Creek Afterbay, located in Pioneer, California, is a privately owned hydroelectric facility situated on the North Fork Mokelumne River.


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Summary

The dam, completed in 1931, stands at a height of 120 feet and has a storage capacity of 2,610 acre-feet. With a maximum discharge of 194,370 cubic feet per second, the controlled spillway, measuring 292 feet wide, ensures efficient water release during high flow events.

Managed by the Federal Energy Regulatory Commission, Tiger Creek Afterbay has a high hazard potential due to its structural height and proximity to populated areas. The facility boasts 10 radial Tainter gates for water control, ensuring the safety and stability of the dam. Despite its age, the dam's condition assessment is not currently available, highlighting the importance of regular inspections and maintenance to mitigate risks associated with its very high risk rating.

Water resource and climate enthusiasts will be fascinated by Tiger Creek Afterbay's historical significance and vital role in hydroelectric power generation. As a key component of California's water infrastructure, the facility's efficient design and regulated operation showcase the intersection of human ingenuity and environmental stewardship. With a strong emphasis on safety and risk management measures, Tiger Creek Afterbay stands as a testament to the ongoing efforts to balance water resource utilization with conservation and public safety in the face of changing climate conditions.

Year Completed

1931

Dam Length

448

Dam Height

120

River Or Stream

North Fork Mokelumne River

Primary Dam Type

Concrete

Surface Area

70

Hydraulic Height

101.8

Drainage Area

357

Nid Storage

2610

Structural Height

120

Outlet Gates

Tainter (radial) - 10

Hazard Potential

High

Nid Height

120
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.