Pit No. 1 Forebay Reservoir Report

Last Updated: December 5, 2025

Pit No.


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Summary

1 Forebay, located in Fall River Mills, California, is a privately owned hydroelectric dam completed in 1947 with a primary purpose of generating hydroelectric power. The dam stands at 46.5 feet in height with a hydraulic height of 35 feet and a structural height of 44 feet. It has a capacity of storing 3,212 acre-feet of water, with a normal storage level of 614 acre-feet and a maximum discharge of 13,000 cubic feet per second.

The dam spans 586 feet in length and has a surface area of 222 acres, serving a drainage area of 725 acres. It features a controlled spillway with a width of 45 feet and is equipped with two Tainter (radial) outlet gates. The dam's hazard potential is classified as high, and it has a very high risk assessment rating. While the condition assessment of the dam is not available, it is regulated, permitted, inspected, and enforced by various state and federal agencies, including the Federal Energy Regulatory Commission.

Despite its age, Pit No. 1 Forebay remains a crucial component of California's water resource infrastructure, contributing to the generation of clean energy and water management in the region. Its strategic location on the Fall River underscores its importance in the local ecosystem and highlights the need for ongoing monitoring and maintenance to ensure its continued safe operation and resilience in the face of changing climate conditions.

Year Completed

1947

Dam Length

586

Dam Height

46.5

River Or Stream

Fall River

Primary Dam Type

Earth

Surface Area

222

Hydraulic Height

35

Drainage Area

725

Nid Storage

3212

Structural Height

44

Outlet Gates

Tainter (radial) - 2

Hazard Potential

High

Nid Height

47
       
Seasonal Comparison

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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.