Exchequer Main Reservoir Report

Last Updated: December 5, 2025

Exchequer Main, located in Mariposa, California, is a rockfill dam completed in 1966 with a primary purpose of hydroelectric power generation.


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Summary

It stands at a height of 490 feet and has a storage capacity of 1,100,000 acre-feet, serving multiple purposes including fire protection, irrigation, and recreation. The dam is regulated by the Federal Energy Regulatory Commission and the California Department of Water Resources, ensuring its safety and compliance with state and federal regulations.

The Merced River is the primary source of water for Exchequer Main, with a drainage area of 1,037 square miles and a maximum discharge capacity of 531,600 cubic feet per second. The dam's spillway is controlled with a width of 1,360 feet, and it is equipped with six Tainter gates for water release. Despite being classified as having a high hazard potential, the dam's risk assessment is very high, emphasizing the importance of regular inspections and emergency preparedness. Overall, Exchequer Main plays a critical role in water resource management and climate adaptation efforts in California.

With its strategic location in Snelling and its crucial role in water storage and flood risk reduction, Exchequer Main stands as a vital infrastructure for the region. Its contribution to hydroelectric power generation and its multi-purpose functionality highlight the importance of sustainable water resource management in the face of changing climate conditions. As a key asset in California's water infrastructure, Exchequer Main underscores the need for ongoing monitoring, maintenance, and risk management to ensure the safety and reliability of the dam for future generations.

Year Completed

1966

Dam Length

1220

Dam Height

490

River Or Stream

Merced River

Primary Dam Type

Rockfill

Surface Area

7110

Hydraulic Height

437

Drainage Area

1037

Nid Storage

1100000

Outlet Gates

Tainter (radial) - 6

Hazard Potential

High

Foundations

Unlisted/Unknown

Nid Height

490
       
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.