Modesto Reservoir Reservoir Report

Last Updated: December 5, 2025

Modesto Reservoir, located in Modesto, California, is a vital water resource infrastructure primarily used for irrigation and water supply purposes.


°F

°F

mph

Wind

%

Humidity

Summary

Constructed in 1911, this Earth-type dam stands at a height of 36 feet and has a storage capacity of 40,000 acre-feet, serving the needs of the local community and surrounding agricultural areas. The reservoir is situated on the Tuolumne River, covering a surface area of 3,800 acres and draining an area of 10 square miles.

Managed by a public utility agency, Modesto Reservoir is regulated and inspected by the California Department of Water Resources for safety and compliance. Despite its high hazard potential due to its critical role in water supply, the dam's condition assessment in 2017 reported it as satisfactory. With a recent inspection in March 2021 and an emergency action plan prepared, the reservoir is equipped to handle potential risks and emergencies effectively. As a significant water infrastructure in the region, Modesto Reservoir plays a crucial role in ensuring water security and resource sustainability for the local community and beyond.

Year Completed

1911

Dam Length

1235

Dam Height

36

River Or Stream

Tr Tuolumne Rv

Primary Dam Type

Earth

Surface Area

3800

Hydraulic Height

36

Drainage Area

10

Nid Storage

40000

Hazard Potential

High

Nid Height

36
       
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.