Big Dalton Reservoir Report

Last Updated: December 5, 2025

Big Dalton Reservoir, located in Glendora, California, is a vital water resource managed by the local government for flood risk reduction and water supply purposes.


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Summary

Built in 1929, this multi-arch dam stands at a height of 153 feet with a storage capacity of 1290 acre-feet. The reservoir's primary source, Big Dalton Wash, serves a drainage area of 4.3 square miles and covers a surface area of 26 acres.

With a high hazard potential but a satisfactory condition assessment as of September 2017, Big Dalton Reservoir undergoes regular inspections to ensure its safety and functionality. The dam's last inspection in November 2020 affirmed its structural integrity, meeting regulatory standards set by the California Department of Water Resources and Safety of Dams. In case of emergencies, the reservoir is equipped with emergency action plans, although further details on their preparation and implementation are not specified in the available data.

Water resource and climate enthusiasts fascinated by the engineering marvels of dams and reservoirs will find Big Dalton an intriguing case study in flood risk management and water storage in the Los Angeles area. Its location in a densely populated region underlines the importance of maintaining and monitoring such critical infrastructure to safeguard communities and ecosystems against potential hazards and ensure a sustainable water supply for future generations.

Year Completed

1929

Dam Length

480

Dam Height

153

River Or Stream

Big Dalton Wash

Primary Dam Type

Multi-Arch

Surface Area

26

Hydraulic Height

141

Drainage Area

4.3

Nid Storage

1290

Hazard Potential

High

Nid Height

153
       
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.