Patterson Reservoir Report

Last Updated: December 5, 2025

Patterson is a significant earth dam located in Alameda, California, with a primary purpose of water supply.


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Summary

Completed in 1962, this dam stands at a height of 100 feet and has a hydraulic height of 99.83 feet, providing a storage capacity of 46 acre-feet. The dam is regulated by the California Department of Water Resources (DWR) under the Safety of Dams program, with state jurisdiction and enforcement in place to ensure its safety and proper maintenance.

Despite its fair condition assessment as of September 2017, Patterson poses a significant hazard potential due to its location and structural specifics. The dam is subject to regular inspections with a frequency of once a year, with the most recent one conducted in February 2021. The dam's emergency action plan (EAP) status, risk assessment, and management measures are currently not available, indicating a potential area for improvement in terms of emergency preparedness and response.

Owned and operated by the local government, Patterson serves as a crucial water resource in the region, contributing to water supply needs in the area. With its strategic location and design, this dam plays a vital role in managing water resources and ensuring a reliable supply for the community. Continuous monitoring and adherence to safety regulations are essential to mitigate any potential risks associated with the dam and to maintain its functionality for the benefit of the local population.

Year Completed

1962

Dam Length

1306

Dam Height

100

River Or Stream

Offstream

Primary Dam Type

Earth

Surface Area

2

Hydraulic Height

99.83

Nid Storage

46

Hazard Potential

Significant

Nid Height

100
       
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.