Holbrook Reservoir Report

Last Updated: December 5, 2025

Holbrook, located in Ash Valley, California, is a privately owned dam that serves multiple purposes including flood risk reduction, irrigation, and water supply.


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Summary

Built in 1952, this earth dam stands at a height of 26 feet and has a storage capacity of 719 acre-feet, providing essential water resources for the region. The dam is situated on Ash Creek and has a drainage area of 14 square miles, with a surface area of 122 acres.

Managed by the California Department of Water Resources and regulated by the Safety of Dams agency, Holbrook is in a satisfactory condition with low hazard potential. Despite being a smaller dam, it plays a crucial role in mitigating flood risks and ensuring water availability for agricultural and residential needs in the area. The dam underwent its last inspection in August 2020, with a planned inspection frequency of once per year to ensure its continued functionality and safety.

Overall, Holbrook serves as a vital infrastructure in Lassen County, California, contributing to the region's water resource management and climate resilience efforts. With its strategic location and multiple purposes, the dam plays a significant role in supporting the local community's water supply needs and protecting against potential flooding events. Continuous monitoring and maintenance efforts ensure that Holbrook remains a reliable asset for water storage and flood risk reduction in the area.

Year Completed

1952

Dam Length

455

Dam Height

26

River Or Stream

Ash Creek

Primary Dam Type

Earth

Surface Area

122

Hydraulic Height

18

Drainage Area

14

Nid Storage

719

Hazard Potential

Low

Nid Height

26
       
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.