Hagmaier South Reservoir Report

Last Updated: December 5, 2025

Hagmaier South, located in Marin, California, is a federal-owned dam managed by the National Park Service.


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Summary

Built in 1944 on Olema Creek, this earth dam stands at a height of 24 feet, with a storage capacity of 20 acre-feet. With a significant hazard potential, the dam's condition assessment is currently listed as "Not Available," and its last inspection was conducted in September 2015.

Despite being under federal ownership and regulation, Hagmaier South does not fall under state jurisdiction or permitting. The dam serves primarily to control water flow and storage in the area, with a normal storage capacity of 13 acre-feet. While the dam's risk assessment, emergency action plan, and inundation maps are not readily available, the National Park Service is responsible for its operations, inspections, and emergency preparedness.

Located in the district of San Francisco, Hagmaier South plays a crucial role in water resource management in the region. With its historical significance dating back to World War II, the dam continues to be a key structure in the National Park Service's portfolio. Climate and water resource enthusiasts would find Hagmaier South's unique characteristics and management under federal oversight intriguing in the context of sustainable infrastructure development and climate adaptation efforts.

Year Completed

1944

Dam Height

24

River Or Stream

OLEMA CREEK

Primary Dam Type

Earth

Surface Area

2.3

Drainage Area

150

Nid Storage

20

Hazard Potential

Significant

Nid Height

24
       
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.