Emerald Lake 1 Lower Reservoir Report

Last Updated: December 5, 2025

Emerald Lake 1 Lower, also known as Lower Emerald Lake, is a privately owned dam located in Redwood City, California.


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Summary

Completed in 1885, this earth dam stands at a height of 57 feet and has a storage capacity of 45 acre-feet. With a primary purpose of water supply, this structure also serves for recreational activities in its 4-acre surface area. Situated on the Tr San Fran Bay river/stream and falling under the jurisdiction of the California Department of Water Resources, Emerald Lake 1 Lower is regulated, permitted, inspected, and enforced by state authorities to ensure its safety and functionality.

Despite its age, the dam's condition assessment in September 2017 deemed it satisfactory, with a high hazard potential due to its location and storage capacity. Regular inspections are conducted, with the last one taking place in March 2021 and emergency action plans in place. The dam's emergency contact information is updated, and it meets guidelines for risk management measures. While there are no inundation maps prepared or specific risk assessments outlined, the structure continues to provide essential water supply and recreational opportunities in the area, under the watchful eye of state regulators.

Year Completed

1885

Dam Length

280

Dam Height

57

River Or Stream

Tr San Fran Bay

Primary Dam Type

Earth

Surface Area

4

Hydraulic Height

52

Drainage Area

0.25

Nid Storage

45

Hazard Potential

High

Nid Height

57
       
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.