Upper 4s Ranch Reservoir Report

Last Updated: December 5, 2025

Upper 4s Ranch, located in Del Mar, California, is a privately owned dam on Lusardi Creek with a primary purpose of water supply for irrigation.


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Summary

Built in 1927, this arch-type dam stands at 28 feet high and has a storage capacity of 48.3 acre-feet. With a low hazard potential and satisfactory condition assessment, Upper 4s Ranch plays a crucial role in water resource management in the region.

Managed by the California Department of Water Resources (DWR) and subject to state regulations, inspections, and enforcement, Upper 4s Ranch is a key infrastructure for maintaining water supply and ensuring the safety of dams in the area. The dam's last inspection in June 2020 confirmed its sound structural integrity, further reinforcing its importance in the local water management system.

With its historical significance dating back almost a century and its ongoing role in supporting irrigation and water supply needs, Upper 4s Ranch serves as a vital resource for the community. As water resource and climate enthusiasts, understanding the infrastructure and management of dams like Upper 4s Ranch is essential for sustainable water management practices in California.

Year Completed

1927

Dam Length

246

Dam Height

28

River Or Stream

Lusardi Creek

Primary Dam Type

Arch

Surface Area

10

Hydraulic Height

25.3

Drainage Area

1.71

Nid Storage

48.3

Hazard Potential

Low

Nid Height

28
       
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.