Mcnab Reservoir Report

Last Updated: December 5, 2025

Mcnab is a privately owned dam located in Mendocino, California, specifically in the city of Hopland.


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Summary

Completed in 1947, this Earth-type dam stands at a height of 40 feet and serves multiple purposes including flood risk reduction, irrigation, and water supply. Its primary purpose, however, is flood risk reduction, providing a critical infrastructure for managing water resources in the region.

With a storage capacity of 96 acre-feet and a drainage area of 2.9 square miles, Mcnab plays a significant role in the management of water resources in the area. The dam is regulated by the California Department of Water Resources, Safety of Dams, ensuring that it meets necessary inspection and enforcement standards. Despite being classified as having a significant hazard potential, Mcnab is assessed to be in satisfactory condition as of its last assessment in September 2017.

Named after the nearby Mc Nab Creek, this dam is part of the broader water management infrastructure in the region and highlights the importance of maintaining and regulating such structures to mitigate flood risks and ensure water supply for various uses. For water resource and climate enthusiasts, Mcnab serves as a focal point for understanding the intersection of infrastructure, policy, and environmental conservation in managing water resources.

Year Completed

1947

Dam Length

830

Dam Height

40

River Or Stream

Mc Nab Creek

Primary Dam Type

Earth

Surface Area

7

Hydraulic Height

34.9

Drainage Area

2.9

Nid Storage

96

Hazard Potential

Significant

Nid Height

40
       
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.