Little Onion Dam Reservoir Report

Last Updated: December 15, 2025

Little Onion Dam, located in Humboldt, Nevada, is a private-owned structure designed by Sprout Engineering for irrigation purposes along Alder Creek.


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Summary

The earth dam stands at 31 feet high with a hydraulic height of 26 feet and a structural height of 35 feet, providing a maximum storage capacity of 325 acre-feet. With a spillway width of 36 feet and a maximum discharge of 4000 cubic feet per second, the dam serves multiple purposes including fire protection, stock, small fish pond, irrigation, and recreation.

The dam, built in 1959 and last inspected in June 2019, has a significant hazard potential and fair condition assessment. Despite its age, the structure meets regulatory standards set by the Nevada Department of Water Resources, with regular inspections and enforcement ensuring its safety. While the risk assessment categorizes it as moderate, with a risk score of 3, the dam's emergency action plan and inundation maps status remain unclear. Little Onion Dam plays a crucial role in water resource management in the region, highlighting the intersection of infrastructure, climate adaptation, and environmental stewardship.

Years Modified

1959 - Hydraulic, 1959 - Structural

Dam Length

710

Dam Height

31

River Or Stream

ALDER CREEK

Primary Dam Type

Earth

Surface Area

30

Hydraulic Height

26

Nid Storage

325

Structural Height

35

Outlet Gates

Slide (sluice gate) - 1

Hazard Potential

Significant

Foundations

Rock

Nid Height

35
       
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.