Johnson Dam Reservoir Report

Last Updated: December 13, 2025

Johnson Dam, located in Mills County, Iowa, is a privately owned structure designed by NRCS for fire protection and as a small fish pond.


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Summary

Completed in 2006, the earth dam stands at a height of 30 feet and spans 513 feet in length, with a storage capacity of 83 acre-feet. Situated on TR- Keg Creek, the dam serves as a crucial water resource for the surrounding area, with a normal storage capacity of 54 acre-feet and a surface area of 5.1 acres.

Managed by the Iowa DNR, Johnson Dam is regulated, permitted, inspected, and enforced by the state. Classified with a low hazard potential and a moderate risk assessment, the dam meets guidelines for emergency action plans and risk management measures. While the spillway is uncontrolled with a spillway width of 1 foot, the dam's condition assessment is currently not rated, with no recent inspection date available. Despite this, Johnson Dam remains a vital asset for water storage and conservation in the region.

For water resource and climate enthusiasts, Johnson Dam offers insights into the intersection of infrastructure, water management, and environmental stewardship. With its strategic location, design features, and regulatory oversight, the dam provides a tangible example of how private entities can contribute to sustainable water practices. As part of the broader network of dams and reservoirs in the area, Johnson Dam plays a crucial role in ensuring water security, flood protection, and habitat preservation for the local ecosystem.

Year Completed

2006

Dam Length

513

Dam Height

30

River Or Stream

TR- KEG CREEK

Primary Dam Type

Earth

Surface Area

5.1

Drainage Area

0.36

Nid Storage

83

Hazard Potential

Low

Foundations

Soil

Nid Height

30
       
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.