Johnston Dam Reservoir Report

Last Updated: December 7, 2025

Johnston Dam, located in Davis County, Iowa, was completed in 1972 and serves multiple purposes including fire protection, stock watering, and serving as a small fish pond.


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Summary

Owned privately, the dam is regulated by the Iowa Department of Natural Resources and is subject to state inspection and enforcement. With a height of 25 feet and a length of 510 feet, Johnston Dam has a storage capacity of 77 acre-feet, with a normal storage level of 48 acre-feet.

Situated on TR-Carter Creek, Johnston Dam has a surface area of 5.6 acres and drains a 0.17 square mile area. The dam's hazard potential is rated as low, with a moderate risk assessment score of 3 out of 5. The spillway type is uncontrolled, and the dam is primarily constructed of earth with a soil foundation. While the dam has not been assigned a condition assessment rating, it is noted to be in a not rated condition. Overall, Johnston Dam serves as a vital resource for water management and conservation in the area, contributing to the local ecosystem and providing essential services to the community.

Year Completed

1972

Dam Length

510

Dam Height

25

River Or Stream

TR-CARTER CREEK

Primary Dam Type

Earth

Surface Area

5.6

Drainage Area

0.17

Nid Storage

77

Hazard Potential

Low

Foundations

Soil

Nid Height

25
       
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.