Arp Dam Reservoir Report

Last Updated: December 14, 2025

Arp Dam, located in Johnson County, Iowa, is a privately owned earth dam constructed in 1970 by the USDA NRCS.


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Summary

With a height of 31 feet and a length of 322 feet, the dam serves multiple purposes including fire protection, stock, small fish pond, and recreation. The dam has a storage capacity of 42 acre-feet and covers a surface area of 2.9 acres, with a drainage area of 0.13 square miles.

Managed by the Iowa Department of Natural Resources, Arp Dam is regulated, permitted, inspected, and enforced by state authorities to ensure its safety and functionality. The dam has a low hazard potential and a moderate risk rating, making it a key infrastructure for water resource management in the area. Despite not being rated for its condition, the dam continues to provide essential services to the community, including water storage and environmental conservation along the TR-Knapp Creek.

In the event of an emergency, the dam's emergency action plan and risk management measures are crucial for ensuring public safety and minimizing potential risks. With its strategic location and design, Arp Dam plays a significant role in supporting water supply, recreational activities, and wildlife habitat preservation in the Coralville Reservoir area.

Year Completed

1970

Dam Length

322

Dam Height

31

River Or Stream

TR-KNAPP CREEK

Primary Dam Type

Earth

Surface Area

2.9

Drainage Area

0.13

Nid Storage

42

Hazard Potential

Low

Foundations

Soil

Nid Height

31
       
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.