Pony Creek Watershed Site 21 Reservoir Report

Last Updated: December 14, 2025

Pony Creek Watershed Site 21, located in Mills County, Iowa, is a local government-owned earth dam constructed in 1971 by the USDA NRCS for flood risk reduction along Pony Creek.


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Summary

The dam stands at a height of 75 feet and has a storage capacity of 3,660 acre-feet, serving a drainage area of 13.84 square miles. With a surface area of 83.2 acres, the dam plays a crucial role in mitigating flood risks in the region.

Managed by the Iowa DNR, Pony Creek Watershed Site 21 is classified as a high hazard potential dam with a satisfactory condition assessment as of August 2019. Despite its moderate risk assessment rating, the dam has not undergone any modifications in recent years and is inspected biennially to ensure its structural integrity and functionality. The dam's spillway, with a width of 4 feet, is uncontrolled, posing potential risks during high discharge events.

For water resource and climate enthusiasts, Pony Creek Watershed Site 21 serves as a vital infrastructure for flood risk reduction and water management in the region. As part of the larger Pony Creek watershed, this dam contributes to the overall resilience of the area against flooding events and provides essential protection to downstream communities. Its role in safeguarding the local ecosystem and infrastructure underscores the importance of continued monitoring and maintenance to ensure its effectiveness in the face of changing climate patterns.

Year Completed

1971

Dam Length

968

Dam Height

75

River Or Stream

PONY CREEK

Primary Dam Type

Earth

Surface Area

83.2

Drainage Area

13.84

Nid Storage

3660

Hazard Potential

High

Foundations

Soil

Nid Height

75
       
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.