Twelve Mile Creek Watershed Site D-41-A-5 Reservoir Report

Last Updated: December 12, 2025

Located in Grand River, Iowa, the Twelve Mile Creek Watershed Site D-41-A-5 is a flood risk reduction structure designed by the USDA NRCS and completed in 2006.


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Summary

This earth dam stands at a height of 36 feet and spans 464 feet, with a storage capacity of 168 acre-feet. The site is regulated by the Iowa DNR and is subject to state permitting, inspection, and enforcement, ensuring its effectiveness in mitigating flood risks in the area.

With a low hazard potential and a moderate risk assessment rating, the Twelve Mile Creek Watershed Site D-41-A-5 plays a crucial role in protecting the surrounding Union County community from flooding events. The uncontrolled spillway, with a width of 30,900 feet, allows for controlled water release during high flow periods. The structure's primary purpose is flood risk reduction, reflecting its importance in maintaining the safety and well-being of the local residents and environment.

As an essential part of the water resource infrastructure in the region, this dam serves as a testament to effective collaboration between local government, state agencies, and federal designers. With a focus on enhancing resilience to climate impacts, the Twelve Mile Creek Watershed Site D-41-A-5 stands as a symbol of proactive planning and adaptive management in the face of changing environmental conditions.

Year Completed

2006

Dam Length

464

Dam Height

36

River Or Stream

TR- TWELVE MILE CREEK

Primary Dam Type

Earth

Surface Area

6.5

Drainage Area

1.5

Nid Storage

168

Hazard Potential

Low

Foundations

Soil

Nid Height

36
       
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.