Hannen Lake Dam Reservoir Report
Nearby: Steinbeck Dam Jdw Dam
Last Updated: December 13, 2025
Hannen Lake Dam, located in Benton County, Iowa, is a local government-owned structure designed by the Howard R Green Co.
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Summary
The dam, completed in 1959, serves a primary purpose of recreation and has a normal storage capacity of 390 acre-feet. With a dam height of 35 feet and a length of 600 feet, it impounds the waters of TR-COON CREEK to create a surface area of 39 acres for recreational activities.
Managed by the Iowa Department of Natural Resources, Hannen Lake Dam is regulated, permitted, inspected, and enforced by state agencies to ensure its safety and compliance with standards. The dam has a low hazard potential and a satisfactory condition assessment as of the last inspection in June 2019. Despite its low risk, the dam is considered to have a moderate overall risk level, indicating the need for continued monitoring and risk management measures.
Situated in the Detroit District of the US Army Corps of Engineers, Hannen Lake Dam has not been modified in recent years and does not feature significant outlet gates or locks. While the dam's spillway is uncontrolled with a width of 5 feet, it has not experienced maximum discharge events. Overall, Hannen Lake Dam provides a crucial recreational resource for the community while maintaining a focus on safety and risk management in its operation and maintenance.
Year Completed |
1959 |
Dam Length |
600 |
Dam Height |
35 |
River Or Stream |
TR-COON CREEK |
Primary Dam Type |
Earth |
Surface Area |
39 |
Drainage Area |
0.96 |
Nid Storage |
886 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
35 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Iowa River At Marengo
|
818cfs |
Iowa River Near Belle Plaine
|
966cfs |
Big Bear Creek At Ladora
|
56cfs |
Salt Creek Near Elberon
|
42cfs |
Walnut Creek Near Hartwick
|
13cfs |
Richland Creek Near Haven
|
12cfs |
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Hannen Lake Dam