Cottonwood-Green Valley Subws 99+50 #2 Reservoir Report
Last Updated: December 13, 2025
Located in Monona, Iowa, the Cottonwood-Green Valley Subws 99+50 #2 dam serves multiple purposes including fire protection, stock watering, and small fish pond maintenance.
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Summary
Built in 1966 by the USDA NRCS, this earth dam stands at a height of 26 feet and spans 478 feet in length. With a storage capacity of 54 acre-feet, the dam covers a surface area of 2.8 acres and drains a 1.32 square mile watershed area.
Managed by the Iowa Department of Natural Resources, this dam on the TR-MAPLE RIVER is regulated, permitted, and inspected by the state. Despite its low hazard potential, the dam is considered to have a moderate risk level. The emergency action plan status for this structure remains unreported, indicating a gap in preparedness for potential incidents. Overall, the Cottonwood-Green Valley Subws 99+50 #2 dam plays a crucial role in water resource management and flood risk reduction in the region, highlighting the importance of monitoring and maintaining such structures for the safety and well-being of local communities.
Year Completed |
1966 |
Dam Length |
478 |
Dam Height |
26 |
River Or Stream |
TR-MAPLE RIVER |
Primary Dam Type |
Earth |
Surface Area |
2.8 |
Drainage Area |
1.32 |
Nid Storage |
54 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
26 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Maple River At Mapleton
|
323cfs |
Little Sioux River Near Turin
|
1040cfs |
Monona-Harrison Ditch Near Turin
|
158cfs |
West Fork Ditch At Hornick
|
80cfs |
Soldier River At Pisgah
|
112cfs |
Missouri River At Decatur
|
15500cfs |
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.
Cottonwood-Green Valley Subws 99+50 #2