Cottonwood-Green Valley Subws 50+40 #2 Reservoir Report
Last Updated: December 14, 2025
Cottonwood-Green Valley Subws 50+40 #2, located in Monona, Iowa, is a local government-owned earth dam designed by USDA NRCS and completed in 1966.
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Summary
With a height of 38 feet and a length of 928 feet, this dam serves multiple purposes including fire protection, stock, small fish pond, and flood risk reduction. It has a storage capacity of 92 acre-feet and covers a surface area of 4.6 acres, with a drainage area of 0.51 square miles.
Managed by the Iowa DNR, Cottonwood-Green Valley Subws 50+40 #2 has a low hazard potential and a moderate risk assessment rating of 3. The dam features an uncontrolled spillway and is primarily constructed with soil foundations. While the condition assessment is currently not rated, the dam is subject to state regulation, permitting, inspection, and enforcement. The risk management measures and emergency action plan status for this dam are currently not available, highlighting the importance of ongoing monitoring and maintenance for water resource and climate enthusiasts.
Overall, Cottonwood-Green Valley Subws 50+40 #2 plays a crucial role in water resource management in the area, providing essential services for fire protection, agriculture, and flood control. As part of the Rock Island District, this dam contributes to the conservation and preservation of water resources in Iowa, highlighting the collaborative efforts between local government agencies and federal partners like USDA NRCS. Monitoring the condition and risk assessment of this dam is essential for ensuring its continued functionality and safety in the face of changing climate patterns and water resource demands.
Year Completed |
1966 |
Dam Length |
928 |
Dam Height |
38 |
River Or Stream |
TR-COTTONWOOD CREEK |
Primary Dam Type |
Earth |
Surface Area |
4.6 |
Drainage Area |
0.51 |
Nid Storage |
92 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
38 |
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 50+40 #2