Johnson (Oscar) Dam Reservoir Report
Nearby: Kasparbauer Rager Dam
Last Updated: December 12, 2025
Johnson (Oscar) Dam, located in Harrison County, Iowa, is a private-owned structure designed by the USDA NRCS and completed in 2011.
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Summary
The dam serves multiple purposes, including flood risk reduction, grade stabilization, and recreation. It has a dam height of 49 feet and a length of 530 feet, with a storage capacity of 187 acre-feet and a drainage area of 0.75 square miles.
Managed by the Iowa Department of Natural Resources, Johnson Dam is regulated, permitted, and inspected by state authorities to ensure its safety and functionality. Despite being classified as a low-hazard structure with a "Not Rated" condition assessment, the dam plays a crucial role in protecting the surrounding area from potential flooding events. Situated on a tributary to Elk Creek, the dam also provides habitat for fish and wildlife, making it a valuable resource for conservation efforts in the region.
With its strategic location in Missouri Valley and its contribution to flood risk reduction, Johnson (Oscar) Dam stands as a vital infrastructure project in Iowa. Its construction and operation are supported by federal funding from the Natural Resources Conservation Service, highlighting the collaboration between private and government entities to manage water resources and enhance environmental sustainability. As a key piece of the state's water management infrastructure, the dam reflects a commitment to resilience and safety in the face of climate challenges.
Year Completed |
2011 |
Dam Length |
530 |
Dam Height |
49 |
River Or Stream |
Trib to Elk Creek |
Primary Dam Type |
Earth |
Surface Area |
6 |
Drainage Area |
0.75 |
Nid Storage |
187 |
Outlet Gates |
None |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
49 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Soldier River At Pisgah
|
112cfs |
Boyer River At Logan
|
417cfs |
Little Sioux River Near Turin
|
1040cfs |
Monona-Harrison Ditch Near Turin
|
158cfs |
Maple River At Mapleton
|
323cfs |
Missouri River At Decatur
|
15200cfs |
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.
Johnson (Oscar) Dam