Upper Big Nemaha 18-A Reservoir Report
Last Updated: December 6, 2025
Upper Big Nemaha 18-A is a vital flood risk reduction structure located in Johnson, Nebraska, along the TR-Hooker Creek.
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Summary
Built in 1970 by the USDA NRCS, this earth dam stands at a height of 41 feet and has a storage capacity of 538 acre-feet. With a normal storage capacity of 133 acre-feet, the dam serves the primary purpose of flood risk reduction, protecting the surrounding area from potential inundation.
Managed by the Natural Resources Conservation Service, Upper Big Nemaha 18-A has a low hazard potential and is in satisfactory condition, as assessed in May 2019. The dam's inspection frequency is set at every 5 years, ensuring its continued functionality and safety for the community. With its stone core and soil foundation, this structure plays a crucial role in mitigating flood risks and safeguarding the local environment against potential water-related disasters.
Situated under the regulatory jurisdiction of the NE DNR, Upper Big Nemaha 18-A is a key component in the flood risk management strategy of the region. With a maximum discharge capacity of 640 cubic feet per second and a surface area of 15 acres, this earth dam is a critical piece of infrastructure that contributes to the resilience of the local water resource system. Its presence highlights the importance of proactive measures in addressing climate-related challenges and underscores the collaborative efforts between local government agencies and the USDA NRCS in safeguarding communities against the impacts of extreme weather events.
Year Completed |
1970 |
Dam Length |
739 |
Dam Height |
41 |
River Or Stream |
TR-HOOKER CREEK |
Primary Dam Type |
Earth |
Surface Area |
15 |
Hydraulic Height |
39 |
Drainage Area |
1.5 |
Nid Storage |
538 |
Structural Height |
43 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
43 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
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.
Upper Big Nemaha 18-A