Upper Big Nemaha J-15a Reservoir Report
Last Updated: December 6, 2025
Located in Johnson, Nebraska, Upper Big Nemaha J-15a is a crucial earth dam designed by the USDA NRCS to mitigate flood risks and serve other purposes.
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Summary
Completed in 1973, this dam stands at a height of 22 feet and has a storage capacity of 66 acre-feet. With a low hazard potential and satisfactory condition assessment, it is regulated by the Nebraska Department of Natural Resources and undergoes regular inspections and enforcement to ensure its functionality and safety.
Situated on the TR-N FK BIG NEMAHA RIVER, Upper Big Nemaha J-15a plays a vital role in managing water resources in the area. Its stone core and soil foundation contribute to its structural integrity, with a maximum discharge capacity of 280 cubic feet per second. The dam covers a surface area of 3 acres and has a drainage area of 0.4 square miles, making it a significant feature in the local water management infrastructure.
Owned and operated by the local government, Upper Big Nemaha J-15a is a testament to collaborative efforts in water resource management. With its strategic design and regulatory oversight by the NE DNR, this dam stands as a reliable asset in flood risk reduction and water storage for the community. Its continued maintenance and adherence to state regulations ensure its effectiveness in safeguarding the surrounding environment and residents from potential water-related hazards.
Year Completed |
1973 |
Dam Length |
480 |
Dam Height |
22 |
River Or Stream |
TR-N FK BIG NEMAHA RIVER |
Primary Dam Type |
Earth |
Surface Area |
3 |
Hydraulic Height |
21 |
Drainage Area |
0.4 |
Nid Storage |
66 |
Structural Height |
26 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
26 |
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 J-15a