Upper Big Nemaha J-15 Reservoir Report
Last Updated: December 6, 2025
Upper Big Nemaha J-15, located in Johnson, Nebraska, is a local government-owned earth dam completed in 1985 by USDA NRCS.
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Summary
This dam serves multiple purposes, including flood risk reduction, with a primary height of 25 feet and a max storage capacity of 40 acre-feet. The structure spans 606 feet in length and is regulated by the Nebraska Department of Natural Resources, ensuring state permitting, inspection, and enforcement to maintain its functionality.
With a fair condition assessment and low hazard potential, Upper Big Nemaha J-15 is designed to withstand potential risks while protecting the surrounding area. The dam's location on the TR-N FK Big Nemaha River contributes to its crucial role in managing water resources in the region. Despite its age, the structure continues to be monitored regularly, with the last inspection conducted in May 2017, ensuring its effectiveness in mitigating flood risks and preserving water quality in the area. Climate and water resource enthusiasts can appreciate the strategic design and maintenance efforts dedicated to this essential infrastructure.
Year Completed |
1985 |
Dam Length |
606 |
Dam Height |
25 |
River Or Stream |
TR-N FK BIG NEMAHA RIVER |
Primary Dam Type |
Earth |
Surface Area |
3 |
Hydraulic Height |
25 |
Drainage Area |
0.22 |
Nid Storage |
40 |
Structural Height |
29 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
29 |
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-15