Upper Big Nemaha J-12 Reservoir Report
Last Updated: December 6, 2025
Located in Johnson, Nebraska, Upper Big Nemaha J-12 is a local government-owned earth dam designed by the USDA NRCS with a height of 43 feet and a hydraulic height of 42 feet.
°F
°F
mph
Wind
%
Humidity
Summary
Completed in 1980, this dam serves multiple purposes including flood risk reduction and has a normal storage capacity of 55 acre-feet. With a drainage area of 1.2 square miles and a maximum discharge of 722 cubic feet per second, this structure plays a crucial role in managing water resources in the area.
Managed by the Nebraska Department of Natural Resources, Upper Big Nemaha J-12 has a low hazard potential and was last assessed to be in satisfactory condition in 2016. The dam is regulated, permitted, inspected, and enforced by the state agency, ensuring its safety and functionality. With a comprehensive emergency action plan in place, the structure is well-prepared to handle any potential risks or emergencies, meeting guidelines for risk management and ensuring the safety of surrounding communities.
As part of the flood risk reduction system along the TR-N FK Big Nemaha River, Upper Big Nemaha J-12 is a vital infrastructure asset in the region. With its stone core and soil foundation, the dam stands at a structural height of 44 feet and has a length of 715 feet. The dam's location, design, and capacity make it an essential component in protecting the local area from flooding and managing water resources effectively, showcasing the importance of sustainable infrastructure for climate resilience.
Year Completed |
1980 |
Dam Length |
715 |
Dam Height |
43 |
River Or Stream |
TR-N FK BIG NEMAHA RIVER |
Primary Dam Type |
Earth |
Surface Area |
11 |
Hydraulic Height |
42 |
Drainage Area |
1.2 |
Nid Storage |
306 |
Structural Height |
44 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
44 |
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-12