Upper Big Nemaha 1-B41 Reservoir Report
Nearby: Upper Big Nemaha J-15 South Branch 13
Last Updated: December 6, 2025
Located in Johnson County, Nebraska, Upper Big Nemaha 1-B41 is a local government-owned earth dam designed by USDA NRCS with a primary purpose of flood risk reduction.
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Summary
Completed in 1982, this structure stands at a height of 43 feet and has a hydraulic height of 39 feet, with a total length of 1416 feet. It has a storage capacity of 893 acre-feet, with a normal storage of 259 acre-feet, serving a drainage area of 2.9 square miles along the TR-Big Nemaha River.
Despite its important role in flood risk management, Upper Big Nemaha 1-B41 is rated as having a poor condition, with a significant hazard potential. The dam is regulated by the Nebraska Department of Natural Resources and undergoes regular inspections, with the last assessment conducted in May 2020. With a structural height of 46 feet and a spillway type not specified, this dam plays a crucial role in mitigating flood risks in the area, highlighting the importance of ongoing maintenance and monitoring to ensure its effectiveness in protecting the surrounding community from potential disasters.
Year Completed |
1982 |
Dam Length |
1416 |
Dam Height |
43 |
River Or Stream |
TR-BIG NEMAHA RIVER |
Primary Dam Type |
Earth |
Surface Area |
40 |
Hydraulic Height |
39 |
Drainage Area |
2.9 |
Nid Storage |
893 |
Structural Height |
46 |
Hazard Potential |
Significant |
Foundations |
Soil |
Nid Height |
46 |
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 1-B41