Upper Little Nemaha 21 Reservoir Report

Last Updated: December 5, 2025

Located in Lancaster, Nebraska, the Upper Little Nemaha 21 dam is a crucial flood risk reduction structure along the Little Nemaha River.


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Summary

Constructed in 1998, this earth dam stands at a height of 51 feet and stretches 2400 feet in length, with a storage capacity of 2439 acre-feet. Managed by Olsson Associates and regulated by the Nebraska Department of Natural Resources, the dam is designed to handle a maximum discharge of 15225 cubic feet per second, serving as a vital protective barrier for the surrounding rural community of Bennet.

With a hazard potential rated as high, the Upper Little Nemaha 21 dam undergoes regular inspections to ensure its structural integrity. The condition assessment conducted in August 2020 deemed the dam to be in satisfactory condition, meeting safety guidelines. While an Emergency Action Plan (EAP) was last revised in June 2015, there is room for improvement in terms of updating emergency contacts, preparing inundation maps, and conducting a comprehensive risk assessment. As a significant asset for flood control in the region, continued monitoring and maintenance are essential to uphold the dam's effectiveness in safeguarding the area from potential water-related disasters.

Year Completed

1998

Dam Length

2400

Dam Height

51

River Or Stream

LITTLE NEMAHA RIVER

Primary Dam Type

Earth

Surface Area

40

Hydraulic Height

51

Drainage Area

5.5

Nid Storage

2439

Structural Height

59

Hazard Potential

High

Foundations

Soil

Nid Height

59
       
Seasonal Comparison

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Dam Data Reference

Condition Assessment

Satisfactory
No 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

High
Dams 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.