Upper Big Nemaha L-12 is a local government-owned earth dam located in Lancaster, Nebraska, designed by the USDA NRCS and completed in 1982. The dam stands at a height of 22 feet and has a storage capacity of 160 acre-feet, with a normal storage level of 34 acre-feet. Its primary purposes include flood risk reduction and other functions, serving the TR-N FK BIG NEMAHA RIVER. The dam has a low hazard potential and is in satisfactory condition as of the last inspection in September 2016.

Situated in the Omaha District, Upper Big Nemaha L-12 plays a crucial role in water resource management in the region, with a drainage area of 0.8 square miles and a maximum discharge capacity of 714 cubic feet per second. The dam's structural height reaches 25 feet, with a length of 535 feet and a surface area of 9 acres. It is regulated by the Nebraska Department of Natural Resources, with state permitting, inspection, and enforcement mechanisms in place to ensure its safe operation and maintenance.

For water resource and climate enthusiasts, Upper Big Nemaha L-12 represents a key infrastructure for flood control and water storage in the area. Its role in mitigating flood risks and managing water flow in the TR-N FK BIG NEMAHA RIVER watershed highlights the importance of such structures in ensuring water security and resilience to changing climate conditions. With its solid design and satisfactory condition, Upper Big Nemaha L-12 stands as a testament to effective water resource management and the collaborative efforts of local government and federal agencies in safeguarding the region's water resources.