Upper Big Nemaha 21-B, located in Lancaster, Nebraska, is a vital local government-owned flood risk reduction structure designed by the USDA NRCS. Completed in 1973, this earth dam stands at a height of 42 feet and has a storage capacity of 1890 acre-feet, serving the primary purpose of flood risk reduction for the TR-N FK BIG NEMAHA RIVER. With a drainage area of 5.5 square miles and a maximum discharge of 787 cubic feet per second, this dam plays a crucial role in managing water resources in the region.

The dam's condition assessment in 2017 rated it as satisfactory with a low hazard potential, indicating its reliability in flood mitigation efforts. The structure's inspection frequency is set at five years, with the last inspection conducted in June 2017. Managed by the NE DNR and regulated by the state, Upper Big Nemaha 21-B showcases the collaborative efforts between federal and state agencies in ensuring the safety and effectiveness of water resource management infrastructure. Its strategic location, coupled with its significant storage capacity and operational efficiency, highlights its importance in safeguarding the local community from potential flood risks and climate-related challenges.