Frd No 21, also known as Upper Black Vermillion WS Dam 21, is a local government-owned structure in Frankfort, Kansas, designed by USDA NRCS for flood risk reduction along Ackerman Creek. Completed in 1971, this earth dam stands at a height of 29 feet with a hydraulic height of 26 feet, serving a primary purpose of flood risk reduction. With a storage capacity of 136.41 acre-feet and a surface area of 4.49 acres, Frd No 21 plays a crucial role in managing water flow in the region.

Located in Marshall County, Kansas, Frd No 21 has a low hazard potential and is currently rated as "Not Rated" in terms of condition assessment. While the dam does not have outlet gates or associated structures, it features an uncontrolled spillway with a width of 40 feet. The risk assessment for Frd No 21 indicates a moderate level of risk, with measures for risk management yet to be specified. As an essential part of the local water resource infrastructure, this dam contributes to the overall water management system in the region, ensuring the safety and protection of nearby communities from potential flooding events.