Dd No 1-1a (Vermillion Creek) is a local government-owned earth dam located in Marshall, Kansas, designed by J. Dale Steward for flood risk reduction purposes on the ROBIDOUX CREEK-TR. With a height of 26 feet and a length of 50 feet, this dam has a storage capacity of 178.7 acre-feet and a normal storage of 49.16 acre-feet. The spillway type is uncontrolled with a width of 30 feet, and the dam has a low hazard potential with a moderate risk assessment rating of 3.

Although the dam was last inspected in June 1996 and is currently not regularly inspected, it is reported to be in a not rated condition. Despite the lack of recent assessments, the dam's emergency action plan status, risk management measures, and inundation maps information remain undisclosed. With no state regulatory agency overseeing its operations, Dd No 1-1a poses a moderate risk that warrants further attention from water resource and climate enthusiasts to ensure its long-term safety and effectiveness in flood risk reduction for the surrounding area.