Grant B is a historic earth dam located in Jefferson County, Colorado, built in 1910 for the primary purpose of irrigation. The dam stands at 19 feet in height and spans 1200 feet in length, with a storage capacity of 250 acre-feet. Situated on the South Platte River, the dam also serves purposes such as flood risk reduction and recreation. Despite its age, Grant B has a low hazard potential and is deemed to be in satisfactory condition, last inspected in April 2016.

Owned privately, Grant B is regulated by the Colorado Department of Water Resources, with state jurisdiction, permitting, inspection, and enforcement in place. The dam's spillway is uncontrolled, with a width of 56 feet, and a maximum discharge capacity of 1052 cubic feet per second. With a surface area of 27 acres and a normal storage capacity of 130 acre-feet, Grant B contributes significantly to the water management system in the region. Its risk assessment is moderate, indicating a level 3 hazard potential.

Grant B, situated in the city of Bowmar, Colorado, within the Omaha District of the US Army Corps of Engineers, remains a key structure for water resource management in the area. Enthusiasts of water resources and climate will appreciate the rich history and functionality of Grant B, serving as a vital component in the irrigation network while also providing benefits for flood risk reduction and recreational activities.