A weir, also known as a lowhead dam,'s a small overflow-type dam commonly used to raise the level of a river or stream. Weirs have traditionally been used to create mill ponds in such places. Water flows over the top of a weir, although some weirs have sluice gates which release water at a level below the top of the weir. The crest of an overflow spillway on a large dam's often called a weir. Function Weirs are used in conjunction with locks, to render a river navigable and to provide even flow… (More on Weir)