Undershot Water Wheel

An undershot water wheel is a water wheel turned by the current of a stream flowing past paddles fixed around its lower rim, drawing on the speed of the moving water rather than its weight. It needs only a modest drop in the streambed, so it could be used on flatter rivers where an overshot design was impractical, but it converts a smaller share of the available energy into useful work and was generally the least efficient of the traditional water wheel designs. Undershot wheels were widely used for early grain mills and other simple industrial power before more efficient overshot wheels and later water turbines replaced them on sites with enough fall to support them.