Water gates (sluices) and dam gates

Sluices are installed where tributaries of a river join the main stream. They are normally open, but closed in case of flood risk to prevent the main stem river with rising water levels from flowing back into the tributaries. Likewise, sluice gates of a dam open and close for flood control, but are also operated to discharge water for several purposes such as irrigation, human consumption, and industrial use. In both cases, the opening and closing of the gates is enabled by limit switches that control upper/lower limit positions.