Control gates regulate water flow between two areas as a means to control flooding, reduce runoff or maintain different water levels in adjacent area of a waterway. There are several different designs, each with advantages and drawbacks. All water control gates work by channeling water through a confined space that can be blocked or opened at will.
Sluice Gate - A sluice gate is a type of water control gate used in open channels. A rectangular gate made of wood or metal slides up and down along tracks within a larger wall or dam spanning the waterway. The area on either side of the sluice gate also has a smooth, solid bottom. The heavy gate is powered by hydraulics, or mechanically with a trapezoidal bolt or pin rod. When correctly calibrated, sluice gates can be used to measure the flow of water.
Screw Gate - Another type of water control gate used to regulate runoff into and out of drainage pipes is the screw gate. Similar in structure to a sluice gate, it has a round gate mounted on vertical tracks that covers the end of a cylindrical drainage pipe. The gate is attached to a threaded screw, and raised or lowered by means of a wheel that feeds the screw up or down when turned clockwise or counterclockwise. Screw gates require close monitoring during use and do not prevent sediment loss from runoff, making them undesirable in many applications.
Flashboard Riser - The flashboard riser is a style of passive water control gate used on drainage pipes. The cylindrical, half-moon shaped frame attaches to the end of the drainage pipe. The open side of the crescent has vertical channels designed to accept wooden boards of a certain length. The height of the gate is determined by how many boards are dropped into the channels to stack up at the bottom of the gate. Water does not flow in or out until the water level gets higher than the top board, and sediment is trapped in the gate instead of running off.
Drop-Log - Drop-log or stoplog control gates use the same principal as the flash-board riser, but are designed for use on open waterways instead of drainage pipes. A dam or wall across the waterway has an opening in the center with vertical channels to accept boards. Boards dropped into the channels stack up to the desired height. The water level on either side of the gate can fluctuate due to runoff or tides without affecting the other side, unless the level goes higher than the height of the top board.