Roller gate
Water
A gate rolled up or down inclined supporting rails by a hoist through sprocket chains around the ends of a cylinder. A crest gate consisting of a horizontal cylinder spanning between piers. Encircling each end of the cylinder is a cog wheel which engages a rack in each supporting pier. The gate is raised by a heavy chain or rope which winds around and over the top of the gate at one end and pulls upward parallel to the track.