but with a conical restriction prior to the gate leaf that focuses the water into a jet. They were developed in the 1940s by the United States Bureau of Reclamation to allow fine control of discharge flow without the cavitation seen in regular gate valves. Jet flow gates are able to handle heads up to 150 m. Physics The force on a rectangular flood gate can be calculated by the following equation: where: F = force measured in newtons (N) p = pressure measured in pascal (Pa) where: ρ is the density of fresh water (1000 kg/m3); g is the acceleration due to gravity on Earth (9.8 m/s2 ); h is the height of the water column in metres. A = area = rectangle: length × height measured in m2 where: length = the horizontal length of a rectangular floodgate measured in metres height = the height of a non-submerged flood gate from the bottom of the water column to the water surface measured in metres If the rectangular flood gate is submerged below the surface the same equation can be used but only the height from the water surface to the middle of the gate must be used to calculate the force on the flood gate. See also Flood barrier Tidal barrage Canal lock Thames Barrier Delta Works Oosterscheldekering References Sources US Army Corps of Engineers. (31 July 1995). Engineering manual 1110-2-2607, Planning and Design of Navigation Dams, Chapter 5, Overview of gate types. Retrieved 2008-04-14. External links DeltaWorks.Org – project in the Netherlands on floodgates Dams Hydrology Water transport infrastructure Flood barriers