sluice formed by a number of thin needles held against a solid frame through water pressure as in a needle dam. Fan gate () This type of gate was invented by the Dutch hydraulic engineer in 1808. He was Inspector-General for Waterstaat (Water resource management) of the Kingdom of Holland at the time. The Fan door has the special property that it can open in the direction of high water solely using water pressure. This gate type was primarily used to purposely inundate certain regions, for instance in the case of the Hollandic Water Line. Nowadays this type of gate can still be found in a few places, for example in Gouda. A fan gate has a separate chamber that can be filled with water and is separated on the high-water-level side of the sluice by a large door. When a tube connecting the separate chamber with the high-water-level side of the sluice is opened, the water level, and with that the water pressure in this chamber, will rise to the same level as that on the high-water-level side. As there is no height difference across the larger gate, it exerts no force. However the smaller gate has a higher level on the upstream side, which exerts a force to close the gate. When the tube to the low water side is opened the water level in the chamber will fall. Due to the difference in the surface areas of the doors there will be a net force closing the gate. Designing the sluice gate Vertical rising sluice gates are the most common in open channels and can operate under two flow regimes: free flow and submerged flow. The most important depths in designing of sluice gates are: : upstream depth : opening of the sluice gate : the minimum depth of flow after the sluice gate : the initial depth of the hydraulic jump : the secondary depth of the hydraulic jump : downstream depth Flow under sluice gates could be described using energy–momentum concept by assuming that energy losses are negligible. The volumetric flow rate under vertical sluice gates could be estimated using the following equation: where represents the gravitational acceleration, and represents the channel's width. For free flow, where is the contraction coefficient, , which is the ratio of the jet width to the orifice opening width or the ratio of the cross-sectional area of the jet