CHAPTER VII. 

 CHANOINE WICKET DAMS. 



History. As the Poire"e dam was developed from the old-time plank dams, so the 

 Chanoine wicket dam is the evolution of another type. Gates with horizontal axes 

 fixed in the abutments had long been in use, as, for example, the valves used in the 

 dikes of Holland, while the weirs of certain dams on the Orb (1778) were formed of 

 shutters supported by hinges fastened to the floor Later on M. Thenard added the 

 prop, the hurter, and the tripping-bar, and the invention of M. Chanoine in 1852 raised 

 the axis of rotation to near the middle of the wicket, creating a type which has remained 

 almost unchanged. 



Description. The Chanoine wicket is a shutter hinged near its middle, supported 

 when up by a prop, and kept in position when revolving by a hinged frame known as 

 the horse. The lower end of the prop rests against a casting on the floor called the 

 hurter. When this end is moved from the support, the pressure of the water pushes 

 down the wicket, which turns on the horse until it lies flat behind the sill, with the 

 hurter, prop, and horse underneath. The part of the wicket above the axis of rota- 

 tion is called the head, or chase, and the part below, the breech or butt. 



In the heads of the wickets are sometimes placed other small wickets, known as 

 butterfly-valves, turning on an axis framed into the main wicket and kept closed by 

 latches. Their object is to afford a means of regulating the pool without having to 

 operate the large wickets, and they are opened or closed by means of a hook-pole 

 with which the dam-tender frees or closes the latches. They are not used in America, 

 as drift would prove troublesome, but they are in use on the Meuse, at La Mulatiere dam, 

 and elsewhere. 



The original idea of Chanoine was to place the axis at a point above the sill one- 

 third of the length of the wicket, this being the center of pressure of the water. As 

 the pool rose, this center would be changed to above the axis, and the wicket would 

 swing automatically, reducing the pool to its proper level, when the wicket would 

 swing back. All the early dams were constructed on this plan, being raised from boats 

 and lowered by tripping-bars but it was soon found that the wickets were too sensi- 

 tive, and while opening without trouble, they would not swing back without assistance, 

 or until the pool had fallen considerably. Moreover, when one wicket opened it 

 caused the lower pool to rise, creating more water below the dam and raising the center 

 of pressure on the down-stream side of the other wickets. This caused others to open, 



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