CHANOINE WICKET DAMS. 231 



up-stream side, and consisting of movable trestles, provided with floors or "aprons" 

 and a service track on which t!ic operating winch rolls. The trestles are placed 8 to 

 9 feet apart, and have their footway 2 to 3 feet above the pool. To raise the dam, 

 the trestles are first pulled up by the winch, using the short chains attaching each trestle- 

 head to the end of the apron of the next, one, and setting the aprons and track rails in 

 position as the maneuvers progress. The wickets are next pulled up by chains, which 

 connect the bottom of each wicket with the head of the nearest trestle, and when the 

 props are seated they are left "on the swing," that is, balanced on the horses in a hori- 

 zontal position. In this way the pass and weir wickets can all be raised without 

 obstructing the flow of the river to any appreciable extent. 



When all is ready, the wickets are righted and the current catches the butts and 

 forces them against the sill, thus closing the dam. This righting is done by pushing 

 the butts down with a pole, which has usually to be operated by the winch, if the 

 wickets are of any size. Another method, which is used on certain dams, consists in 

 one or two men' walking across the wickets and overbalancing each until it strikes the 

 current, when they jump on to the next one and repeat the maneuver until all are righted. 

 This is, however, attended with much danger, as if the men fall into the river they will 

 almost certainly be caught in the horses and be drowned. 



To regulate the pool, a few wickets with the corresponding trestles are lowered, 

 or they are put on the swing and kept in that position by holding the breech-chains in 

 the "stops" or chain sockets on the trestle-heads. When the discharge becomes low 

 the spaces between the wickets are closed by means of square timbers, pushed down 

 into them cornerwise. 



To lower the dam, the props are displaced by the tripping-bar, or, if Pasqueau 

 hurters are employed, the entire wicket is pulled up stream by the winch or from a boat, 

 until the prop falls over the shoulder into the groove and the wicket is then lowered. 

 On the weir this is done by pulling on the breech-chains; but on the pass, where the 

 lowering of the weir has reduced the pressure, the head of the wicket is pulled up 

 stream by a special grab-hook until the prop is free, when the hook is jerked off and the 

 water pushes the wicket down. This saves having first to put the pass wickets on the 

 swing, and permits of very rapid maneuvers. The breech-chains are then fastened 

 in the stops by pins and the trestles lowered. 



In dams dependent upon the tripping-bar, when the latter gets out of order, the 

 head of each wicket is pulled up stream from a boat till its prop is free, and the latter is 

 then pushed off the shoulder with a boat-hook from a skiff below and the wicket lowered. 



La Mulatifere Dam. This dam, completed in 1879, near Lyons, France, at the junc- 

 tion of the Saone and Rhone rivers, is one of the most advanced examples of a Chanoine 

 wicket dam. It was constructed under the direction of M. Pasqueau, and it was there 

 that he first introduced the double-stepped hurter, which has since been widely adopted. 



The pass of the dam is 340 feet in length, and is closed by wickets made of iron, 4.6 

 feet wide and 14.25 feet long, each being provided with a flutter-valve about 2.9 feet 



