CHANOINE WICKET DAMS. 

 The following are some examples of the sizes used in practice : 



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Remarks. The Chanoine dam after some fifty years of trial has proved on the 

 whole to be the type best adapted to large rivers subject to quickly rising floods, as it 

 is not easily disabled, can be maneuvered rapidly, and does not possess many loose 

 parts, such as accompany needle dams. The latter hold the water better, but on rivers 

 of any size the low water-flow is usually more than enough to compensate for leakage. 



One of the chief objections to the wicket dam is that it requires a very wide foun- 

 dation, in order to provide a base for the trestle bridge. Where this can be dispensed 

 with by operating from a boat the cost is much reduced. As to its practicability in 

 all cases, however, experience is conflicting. On part of the Davis Island dam, on the 

 Ohio River, a service bridge was originally provided, but it was destroyed one summer 

 by drift, since which time the maneuvering of that portion has been done entirely from 

 a boat. The wickets are 3 feet 9 inches wide and about 13 feet high. 



On the Mcuse, in Belgium, a boat is similarly used to raise the passes of the wicket 

 dams, but service bridges were provided for all the weirs, where they were deemed 

 necessary in order to control the wickets for the regulation of the pool. 



On the upper Seine, after experiments in using a boat for the weir, it was deemed 

 preferable to employ service bridges, a boat being found unsuited for night-work and 

 for easy regulation, and they were accordingly added. 



Where steam is employed there seems to be no objection to using a boat instead 

 of a bridge, at least for a pass. With a weir, however, a bridge is desirable, although 

 probably not necessary, as it allows an easier control of the wickets when they have 

 to be swung to regulate the pool. 



One objectionable feature of a service bridge is the floor sections, or aprons, as 

 when the dam is being lowered, as well as when it is down, the current almost inva- 

 riably works some of them free, so that their ends rise in the water and are then very 

 liable to be injured by drift or by boats. This trouble is noticeable on any movable 

 dam which has trestles provided with aprons, and it occurs chiefly on the weirs, since 

 there the currents are more violent than in the passes. Many expedients have been 

 tried to overcome it, but none has entirely succeeded. At La Mulatiere dam the 

 rails were braced together and hinged to the trestles, and a light floor of plank, of 

 a total width of 4 feet, was fastened between them. By this means the surface 

 exposed to the current was reduced and the weight considerably increased. This plan 



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