DRUM WICKETS AND BEAR-TRAPS. 



261 



in any case should have masonry foundation, and as the expense of constructing the 

 recess would probably be offset by the cube of masonry saved, the objection would 

 not often apply. The greatest objection to its application in its original form to 

 American rivers would be that the reaction of the overfall would carry debris under 

 the down-stream side of the wicket, preventing its proper bedding when lowered. 

 This might be overcome by the use of a sliding apron hinged to the top of the wicket, 

 or by sloping the masonry sharply away from the hinge on the down-stream side. 



SECTION OP DESFONTAINES DRUM DAM, RIVER MARNE. (1867.) 



In the Osage River type, as designed by Captain H. M. Chittenden, Corps of Engi- 

 neers, this objection has been removed, as the drum is shaped like a sector of a circle, 

 allowing no place for the lodgment of drift. This is gained, however, at some expense 

 of facility of maneuvers. In the Desfontaines drum the weight of the arms is prac- 

 tically balanced on the hinge, thus requiring only a small head to move them. In the 

 other the entire weight of the wicket has to be raised. It is necessary also to arrange 

 for the admission of water inside it so that it will not float up during floods, and at 

 the same time to arrange for the escape of this weight when it is desired to raise the dam. 



BEAR-TRAP DAMS. 



General. The bear-trap was the pioneer of movable dams, although it was prac- 

 tically unknown until within recent years. The first one was built by White & Hazard 

 in 1818 on the Lehigh River in the United States, and in the year following twelve 

 more were built. The type disappeared, however, for forty or fifty years, except 

 for occasional examples on lumbering streams, the next one applied to navigation being 

 that on the river Marne in France, where a gate was built 28 feet 8 inches long and gj 



