RECENT CONSTRUCTION OF MOVABLE DAMS. 271 



Dam No. 4 at Mirowitz. This was commenced in 1900. It consists of two needle 

 weirs and of a pass 184 feet wide closed by Boule gates. The needles are supported 

 by trestles, and the gates by frames lowered from a bridge and hinged to its down- 

 stream side, and arranged so that they can be hoisted above the highest floods. 

 These frames are 33 feet long and spaced in pairs about 6J feet apart, and carry i6J 

 feet on the sill. The gates are of iron buckled-*plates, each supported on a frame 

 with rollers. 



This arrangement of the dam was adopted, as it was desired to provide a highway 

 bridge across the river at that point. 



In America. The largest system of movable dams in America, and one which, 

 when ultimately completed, will compose the largest system in any country, is that 

 of the Ohio River. At present only one dam is actually in operation, that at Davis 

 Island, a few miles below Pittsburg, at the head of- the river. This was the pioneer of 

 movable dams in this country, having been completed more than twenty years ago in 

 the face of strenuous opposition from the navigation interests, who believed that any 

 structure in the river would seriously hamper traffic. One result of its construction 

 has been that these interests have since come to see that a suitable system of slack- 

 water is of the greatest benefit to commerce. Several other dams, Nos. 2, 3, 4, and 5, 

 are under construction and will be completed in a few years. All of these are to be of 

 the Chanoine type, with drift-chutes and regulating-weirs of bear-traps. Dam No. 6, 

 near Beaver, Pa., which was commenced in 1892, is to be completed in 1903. It con- 

 sists of a pass 600 feet long, closed by Chanoine wickets having a vertical height 

 above the sill of 13 feet 2 inches; two weirs of the old bear-trap type each 120 feet 

 long; and an A-frame weir also 120 feet long. The weirs have the same depth on 

 their sills as is provided on the sill of the pass. The lock chamber is 600 feet long 

 and no feet wide, closed by rolling gates. In addition to these dams several others 

 will be commenced before long, the project being to build dams below large cities and 

 the mouths of navigable tributaries first, and later to construct those between. 



Several of the tributaries of this river have already systems or parts of systems 

 of slack water navigation. At its head is the Monongahela River with an old system 

 of nine locks with fixed dams, and six more being constructed by the United States. All 

 the new ones will be of concrete, including the dams. On the Allegheny River, 

 the other head tributary, a lock and Chanoine movable dam are being built, and 

 two others with fixed dams proposed. Farther down, in the State of Ohio, is the 

 Muskingum River, with eleven locks and fixed dams, some of which are old, others 

 rebuilt by the United States. In West Virginia are the Little Kanawha River with 

 four locks and fixed dams belonging to a private corporation and one belonging to 

 the Government, and the Kanawha River with ten locks, two fixed dams and eight 

 Chanoine dams. The Big Sandy River follows with its lock and needle dam, and two 

 others nearing completion, as described in the Appendix. The Kentucky River has a 

 system of nine locks with fixed dams, and others in process of construction ; and Green 



