aja THE IMPROVEMENT OF RIVERS. 



wide and 5.1 feet long, operated by a hook pole in the usual manner. The sheathing 

 plates are -f f of an inch thick. The wickets are operated by a steam-engine, which 

 moves on a sen-ice bridge of trestles, the traek being (>\ feet above pool level. These 

 trestles are 9.8 feet apart and 22.3 feet high, and provided the first example where no 

 long bottom axle was used, pins being employed instead. By this arrangement the 

 depth of the recess behind the sill was reduced from 4 feet to 28 inches. 



It was here also that steam-power was first employed instead of the old methods 

 of hand-power, and the success of the work generally has had a. considerable influence 

 on wicket dams built since its completion. 



American Dams. At present only one river in .America, the Kanawha River, in 

 West Virginia, has a completed system of wicket dams. They are eight in number, 

 with lifts from 6} to 8} feet, the weirs being from 210 feet to 364 feet in width, and the 

 passes from 248 feet to 304 feet. The system was built between 1880 and 1898, and 

 in connection with two fixed dams affords a depth of 6 feet over about 90 miles of river. 



These dams are generally similar in design to those of Europe, and are operated 

 with trestle bridges and winches as before described. The locks are 55 feet wide and 

 342 feet between hollow quoins. 



On the Ohio River a system of locks and wicket dams has been commenced. 

 The first of these, that of Davis Island, just below Pittsburg, is the only one in opera- 

 tion, although others will soon be completed. The dam consists of a navigation pass 

 719 feet wide, and two weirs, affording a total opening of 1220 feet, which is closed 

 by 305 wickets, spaced 4 feet apart and provided with Pasqueau hurters. The pass 

 wickets are maneuvered from a boat with a steam-engine, the hoisting-line being 

 attached to a pole, with a hook at its end, which the operator catches in the butt of 

 the wicket. To lower the dam, the head of the wicket is pulled up stream until the 

 prop clears the shoulder, when it is released and falls with the current. One of the 

 weirs is maneuvered from a service bridge and the other by boat. The dam has also a bear- 

 trap drift chute, 52 feet wide, located between the pass and the first weir, and a fixed 

 dam separated from the second weir by an island. The lock is no feet wide and 600 

 feet long between the gates, the lift, when the pool below is at normal stage, being 6. i feet. 



Calculations Trestles. The trestles for wicket dams differ from those required 

 for other types in that the only direct load they sustain comes from the pull of rais- 

 ing or lowering the wickets, and from the weight of the crab and its car. The indirect 

 loads from drift, etc., are of course the same as elsewhere. 



The direct load is a variable quantity, and can only be approximated. Its maxi- 

 mum occurs when the wickets have to be pulled out of deposit or drift which may 

 have settled on them, and when the deposit is of any depth the winch is sometimes 

 unable to move them. The load should therefore be assumed as not less than the 

 maximum capacity of the winch, and it will usually be found sufficient to take it as 

 equal to two-thirds of the total water pressure on the wicket when standing, multi- 

 plied bv the angle between the chain and this pressure. The angle may be taken as 



