REMOVAL OF BARS AND OTHER OBSTRUCTIONS. 47 



matter in charge has reported that the plan has met with such success as to justify the 

 continuance of dredging. They claim that it has proved to be "a successful, eco- 

 nomical, and reliable means of low-water channel improvement." 



The report of the Mississippi River Commission for 1900 showed that during the 

 season of 1899 five dredges were employed. They cut about 62 miles of channel, aver-, 

 aging 105 lineal feet per hour. The channels were maintained without difficulty, the 

 season being very favorable. 



Location of Chute. In this work much depends on the skill with which the location 

 of the channel is made and also upon the water conditions. When the water remains 

 stationary, or steadily falls, a channel once opened remains navigable as long as there 

 is low water. If the location- is along lines that the current in seeking a crossing will 

 readily follow, it will not only remain open but will steadily improve. No established 

 rule can be laid down, however, for the location of this channel, it being necessary to 

 make a study of each case as it comes up and then so to place the dredge that it will 

 do the work effectively. The plan pursued in recent years has been to rapidly survey, 

 some time before extreme low water, the places most liable to require deepening. A 

 second survey is made at the time it is desired to begin operations. A study is then 

 made of the results of the surveys, followed by further examinations and observation, 

 and a decision is reached as to where the cut should be undertaken. Sometimes it 

 becomes necessary to abandon a chute after it is started, because the conditions prove 

 unfavorable to its maintenance, while in some of the channels excavated it is necessary 

 to remove additional material from time to time. 



Operation. To operate one of these dredges two wrought-iron anchor piles are 

 sunk by water-jet about 25 feet apart, and about 1000 feet above the point where 

 the dredging is to begin. Wire cables are run to them from the dredge, which then 

 commences pumping, slowly winding in the cables by steam-drums, the rate being 

 of course commensurate with the capacity of the pumps, an average being between 

 60 feet and 80 feet per hour. In windy weather it is necessary to set side piles to steady 

 the boat. After one cut is finished the piles are moved over for another cut, the dredge 

 dropped down stream, and the operations recommenced. The excavated material 

 is deposited through the discharge-pipes, several hundred feet away. 



The piles consist of hollow wrought-iron tubes, closed at the top, and open at the 

 bottom, with an attachment near the upper end for a aj-inch pressure hose. They 

 are sunk 15 feet to 20 feet into the sand, the mooring lines being attached to shackles 

 near the river-bed. A special boat carries the apparatus used for sinking them. 



In busy seasons the dredges are run 24 hours per day, and the cost per cubic yard 

 is given as from four-fifths of a cent to fifteen cents, depending on the looseness and 

 quantity of the material. The cost of the dredges is from $90,000 to $110,000, 

 according to size. 



Dimensions of Dredge. The dredge Iota, which is one of the most recent of the 

 Mississippi River fleet, has a hull of steel, 44 feet by 192 feet by 7 feet deep, and is self- 



