54 A TREATISE ON DREDGES AND DREDGING 



Hydraulic and ladder dredges can by cutting up snags, logs, 

 stumps and such obstructions remove them, but they are ill suited for 

 such work. The dredge that will remove these better than any other 

 is the dipper machine. The great pull of the hoisting engines on the 

 dipper, when it catches under a snag or log will raise it up even when 

 covered with a foot or two of soil. In excavating the shallow canals 

 through the Dismal Swamp in Virginia and North Carolina, great 

 numbers of logs and stumps were encountered and dipper dredges 

 were used exclusively on this work. However, owing to the excessive 

 number of sunken logs encountered, the work proved very expensive, 

 and some of the contractors lost money, due to this cause. On the 

 Mississippi River snag-pulling machines are used for removing old 

 snags and logs, making it possible for hydraulic dredges to follow 

 up these machines. 



For some jobs not only must special dredges be designed, as 

 previously stated, but it is sometimes necessary to design special 

 pipe lines, scows or even hoppers, in order to carry on the work 

 economically. 



It is almost impossible to give any rule for selecting a dredge 

 for canal, channels in large bodies of water, for rivers, harbors and 

 other improvements. The soil, the disposal of the material and 

 local conditions must govern it. All of the types of machines here 

 listed are and can be used. Sometimes on one job in America 

 hydraulic, ladder and dipper dredges have been used. Some have 

 also been of the hopper type, and some were self-propelling, while 

 others were non-propelling. 



In narrow canals dipper dredges are often used, depositing the 

 material on either bank. In wide streams scows are used to take 

 the spoil both from dipper and grapple dredges. For rivers and 

 harbors and for channels in bays and lakes all styles of machines 

 are used. For filling in behind bulkheads and for reclaiming low 

 lands the hydraulic dredge is a favorite machine, as the great quan- 

 tity of water distributes the material over a large area. When 

 bulkheads are not built, dipper machines are first used to throw 

 up a dike or levee and then a hydraulic machine for depositing the 

 material behind the dyke. 



Often dredged material has to be handled twice. It may be 

 first loaded onto scows, then dumped, and handled again to be placed 

 behind bulkheads, walls, or into piers. This rchandling is sometimes 

 done with suction dredges or by bucket machines. At times hopper 



