548 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



streams have a total of about 2,600 miles of 10-foot navigation, and 

 70 streams give about 3,200 additional miles of navigation of from 

 6 to 10 feet during the greater part of the year, making a total of 

 about 5,800 miles of 6- foot and over river navigation. The greater 

 number of these streams flow into the Atlantic, but few of these have 

 more than 100 miles of such navigation. The longest connected river 

 system is the Mississippi and its principal tributaries, with about 

 2,500 miles of 6-foot navigation." (P. 29, "Transportation by 

 Water," Report of Commission of Corporations, 1909, Part I.) 



METHODS USED. 



With the exception of the protection of the ports on the Great 

 Lakes and the deepening of their approaches and connecting links, 

 the main work on these waterwaj^s has been in the nature of channel 

 development in the interior streams. It should be borne in mind that 

 in this work greater difficulties of an engineering nature have been 

 encountered than is usual in the streams of the older European coun- 

 tries, on account of the greater magnitude of the'work here and the 

 variety of the engineering problems presented, biU it Avill be noticed 

 that most of the successful works here have their prototypes in some 

 of the continental rivers, where longer experience than is available 

 here has eliminated many of the weaknesses, and enabled the later 

 worJfs to embrace the best of the Old World practice. It has thus re- 

 sulted that there is scarcely a river or harbor project anywhere in 

 the world in successful operation, the methods of which have not 

 been improved upon and used somewhere in this country. Within 

 recent years many new and original methods have also been adopted. 

 Foremost among these new means is the invention of the suction 

 dredge, the grapple, drag, and self-closing dredge buckets, which 

 liave reduced so markedly the cost of channel excavation of recent 

 years; the invention of new metliods of shore protection for rivers 

 with unstable banks ; the extensive use of reinforced concrete in lock 

 and dam construction; the adoption of movable dams; and the 

 enormous improvements in unloading machinery at terminals for ore 

 and bulky freight. 



The facilities for navigation presented by the natural waterways 

 of the United States place it in the first rank of the nations of the 

 world in this respect, and within the last decade much new work has 

 been done toward making these facilities more easily available for 

 use. 



LAKE SYSTEM OF INTERIOR WATERWAYS. 



It is on our northern border, where the chain of Great Lakes pre- 

 sents the most important system of interior natural waterways of 

 this country, that the most conspicuous example of national benefit 



