NAnjEAL WATERWAYS IN THE UNITED STATES HABTS. 663 



dams, and will provide for 6-foot navigation from the Ohio to Nash- 

 ville and there connect with the upper river to a point above Car- 

 thage, about 160 miles farther. The nine locks now in operation cost 

 $129,562 for maintenance in 1913. Commerce on the Cumberland 

 has been as follows, consisting largely of logs and lumber: 



Tons. [ Tons. 



1890 971, 563 1905 636, 237 



1895 ____ 321,137 1909 418,192 



1900 558, 371 | 1912 484, 744 



Of all the tributaries of the Ohio the Tennessee affords the greatest 

 variety of regimen. The lower section, of about 238 miles, is some- 

 what like the Mississippi — a slowly flowing, crooked stream of small 

 slope and comparatively large discharge, with low banks and soft, 

 easily eroded bed. Dredging is the form of improvement mainly 

 relied on for channel deepening. The next 238 miles is what is 

 known as the " mountain section," where swift currents, rocky beds, 

 high and rocky banks, rapids, and whirlpools are met with, requiring 

 rock removal, canalization, and lateral canals for their treatment. 

 In the upper section, of about 188 miles above Chattanooga, the bed 

 and banks are fairly permanent, but the shoals and rapids make 

 navigation difficult at low water. Here regulation by dikes and 

 excavation tunnels is used. The river is 652 miles long and has 

 tributaries which increase its channel length to 1,300 miles, all of 

 which can be used by steamboats, and 1,000 miles more can be used 

 by rafts and flatboats. Its drainage area is 44,000 square miles. The 

 work on this stream, which began as early as 1835, was done in a 

 rather disconnected way imtil 1909, when a single project for the 

 entire stream was proposed, providing for 6-foot navigation from 

 the mouth up to Chattanooga and 3-foot from Chattanooga to 

 Knoxville and the upstream end. The total estimated cost was 

 $13,000,000 and 12 years the estimate of time in which the work 

 should be completed for most economical results. Work is now under 

 way on this project. In the lowest section the most formidable ob- 

 struction is a rock shoal known as Big Bend. This work is note- 

 worthy, as specially designed drill rafts are used for drilling and 

 breaking up the bottom (pi. 6, fig. 1), and a crane boat, with a 90-foot 

 boom and a grapple bucket, are used to remove the blasted material 

 (pi. 6, fig. 2), the purpose being to place it in training walls on each 

 side of the cut to act as guides for low-water navigation, and thus 

 avoid handling a large part of the material by barge (pi. 7, fig. 1). 

 This work is now under way. The dredging and rock removal under 

 the new project was estimated to cost $600,000 in addition to previous 

 work. Already $534,000 has been expended on this section to secure a 

 5-foot depth of channel, and the additional amount is required to get 

 the 6-foot depth necessaiy and complete the deepening of the remain- 



