330 happ. STREAM-CHANNEL CONTROL [Ch. 18 



for a distance of 962 miles from Pittsburgh to within 19 miles of 

 the confluence with the Mississippi River. The dams are of the over- 

 flow type, entirely submerged at high water, and all but one are fitted 

 with movable wickets or gates that can be raised or closed to main- 

 tain pool levels during periods of low flow, and lowered or opened to 

 pass high flows with relatively little obstruction to the current. There 

 are 42 low-lift locks with dams on which wickets can be lowered to 

 permit uninterrupted navigation at medium river stages; three locks 

 of moderate lift with dams that cannot be navigated, and one dam, 

 at the rock-floored 'Tails of the Ohio" near Louisville, which can be 

 navigated only at very high river stages, so that boats usually pass 

 through a canal about 2 miles long (U. S. War Department, 1939, pp. 

 134-137). 



The existing dams control water levels at low stages, but they are 

 not close enough to provide continuous channels 9 feet deep and 500 

 to 750 feet wide, as required for the barge traffic, without dredging 

 and contraction works. It is therefore expected that such supplemental 

 works will continue to be necessary. Contraction works consist mostly 

 of low dams to close secondary channels behind islands and thus con- 

 centrate the current, spur dikes to straighten wide, shallow reaches, and 

 bank revetments. 



The stream banks are generally stable, and bank erosion is not a 

 serious problem except in places along the lower Ohio where it is 

 locally severe. Most of the channel dredging and considerable bank 

 revetment are required in this section. Maintenance dredging during 

 the fiscal year 1948 amounted to 5.6 million cubic yards on the entire 

 Ohio River, about 94 percent of which was in the lower 58 percent of 

 the river length (U. S. Dept. of Army, 1948, p. 1810) . Most of the 

 dredging is believed to result from local sediment accumulations a short 

 distance downstream from areas of active bank erosion, it being re- 

 ported in 1935 that the pools showed no progressive silting, according 

 to comparisons of surveys made in 1911-1914 prior to construction 

 of most of the dams, and again in 1929 after the river had been com- 

 pletely canalized and about half the dams had been in operation 10 

 years or more (U. S. Congress, 1936, pp. 179-180). 



The lower parts of the Monongahela, Allegheny, and Kanawha 

 rivers are integral parts of the important Ohio waterway system, and 

 they are canalized by locks and dams similar to those on the Ohio. 

 Lower parts of the tributary Muskingum, Little Kanawha, Big Sandy, 

 Kentucky, Green and Cumberland river systems are also canalized 

 by low locks and dams, but these streams have less traffic, and shal- 

 lower channels are provided, and in some instances the locks are no 



