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Show , rivers naturally seek ( meandering meamdering ) 140 courses , with ( re- re ) sultant swifter current and ( well-defined welldefined ) channels next to the concave shore , if they are to arrive finally at a destination , reverse ( carves ctirves ) are necessary . With few exceptions crossing bars are coincident with all such reversals . It is apparent that the reversal of the current from one bank to the other is the primary cause of crossing bars . ( Photo 5 , Compl . Exhibit 145 . ) These bars extend across the river diagonally and average in length from 1,000 feet to more than 3,000 feet . It is evident that when the river is at flood stage the channel is full from bank to bank . Velocities in the cross sections are , however , . known to vary within wide limits , even ( where irhere ) the cross section is regular and the channel straight . Each change in the cross section or direction of the river is attended by a redistribution of velocities in the cross section and a change in the direction of the thread of ( maxi- maxi ) mum velocities . These changes in velocity give rise tp the formation of whirlpools eddies and backwater , , , with the resultant decrease in the velocity and a ( par- par ) tial or complete deposition of sediment carried in ( sus- sus ) pension or as bed load . ( When Wben ) the direction of current is changed as a result of a reversal of curvature of the channel , there is change in the distribution of ( veloci- veloci ) ties . The thread of maximum velocity which , as a result of centrifugal force , follows the concave bank is diverted diagonally across the channel and ( down- down ) stream . The reduction in the velocities parallel to the thread of the current is apparently sufficient to |
