THE WORK OF RUNNING WATER 87 



times, the current in the main channel is swift; but as the water 

 spreads beyond its channel over the adjacent flat, its velocity is 

 checked promptly, because its depth becomes less, suddenly. It 



I Fig. 88. Levees of the Mississippi in cross-section, four miles north of Don- 

 aldsonville, La. Vertical scale x 50. The horizontal line represents 

 sea-level. The bottom of the channel is far below sea-level at this point, 

 must, therefore, abandon much of its load then and there. Re- 

 peated deposition in this position gwes rise to the levees. 



The early population of Louisiana and Mississippi was largely 

 distributed in narrow belts along the levees of the Mississippi and 

 its tributaries and distributaries. The land here was high and dry 

 enough to be cultivated, very fertile, and close to streams, which 

 were the great highways of that time. 



Flood-plain meanders. A stream in an alluvial plain is likely 

 to wind about (meander) (Fig. 3, PL XVII, p. 64, and PL XIX, p. 80). 

 This may besaid to be the result of the low velocity of such a stream, 

 for the sluggish stream is easily turned aside. Were such a stream 

 made straight, it would become crooked again, and the manner of 

 change is illustrated by Figs. 89 and 90. If the banks be less firm at 

 some points than at others, as is always the case, the stream will cut 

 more at those points. If the shape of the channel is such as to direct 

 a current against a given point (6. Fig. 89), the result is the same, 

 even without difference of material. If a curve in the bank is once 

 started, it is increased by the current which is directed into it, and 

 as the current comes out of a curve, it is directed against the opposite 

 bank and develops a curve at that point. The water issuing from 

 this curve tends to make another, and so on. After being started, 

 meanders tend to become more and more pronounced (Fig. 90). 

 In the case shown in Fig. 2, PL XVII, p. 64, the neck of land be- 

 tween curves has become very narrow. When it is cut through, the 

 stream will abandon its wide curve. A later stage in the process 

 is shown in Fig. 3, of the same Plate. 



When the stream has cut off a meander, the abandoned part 

 of the channel may remain unfilled with sediment. If it contains 



