K-ATTTRAL WATERWAYS IN THE UIHTED STATES — HAETS. 555 



In this section, the project for a minimum channel depth of 9 feet 

 with a 250-foot width has been maintained for many years with 

 much success. The means employed have been the narrowing of the 

 high-water width of levees and the maintenance of the width at and 

 near low-water stages by bank protection and by supplementing these 

 methods by dredging on bars as they re-form. A few years ago 

 much reliance was placed on dredging as a sole means of improve- 

 ment, and nine large-capacity suction dredges were built and are 

 still being used; but the temporary nature of the work and the high 

 cost of maintenance of channels by this method led to the more de- 

 tailed study of bank protection. Between Cairo and New Orleans 

 there are said to be over 750 miles of caving banks, corresponding 

 fairly well to the length of one side of the river, and it is now believed 

 that the greater part of the sediment of the new shoals is from this 

 source. If the banks could be held from crumbling the river would 





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Fig. 1. — Heightening of Mississippi levees. 



soon scour for itself a channel ample for navigation, and, further- 

 more, the protection from floods by levees would then be considerably 

 simplified. A more serious effort is being made of late years to cut 

 down this supply of sand b}^ an annual extension of the bank protec- 

 tion (pi. 3, fig. 1), and by 1912 a total of 68.71 miles had been com- 

 pleted. This work at Albermarle Bend alone is estimated to diminish 

 the amount of material brought into the river annually by 11,000,000 

 cubic yards. The commerce on this river has dwindled to such a 

 small part of its former volume that protection against floods is now 

 the most serious problem of the engineers. Experience has shown 

 that this is best accomplished by levees, and since 1890 about half 

 of the appropriations for the lower Mississippi have been devoted to 

 that purpose. A new grade for levee height has recently been 

 adopted (1914) for all United States work; but many levees have 

 been built by State and local authorities, so but few are up to the 

 commission's level. When breaks occur it is almost invariably in 

 one of these low levees, and is usually caused by overtopping. 



