70 THE IMPROVEMENT OF RIVERS. 



pins have been largely employed for fastening binding pieces, and form a much more 

 satisfactory method than wires in swift currents. 



Mattress revetment is the chief method employed along the Mississippi and 

 Missouri rivers. There brush grows in abundance, and in spite of continued denuda- 

 tion for these works the supply has not been exhausted, as cotton-wood and willows 

 spring up rapidly, so that it is the cheapest material for use. Out of the abundance 

 and cheapness of this material has grown the practice of its use, in connection with 

 stone, also fairly plentiful, as a revetment for banks in this country. 



In regard to these works it is stated* that "The bank revetment work (on the 

 lower Mississippi River) is probably more extensive than any like engineering construc- 

 tion in the world. A mattress 300 feet wide by 1200 feet long represents a superficial 

 area of about 8 acres, and when one realizes that this vast willow carpet, over a foot 

 thick, is placed on the bottom of the river in depths of from 40 to'ioo feet, and against 

 currents of from 5 to 8 feet per second, the difficulty of the enterprise will be appre- 

 ciated. Though much of the revetment from Cairo to New Orleans has needed repairs 

 from year to year, and in some reaches has required renewal as a whole, it may be said 

 to have been eminently successful in the protection of harbor fronts and the preven- 

 tion of cut-offs and outlets, and fairly so in the control of bank-caving, and the resulting 

 change in position and flow of the river. 



"At some points, where the material of the bank was friable and the currents very 

 strong, the earlier forms of revetment proved too light and were entirely swept away, 

 the shore line continuing to move back. Also considerable reaches of protection work 

 needing repairs and reinforcement at the ends have been destroyed because of the lack 

 of funds, due to the failure of appropriations, etc. But in the later work the results 

 have been beneficial and satisfactory, and the loss but slight." 



It is not customary to carry the protection to the full height of the bank, particu- 

 larly where this is above the highest floods, and recourse is had in the upper portions 

 to sodding. In America this has been done only to a very limited extent, but the 

 practice is quite common abroad. This kind of revetment is made by means of pieces 

 of sod cut into squares or rectangular figures and placed in courses normal to the slope 

 where the latter is steep, and parallel to it where it has a gradual inclination. In certain 

 localities Bermuda grass has been used, the sprigs being placed from 6 inches to a foot 

 apart. As this grass possesses a phenomenal vitality, the roots spread rapidly and 

 form a dense sod in the course of a year or two, completely covering the bank. 



As has been mentioned, one form of protection, called continuous revetment, 

 contemplates the entire covering of the section of bank under treatment, while another, 

 known as spur-revetments and bank-heads, has in view the covering of isolated portions 

 only, depending -upon the works for warding off damaging currents along the spaces 

 between them. The continuous revetment is in most general use, both at home and 

 abroad, but there are a number of examples of the other form along the Missouri. 



* Bank Revetment on the Lower Mississippi, Am. Soc. C. E., 1896, II. Copp6e. 



