LEVEES. 89 



against it that its use was excluded, but now it is included in the levee specifications, 

 being placed in tufts 4 inches square set 2 feet apart. 



The growth of grass soon mats the covering together and makes a rather durable 

 protection, and on the land side it is preferable to apply nothing else because it is 

 important to be able to see the first signs of degradation. On the river slope at exposed 

 points, flat stones (water-wings) are employed; but their expense is too great for the 

 custom to be widely applied, and herbaceous or bushy vegetation is more general. Trees 

 with high trunks and heavy roots must be excluded as they may become dangerous 

 to the levee. 



A recent Government report says that the high water "has demonstrated very 

 clearly the value of a good sod which holds the slope in place, preventing sloughing 

 even when the levee is saturated; also, the fact that i to 3 slopes, when well sodded, 

 will withstand wave wash." 



In cases of extreme exposure pile-work and broken stone are much employed, 

 placed both parallel to the levee and in the form of spur-dikes. The protection of embank- 

 ments by thickly growing grasses is very general in Europe. Willows and other forms 

 of small trees are also planted for such purposes on the river slope, thus holding the 

 earth by their roots and breaking the wave-current by their branches. In some 

 countries straw is used, twisted into strong ropes, which are laid along the levee side 

 by side and held down by stakes. 



Maintenance. The maintenance of a levee includes all measures necessary for its 

 protection and welfare, not only when it is threatened but at all seasons. The cutting 

 of weeds and repairs of injuries by stock are as important as those of greater magnitude 

 during flood times. The measures for high-water protection are often, of necessity, 

 crude and of a temporary character. Usually they are carried out under the direction 

 of proper authority, but there are times when the population must take matters into 

 their own hands and hastily improvise such works as will protect their interests. 



Experience has shown that when levees break it is ordinarily from one of the fol- 

 lowing causes: 



(1) Insufficient height. 



(2) Leakage. 



(3) Sloughing. 



(4) Wave wash. 



(5) Cutting. 



(i) It is evident that a levee which is low enough to permit the water to flow over 

 its crown will, under ordinary conditions, be destroyed unless protection is promptly 

 given. At first the water merely trickles down the embankment, causing a slight 

 wash ; but this rapidly enlarges as the flow increases, until, finally, the waterfall pours 

 through the cut and tears out large masses of earth. Once well started it is difficult, 

 if not impossible, to stop it, so that it is far better to apply the remedy in advance of 

 the real danger. 



