LEVEES. 87 



pose in that it is an excellent way of investigating the character of foundation soil, 

 and furnishes, when filled with selected earth and tamped, a diaphragm through which 

 the water will not seep. This feature in levees has caused much discussion among 

 engineers, some claiming that it is of little value, or is even hurtful, while others con- 

 tend that it is a useful and even necessary precaution against destruction. Mr. Starling 

 says: "Generally levee engineers, while they recognize that muck-ditches do a certain 

 amount of good, as they have very limited means, prefer to spend their money above 

 ground. They therefore give the ditches small dimensions, using them, in fact, rather 

 for exploration than for any other purpose," 



Mr. Hewson says: "The practice of cutting out a trench for the puddle, or 'muck- 

 ditch' as it is called on the Mississippi, in the natural surface of the ground is generally 

 useless, and sometimes positively mischievous. When retentive subsoils exist under 

 the base of the proposed bank, then it is certainly a clear gain in stanchness to run 

 down the puddle-wall of the levee to a bond with the underlying impervious earth. 

 But the experience along the shores of the Mississippi leads to the presumption that, 

 in those cases where the sand does not commence on the surface, a ditch of 3 feet deep 

 is more likely to present a bottom of sand than of loam or clay. The rationale of those 

 muck-ditches rests on their usefulness in preventing leakage; and therefore, suppos- 

 ing the ditch and wall carried up regularly with a puddle, those ditches in a great 

 majority of cases failing to reach a more retentive soil than at the surface of the ground, 

 involve in all those cases an utterly resultless waste of money. Besides, to undertake 

 to prevent leakage through the porous earths of the natural shores of the river is a 

 hopeless labor; and so far as the strength and durability of the levees are concerned 

 is a labor also perfectly useless. It accomplishes nothing whatever for the artificial 

 embankment. But in some cases these muck-ditches are, as already stated, mis- 

 chievous. Across those lagoons or creeks which are dry during periods of low water 

 the foundation for banks consists generally of a hard crust of clay for a few feet thick, 

 overlying quicksands or thin puddles. These crusts, like the grillage of timbers used 

 for the foundations of some engineering works, are highly valuable in those situations, 

 by diffusing the weight of the superincumbent levee over a wide bearing; and thus, 

 though unequally loaded by the necessary cross-section of the levee, assist, in pro- 

 portion to their strength, in distributing that bearing equally. This, where not suffi- 

 cient to obviate the sinkage altogether, reduces it considerably ; and in bringing a large 

 area to act in the resistance, assists in guaranteeing, with the least possible sinkage, 

 and therefore the least possible loss of work and money a finally well-sustained foun- 

 dation. The muck-ditch, however, cuts this natural platform for the levee in two 

 parts; and over this cut, the greatest weight, that at the crown, pressing vertically, 

 acts as with a leverage in bending down, and finally breaking off, the natural crust of 

 the surface. The necessity therefore follows, under those circumstances, of employ- 

 ing an excess of earth in forcing out laterally, and forcing down vertically, the running 

 sand or soft puddle cf the underlying foundation in order to compress those soft materials 



