LEVEES. 85 



than water itself, and must thus, as well as sand, be rejected from the dike. Mould 

 or arable land, though far inferior to clay, is still much better than peat or sand, packs 

 closely, by reason of the smallness of its particles, and is especially suitable for dressing 

 slopes that are to be sodded, as grass grows very well upon it. Clay cannot always 

 be had in a pure state or in sufficient quantities, so that inferior earths must sometimes 

 be mixed with it. But if the precaution be taken to work the best and purest clay on 

 and near the outside, and the inferior sorts in the body of the dike, such sorts may be 

 used without great danger. There are examples of dikes that consist of very sandy 

 soil and have a covering of only one meter of clay on the outer slope, yet they furnish 

 very satisfactory dams. It is easy to be seen, however, that such a dressing of clay 

 must be treated with the utmost care, and the slightest injury to the outer slope must 

 be immediately repaired, for if enough of the clay be removed to permit the water to 

 come in contact with the sand or peat, ve"ry little confidence can be placed in the dike." 



Construction. As has been stated, great importance must be attached to the 

 care with which embankments for water are built. If made simply, as those for rail- 

 roads are constructed, they will be more or less permeable, and when the water comes 

 against them settlement and deformation will result. It is necessary, then, that pre- 

 cautions be taken in cleaning up the foundation and in rolling or tamping the material 

 in place so as to make it compact and close-grained. 



Before beginning the construction of a levee it is important that all vegetable 

 matter, trees, etc., be removed from the site. This should include the roots as well 

 as the trunks and branches. After a thorough cleaning the ground should be plowed 

 or spaded deeply in order to secure a more perfect bond with the new structure, and 

 if the top soil is unsuitable it should be removed before bringing on new earth. Gen- 

 erally the specifications provide for cutting a muck-ditch near the center line of the 

 levee, at the discretion of the engineer. This ditch and all excavations made in remov- 

 ing stumps, trees, etc., are filled up with approved material, well tamped. 



The following clause from Government specifications gives the method of building: 



" The embankment will be started full out to the side-stakes, and be carried regularly 

 up to gross fill, in layers not exceeding 2 feet in thickness, when built by scrapers, and 

 6 inches when built by wheelbarrows. In wheelbarrow work the earth will be care- 

 fully tamped either by wheeling over the embankment or by employing one rammer 

 to two wheelbarrows. When the embankment has been brought up to the proper 

 height, it shall be dressed, and planted with living tufts of Bermuda grass, 4 inches 

 square, and not more than 2 feet apart, well pressed into the earth and lightly covered 

 with soil, to the satisfaction of the engineer in charge, or his designated agent. The 

 contractor will cut down all trees, both great and small, to a distance of 100 feet frotn 

 the base of the levee on both sides. 



" Only clean, unfrozen earth, free from all foreign matter, shall be used in construct- 

 ing the embankment. It will be procured on the river side generally. In no case 

 must it be obtained within 40 feet of the base of the levee on the river side, or within 



