190 



LAND DRAINAGE 



subsoil. Proper drainage produces a more pervious con- 

 dition of both soil and subsoil, which eventually, usually 

 shortly, results in the immediate removal of all surplus 

 water (Fig. 79). 



FIG. 80. To illustrate the first conditions described in paragraph 251. 

 S.I, a clay soil. If the area be not too wide, a tile laid at T, the center 

 of the area and at right angles to the slope, will remove the water. 



251. Limited flat or depressed areas on slopes. 

 Two cases are illustrated by Figs. 80 and 81. In the first 

 the soil is a heavy clay or till. In the second example 

 the soil, a sand or loam, is underlaid by a heavy clay or 

 till, which, partly because of its imperviousness, and 



FIG. 81. To illustrate the second condition mentioned in paragraph 251. 

 S is an ordinary soil underlaid by /, an imperVious or semi-pervious 

 layer. The actual condition might vary considerably from that 

 shown in the cut, but the general results would be the same. If 

 the area be not too wide, a tile laid at T, under the foot of the upper 

 slope and at right angles to it, will take care of the water. 



partly because of its saucer-like shape, holds the water, 

 and thus renders the soil above unproductive. In the 

 first case, the water is held upon the surface until it has 

 slowly disappeared, partly down through the soil, and 

 partly by evaporation. In the second case, the water is 



