FIFTH ANNUAL YEAR BOOK — PART VI. 525 



permitted, well known authorities could be quoted to prove that clay soils 

 have been drained with a full measure of success. But we must be content 

 to briefly call attention to one or two important points in this connection. 



On very heavy clay lands the tile should not be placed too deep, for the 

 water will not reach it as rapidly as desired. Wherever the water has great 

 difficulty in getting to the tiles because of the tenacity of the soil, and there 

 is little danger of silt getting into the tiles, it is a most excellent practice to 

 cover them with a few inches of small stones and gravel. These materially 

 assist the water in reaching the drain quickly. If the materials named are 

 not readily available, brush, straw or corncobs may be used. A few years 

 ago an Illinois farmer uncovered a number of tile drains which were located 

 in a stiff timber soil. These drains had not discharged any water for several 

 months previous to the time they were uncovered. Corncobs and other 

 coarse material were placed in the newly opened ditches and thereafter the 

 drains discharged freely and greatly improved the tract in which they were 

 located. 



Underdrains placed in a stiff clay are more effective the second year than 

 the first and their efficiency usually increases steadily for several years. It 

 is not difficult to understand the reason for this marked improvement. All 

 soils, and especially clays, expand when wet and contract when dry. There- 

 fore, when a clay soil is tile drained, that soil which is freed of a portion of 

 its water becomes dryer than the rest. Then shrinkage cracks are formed 

 in this clay; these cracks extend outward and become longer and longer as 

 the drained and dried areas increase in extent. Naturally these shrinkage 

 cracks serve as drains or openings through which the soil water readily finds 

 its way to the drains. After the lapse of a short time small fissures extend 

 out from the main channels and thus the entire soil mass is divided into 

 small blocks or portions and thereafter this clay which at first was tenacious 

 and impervious to water, or nearly so, presents the most favorable conditions 

 for the ready movement of air and water within its depths. And, again, 

 the roots of plants, such as clovers, deeply penetrate the drained clay soils 

 and when they decay, numerous passageways are left in the soil through 

 which the water readily finds its way to the drains. Thus it is that in a few 

 years after drains have been installed, a stiff clay soil is rendered open and 

 porous and well adapted to the production of crops. 



The resistance to the flow of water increases as the soil texture becomes 

 more close. Hence the more open the soil the farther apart the drains may 

 be placed. In loose, loamy soils, and particularly those underlaid by sand, 

 good drainage is often secured with drains one hundred feet apart and 

 sometimes the distance is even greater. Clay is the finest grained soil we 

 have and therefore in this soil drains must be placed quite near each other. 

 Unfortunately, experiments which might aid the engineer on this point, 

 havenot yet been carried on. The demand for data relating to this problem is 

 increasing constantly. We trust that in the near future this problem will re- 

 ceive attention from investigators which it merits by reason of its importance. 

 Drainage is an improvement which is too important and expensive to permit 

 of careless and haphazard work. Whenever drains are located too far apart, 

 failure to accomplish the end in view inevitably results. When they are 

 placed too near there is loss of time and money. It is true that so many 

 local conditions affect the distance apart at which drains should be placed 



