THE FLOW OF WATER IN DRAIN TILE. 6 



reported, however, deals only with the discharge or carrying capacity 

 of tile drains as conduits. No tests were made on sizes smaller than 

 4 inches in inside diameter, as the use of smaller sizes now is con- 

 sidered generally inadvisable, the small bore greatly increasing the 

 danger of obstruction by sediment or by displacement. 



Laboratory methods are essential for securing definite results 

 in such an investigation, in order that each factor influencing the 

 flow may be varied through a considerable range, yet always subject 

 to control, while the other factors are maintained constant. Only 

 in this manner can each influence be measured separately. The 

 factors influencing the velocity of flow in a tile drain are: the inside 

 diameter of the pipe, the depth of the water flowing, the slope or 

 grade of the water surface (which ordinarily is that of the tile line), 

 and the roughness and irregularity of the interior surface and of 

 the joints. On tile lines installed for actual use in land drainage 

 the grade of each line is fixed; most of the time they are empty or 

 carry but little water; the amount of flow depends upon weather 

 and seasons and can not be regulated for investigation; and when 

 the flow is considerable the weather is likely to be bad, the roads 

 practically impassable, and the ground surface covered with water — 

 conditions that make it impossible to secure satisfactorily precise 

 measurements in tile several feet under ground. 



The principal feature of the equipment for making the experiments 

 was a wooden flume about 570 feet long, in which the tile were laid 

 in earth exactly as drains are installed in the ground. The flume 

 was adjustable to any grade up to 1.50 per cent (s= 0.015), without 

 disturbing the tile. The depths of flow were observed by piezometer 

 tubes hung on the side of the flume. Care was taken to make the 

 tile lines truly representative of drains ordinarily well laid under field 

 conditions. 



Experiments were made with all the usual commercial sizes of tile, 

 both of clay and of concrete, from 4 to 12 inches inside diameter. 

 Nine grades were used, from 0:05 to 1.50 per cent, for each size and 

 kind of tile. For each size, kind, and grade it was desired to test 

 depths of flow of one-fourth, three-eighths, and one-half the internal 

 diameter of the tile, and other depths ranging from half full to full 

 by successive increases of 5 per cent of the diameter. However, 

 because of the practical difficulty of securing exactly any given depth 

 of flow, the number of tests was considerably less than anticipated 

 in the smaller sizes of tile. Also, the capacity of the pumping plant 

 was not sufficient to fill the largest tile at the maximum grade. 

 Tests were run, also, with the tile under slight internal pressure. 

 In all, 824 separate tests were made, and from these a new formula 

 has been devised for computing the flow in drain tile. 



