FLOW OF WATER THROUGH PIPES. I4I 



as collected by a series of laterals and brought by them 

 to various points along its course. The same is true 

 of many drains which are laid into ponds. The pond 

 collects surface water from a considerable area, and 

 none of it can enter the drain until it reaches the center 

 of the pond. 



In such cases and many similar ones which occur 

 in practice, the acreage should be converted to its 

 equivalent of tile-drained land before the formula is ap- 

 plied for the purpose of determining the size of drain 

 which should be used. Find the area of the land which 

 has a surface slope in the direction of the drain, and 

 which is not tiled, add one half to the area if in gen- 

 eral it has a slope of 2 or 3 to 100, and apply the 

 formula to the corrected acreage. If the slope is 

 steeper, the acreage should be increased proportion- 

 ally. For example, a pond through which a drain 

 passes may have a water-shed of six acres, but may slope 

 toward the center at the rate of 2 or 3 per 100. The 

 drain should not be proportioned for six acres, but for 

 one half more, or nine acres. Mains are not propor- 

 tioned according to the number of lines of tile which are 

 to discharge into them, but according to the area of 

 land from which they must take the drainage. 



Limitations of Size, Grade, and Length of Drain. 



From what has preceded, it will have doubtless oc- 

 curred to the reader that there are certain limitations 

 to the size of the drain used, its grade, and the total 

 length of the line, beyond which it is not wise to go. 

 In formula No. 2 the denominator of the second num- 

 ber represents the resistances which oppose gravity. 



