UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 854 



Contribution from the Bureau of Public Roads 

 THOS. H. MACDONALD, Chief 



S&T'&J-U 



Washington, D. C. 



PROFESSIONAL PAPER 



August 26, 1920 



THE FLOW OF WATER IN DRAIN TILE. 



By D. L. Yarnell, Senior Drainage Engineer, and Sherman M. Woodward, Pro- 

 fessor of Mechanics and Hydraulics, State University of Iowa. 



CONTENTS. 



Introduction 1 



Scope of the investigation 2 



Conclusions 4 



Description of experimental plant 5 



Pumping plant 5 



Supply tank 5 



Weirs 6 



Hook gages 6 



Flume 6 



Method of changing grade 6 



Laying the tile 7 



Covering the tile 7 



Piezometers and piezometer tubes 8 



Nomenclature ■ 9 



Formulae for flow of water in drain tile 9 



Necessary data for comparing velocity for- 

 mulas 12 



Mean velocity 12 



Hydraulic grade or slope 12 



Internal size of drain tile 13 



Actual depth of flow 14 



Methods of conducting tests 15 



Measurement of mean velocity 17 



Results of observations 18 



Discussion of computations 34 



Formulas for tile flowing full 35 



Formulae for tile flowing partly full 40 



Comparison of various formulae 47 



Loss of head in catch-basins 49 



INTRODUCTION. 



The discharging capacity of tile drains has become a matter of 

 considerable importance in recent years, on account of the heavy 

 investments being made in this kind of agricultural improvement. 

 Drain tile in small sizes have been used for a long time, but recently 

 much larger sizes, 2 feet and more in diameter, have come into rather 

 common use in some States. Where tile 24 to 48 inches in diameter 

 and larger are to be installed, at a cost of $8,000 and upward per 

 mile, reducing the diameter 2 or 3 inches may mean saving $500 to 

 $1,500 per mile. 



Planning the best tile-drainage system for any situation is a com- 

 plicated problem of balancing many diverse and uncertain factors 

 of benefit and cost. The point of largest rate of return upon the 

 investment can not be determined exactly. Obviously, a point 

 may easily be reached . where additional expenditure, although se- 



166537°— 20— Bull. 854 1 



