UNITED STATES DEPARTMENT OF AGRICULTURE 
J^^^P^u 
BULLETIN No. 854 
Contribution from the Bureau of Public Roads 
THOS. H. MACDONALD, Chief 
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 
riezomerers and piezometer tubes 8 
Nomenclature 9 
Formulae for flow of water in drain tile 9 
Page. 
Necessary data for comparing velocity for- 
mulae 12 
Mean velocity 12 
HydrauKc 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 
Formulae for tile flomng 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 som.e 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- 
166597°— 20— Bull. 854 1 
