UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 854 
Contribution from the Bureau of Public Roads 
THOS. H. MACDONALD, Cliief 
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, Professor of Mechanics and Hydraulics 
State University of Iowa 
CONTENTS 
Page 
Introduction 1 
Scope of the Investigation 2 
Conclusions 4 
Description of Experimental Plant ... 6 
Pumping Plant ; 6 
Supply Tanks 5 
Weirs 6 
Hook Gages . 6 
Flume 8 
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 
Page 
Necessary Data for Comparing Velocity 
FormulsB 12 
Mean Velocity 12 
Hydraulic Grade or Slope .... 12 
Interna! 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 Flowing Full ... 35 
Formulae for TCe Flowing Partly Full 40 
Comparison of Various Formulae ... 47 
Loss of Head in Catch-Basins .... 49 
WASHINGTON 
GOVERNMENT PRINTING OiTICB 
1920 
