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Depth of Barrier and Water Table Fall in a Tile Drainage Model¹

ABSTRACT

A laboratory model having a transparent photographable front and containing glass beads has been used for determining, under idealized conditions, the influence of a barrier on tile drainage, in regard to both rate of fall of the water table and tile discharge. Photographs of the modeled water table and the measured discharge as it varies with time are raw experimental data, and charts of dimensionless drainage parameters have been derived therefrom. The results show that changes in depth of a shallow porous medium markedly influence drainage. A critical depth occurs when the barrier is at a depth equal to one fifth of the drain spacing; then the barrier has negligible influence on rate of fall of the water table and on drain discharge. When steady rainfall (in the form of drops of glycerol) was applied, the water table arch at equilibrium was more curved for the higher rates of rainfall. Graphs of rainfall-intensity versus water table height were straight lines both for a position over the tiles and midway between tiles. The data reported here differ from other published data in that here a number of steady state rainfall conditions were used to establish initial conditions. Data were compared with theoretical work, and a good agreement was obtained.

¹ Journal Paper no. J-5254 of the Iowa Agr. & Home Econ. Exp. Sta., Ames, Project no. 998, Department of Agronomy. Work supported in part by Public Health Research Grant No. HEW-WP-00072-04, The US Department of Health, Education and Welfare. Presented before Div. S-1, Soil Science Society of America, Nov. 19, 1964, Kansas City, Mo.

Received for publication November 18, 1965. Accepted for publication March 10, 1966.