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Tile Drainage for Layered Soil¹

ABSTRACT

The effect of a restricting layer (1 foot thick) on the flow of water to drain tiles has been evaluated by the relaxation method using a digital computer to perform the calculation. The following factors were varied alone and in combination: (a) depth to the restricting layer, (b) relative conductivity of the restricting layer to the surrounding soil, and (c) the depth of the drain. For all cases, a constant hydraulic head was assumed along the soil surface and within a gravel envelope surrounding the tile. An impermeable layer was considered to exist at 7 feet.

Drain flux was calculated for each case and compared to give the relative effectiveness of the drains at the selected depths. There is nearly a linear relationship between drain flux and depth of drain when the relative conductivity of the restricting layer to the surrounding soil is 1:10. For 1:100 and 1:1000 conductivity ratio cases, drain flux is nearly independent of depth. The surface intake rate distribution is presented for several cases. The calculations show that a sizeable tension extending over a large portion of the soil profile would be expected for several of the cases.

¹ Technical Paper No. 1303, Oregon Agr. Exp. Sta., Corvallis. Research contribution to Regional Project W-51. Presented before Div. VI, Soil Science Society of America, Nov. 19, 1959, at Cincinnati, Ohio.

² Associate Soil Scientist and Junior Soil Scientist, respectively.

Received for publication April 15, 1960. Accepted for publication June 27, 1960.