Design of Tile Drainage for Falling Water Tables

by Jan van Schilfgaarde,


Serial Information: Journal of the Irrigation and Drainage Division, 1963, Vol. 89, Issue 2, Pg. 1-12


Document Type: Journal Paper

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Abstract: An equation is derived for the spacing of the drains in terms of the rate of water-table drop, the depth of an impervious layer below the drains, the hydraulic conductivity of the soil, and an assumed constant drainable pore space. The solution is based on the Dupuit-Forchheimer assumptions. It treats the depth of the water-bearing stratum as a variable, so that it is not restricted to cases in which the water-table fluctuation is a small percentage of the aquifer thickness. To account for the convergence of flow toward the drains when drain spacing is not large relative to aquifer depth, the use of a graphical correction is proposed, adapted from a tabulation of equivalent depths by Hooghoudt. The solution is in terms of an incomplete beta function which can either be evaluated numerically from a simple graph or determined within 3% from an approximate equation. A comparison with an earlier, widely used, solution by Glover illustrates the significance of the improvements.

Subject Headings: Drainage | Water table | Spacing | Aquifers | Hydraulic conductivity | Thickness | Convergence (mathematics) | Flow visualization

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