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Tile Drainage in Bedded Soil or a Draw¹

ABSTRACT

The process of shaping flat land by plowing it into a series of ridges separated by parallel dead furrow is called bedding and the ridge-furrow systems are called beds. The furrows are supposed to remove surface water from the ridges, but often do not. In this paper the amount of water that can be removed by tile if they are placed under the furrows is computed on the basis of Darcy's law and potential theory. In the analysis, water-saturated, steady-state conditions and a subsurface barrier on which the drain tile are laid are assumed. For a poorly drained prairie soil, the calculations show that tile (or plastic tubes, etc.) placed 0.35 m below the furrow bottoms and 30 m apart in beds of 2% slope will remove 5 mm of water/day, and that the bed furrows would have to remove an additional 4.52 mm/day to take care of an expected drainage coefficient of 9.52 mm/day. For general use, 28 depth and spacing geometries are analyzed and tabulated for amounts of flow to tile in the beds. For certain geometries, some of the recharge rainfall seeps in and out of the ridge slope before the water seeps down again into the soil. This in and out seepage occurs for small tile depths, and small tile sizes. Flow nets are presented. It is shown that the theory applies to the drainage of a draw.

¹ Journal Paper No. J-7823 of the Iowa Agric. and Home Econ. Exp. Stn., Ames. Project no. 1888 and 2058. Supported in part by the Office of Water Res. and Technol., U.S. Dep. of the Interior, through Project A-044-IA of the Iowa State Water Resour. Res. Inst. and the National Science Foundation Grant no. Eng. 75-19394.

² Formerly Research Associate in Agronomy, Iowa State Univ., Ames, now Assistant Professor of Agronomy, Virginia Polytech. Inst. and State Univ., Blacksburg, and Professor of Agronomy and Physics, Iowa State Univ., Ames, respectively.

Received for publication March 17, 1975. Accepted for publication May 19, 1976.