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Laterally Confined Flow From a Point Source at the Surface of an Inhomogeneous Soil Column¹

ABSTRACT

Solution of a linearized flow equation for steady, axisymmetric, laterally confined infiltration from a point source located at the soil surface is compared with pressure head patterns measured in an undisturbed column of sandy loam. The geometry approximates an array of trickle irrigation emitters. The hydraulic conductivity could be represented as an exponential function of both the pressure head and the depth in the column. This implies that steady, multidimensional flow in the column is described by a linear flow equation.

Measured and predicted distributions of pressure head agreed most closely at an application rate of 0.5 cm/day. Increase in the size of a saturated zone about the point source at application rates higher than 0.5 cm/day caused isolines of pressure head to be distorted from the predicted shape. Flow patterns for homogeneous and heterogeneous soil are compared.

Trickle irrigation systems are usually operated intermittently. Measured distributions of pressure heads under intermittent application were compared with steady infiltration patterns. A steady-flow solution will give an approximate prediction of intermittent pressure head patterns for continuously repeated application cycles over part of the flow region and during part of the time.

¹ Contribution from the U. S. Salinity Laboratory, Science and Education Administration, USDA, 4500 Glenwood Dr., Riverside, CA 92501.

² Formerly Physicist and formerly Soil Scientists. Current location of S. D. Merrill is Northern Great Plains Research Center, USDA-SEA, P. O. Box 459, Mandan, ND 58554; current location of P.A.C. Raats is Instituut voor Bodemvruchtbaarheid, Oosterweg 92, Haren (Gr.), The Netherlands; current location of C. Dirksen is Laboratory of Soils and Fertilizers, Agricultural State Univ. Wageningen, The Netherlands.

Received for publication March 6, 1978. Accepted for publication June 26, 1978.