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Empty Drain and the Water Level at Midway between the Drains. Aspects Regarding Management

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  9th International Drainage Symposium held jointly with CIGR and CSBE/SCGAB Proceedings, 13-16 June 2010  IDS-CSBE-101372.(doi:10.13031/2013.32180)
Authors:   Paulo Jorge Castanheira
Keywords:   Drainage, Controlled Drainage, Numerical Simulation

Standing water above drains as a result of a submerged drain outlet, promotes flow conditions so that there is a smaller rise in the water table height at midway between the drains. This case has been studied through theoretical analyses by van Deemter (1950); Childs (1958), Kirkham(1958); Santos-Jnior (1971); Wessseling (1979) an Gammal et al (1995). In this paper the numerical results from DRENAFEM software package simulator are compared with the theoretical analysis of Santos-Jnior (1971). The software uses a finite element analysis to solve the Richards equation. Several simulations were performed with a small drain radius, and with a back pressure in the drain outlet to achieve a high entrance resistance and promote the rise of the water table at midway between the drains. With the standing water above the drains, the theoretical and numerical results show a rise in the water table height which is smaller than the drain outlet pressure. This paper demonstrates how the software can be used to simulate the behavior of a water table under controlled drainage to determine the water tables position in situations with no analytical solutions, such as hydraulic conductivity anisotropy or in non-homogeneous soils with several layers.

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