A two dimensional saturated-unsaturated Galerkin finite element numerical model was used to predict water table height between parallel drains. A user-friendly software (DRENAFEM) was developed to allow for the calculation of the distance between drains and the water table height at middle space between drains. It also allows for determination of variations of the total head throughout the entire geometric space considered in the model. Such facts lead to the design of flow nets with streams lines and equipotentials. The numerical drain outflow is also obtained by using the radial flow equation, conservation of mass and finite element analysis. The results obtained with the model agree well with Khirkam's and Hooghoudt analytical solution for the distribution of total head in ideal drains and for the total head calculations midway between drains.
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-Júnior (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-Júnior (1971). The software uses a finite element analysis to solve the Richard´s 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 table's position in situations with no analytical solutions, such as hydraulic conductivity anisotropy or in non-homogeneous soils with several layers.
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