Calculation of non-steady flow towards a drain in saturated-unsaturated soil by finite elements

Zaradny, H.; Feddes, R.A.

doi:10.1016/0378-3774(79)90012-x

Cited by 24 publications

(12 citation statements)

References 6 publications

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“…This is especially significant for soils which exhibit pronounced changes in water content and hydraulic conductivity, even for small differences in pressure head h (see, e.g. Zaradny & Feddes, 1979;Zaradny, 1993).This also highlights the fact that a numerical solution should always be verified against seepage theory and/or known solutions if they are available. A good computer program does not guarantee that the computed results will be accurate, and should therefore be actively checked against the principles of soil water physics.…”

Section: Discussionmentioning

confidence: 99%

“…A general rule observed in the computations of Zaradny & Feddes (1979), was the application of smaller elements at locations where the gradients were high or very variable, and where more detailed information was sought.…”

Section: Solution Of the Richards Equationmentioning

confidence: 99%

“…Due to the nonuniform flow region having irregular boundaries and arbitrary degrees of local anisotropy, as well as the potential type of boundary conditions (e.g. the atmospheric boundary conditions), finite element models (FEM) are preferable (Zaradny & Feddes, 1979;Zaradny, 1993).…”

Section: Solution Of the Richards Equationmentioning

confidence: 99%

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Remarks upon numerical solutions of infiltration into a soil profile

Zaradny

2009

Hydrological Sciences Journal

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A methodology of time-step estimation for numerically solving the Richards equation is discussed. Its importance in simulating water movement in unsaturated-saturated soils is shown for infiltration into a soil profile by applying various time-step estimations and boundary conditions for different soils. In order to test the results of the computations, infiltration theory was applied. According to infiltration theory, the pressure head in the initially unsaturated part will not take positive values as long as the moisture front has not reached the phreatic level, or, in the case of a profile with a free-draining lower boundary, it is not saturated at the base. In other cases, the appearance of positive values of the pressure head produces incorrect values for the inflow rate q.Key words water movement; unsaturated-saturated soil; infiltration; Richards equation; numerical solution Remarques sur la résolution numérique de l'équation d'infiltration dans un profil de solRésumé Une méthodologie d'estimation du pas de temps dans la résolution numérique de l'équation de Richards est discutée. L'importance de cette question pour la simulation des mouvements d'eau dans des sols non saturés-saturés est mise en évidence pour l'infiltration dans un profil de sol, en appliquant différentes estimations du pas de temps et différentes conditions aux limites pour plusieurs sols. La théorie de l'infiltration est appliquée pour tester les résultats des simulations. D'après cette théorie, la hauteur piézomérique dans la partie initialement non saturée ne prend pas de valeurs positives tant que le front d'humidité n'a pas atteint le niveau phréatique ou que, dans le cas d'un profil présentant une limite inférieure librement drainante, la base n'est pas saturée. Dans les autres cas, l'apparition de valeurs positives de la hauteur piézométrique entraîne des valeurs incorrectes pour le flux d'infiltration q.

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Section: Discussionmentioning

confidence: 99%

Section: Solution Of the Richards Equationmentioning

confidence: 99%

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Remarks upon numerical solutions of infiltration into a soil profile

Zaradny

2009

Hydrological Sciences Journal

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“…As a practical matter, the analysis of agricultural drainage is made either with the Richards equation (Zaradny & Feddes, 1979;Fipps & Skaags, 1986;Saucedo et al 2002) or else with the Boussinesq equation of agriculture drainage (Dumm, 1954;Pandey, et al, 1992;Gupta et al, 1994;Samani et al, 2007). The Richards equation allows the executing of descriptions of the transfer processes occurring in the saturated and unsaturated zones of the soil; however, its application to the scale of an irrigation district and even that of the a farm field, is limited due to the difficulty and cost of the experim e n t a l w o r k r e q u i r e d t o d e p i c t t h e s o i l ' s hydrodynamic characteristics (the moisture retention curve and the hydraulic conductivity curve) as well as the necessary effort of calculating a three-dimensional water movement in the soil.…”

Section: Macroscopic Scalementioning

confidence: 99%

Comparison of Two Nonlinear Radiation Models for Agricultural Subsurface Drainage

Zavala¹,

Saucedo²,

Bautista³

et al. 2012

Drainage Systems

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“…Neuman (1973) solved the same type of problem considering the contribution of the flow in the unsaturated zone. The application of the same numerical approach solution to subsurface drainage by drain pipes is described in Zaradny and Feddes (1979).The method suffered further improvements to allow it to represent drains in the numerical mesh (Tarboton and Wallender 2000) and also suffered further numerical refinements to diminish the loss of mass and the numerical oscillation in the computation (Pan et al 1996).…”

Section: Introductionmentioning

confidence: 99%

A simple numerical analyses software for predicting water table height in subsurface drainage

Castanheira

Santos

2009

Irrig Drainage Syst

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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.

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Calculation of non-steady flow towards a drain in saturated-unsaturated soil by finite elements

Cited by 24 publications

References 6 publications

Remarks upon numerical solutions of infiltration into a soil profile

Remarks upon numerical solutions of infiltration into a soil profile

Comparison of Two Nonlinear Radiation Models for Agricultural Subsurface Drainage

A simple numerical analyses software for predicting water table height in subsurface drainage

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