Abstract

ZAVALA, Manuel; SAUCEDO, Heber  and  FUENTES, Carlos. Fractal radiation model for agricultural drainage based on the Richards and Boussinesq equations. Tecnol. cienc. agua [online]. 2011, vol.2, n.3, pp.141-157. ISSN 2007-2422.

The movement of water in an agricultural subsurface drainage system is analyzed using a model based on the coupling of the Richards equation and the Boussinesq equation, with variable storage capacity subject to the drain fractal boundary radiation condition. The model is used to describe the hydraulic operation of a drainage system installed in the field, which allows for studying drain separations of 40 m and 25 m. Most of the hydraulic characterization of the system is conducted independently of drainage tests using a methodology based on the granulometric curve and total porosity of the soil. The experimental evolutions of the drained depth and the decrease in the hydraulic head associated with a 40 m separation between drains allow for calibrating two parameters of the proposed model: the pressure scale related to the soil-water retention curve and the scale parameter of the fractal radiation. The experimental evidence corresponding to a 25 m separation between drains enables showing that the scale parameter of fractal radiation is independent of the drain separation, and that it can be assumed to be proportional to the saturated hydraulic conductivity of the soil. It is shown that the classical hypotheses regarding agricultural drainage represent, in a simplified manner, the transfers developed in the partially-saturated zone, considering the recharge term in the Boussinesq equation to be null and or equal to the evapotranspiration rate; transferring uncertainty about what happens in the zone to the parameters estimated based on drainage tests.

Keywords : vadose zone; saturated zone; shallow unconfined aquifer; recharge; discharge.

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