Wetting front depth prediction beneath a drip irrigation device
In trickle irrigation, the wetted soil volume fraction (P) is a fundamental parameter for both network design and irrigation scheduling. However, methods used to determine such parameter (P) are still limited and unaccurate. Further, numerical models established for predicting wetted soil volume (or bulb) dimensions remain onerous, complex, expensive, and therefore hardly used. Experimental and numerical results performed on water infiltration from point source on the soil surface show a close relationship between the horizontal and vertical bulb dimensions. This study which was based on continuity and cumulative infiltration equations allowed to establish a new and simple equation for predicting wetted soil depth. This equation enables, knowing initial and wetting front water content and K(hf) (soil hydraulic conductivity on the wetting front), to calculate the front depth Zf(t) beneath a point source with only measuring the front radius Rf(t) on the soil surface. The established equation verifies physical conditions of axisymmetric water infiltration into the soil. The established equation was tested by performing trials on two different soil types and three discharge rates. Two different procedures were simultaneously used for determining Rf(t) and Zf(t). i) observing bulb dimensions evolution on the soil surface and along the symmetry axis. ii) Rf(t) and Zf(t) values were inferred from the horizontal and vertical suction profiles respectively. The Zf(t) values calculated, using such equation, are compared with those measured. The results obtained showed good agreement between calculated and measured data (R2 >=0.94). This study was performed during an axisymmetric water infiltration into bare, homogeneous, and isotropic soil. It needs to be extended to heteregeneous, anisotropic and cultivated soils.