Analysis of Saturation Risk in Sprinkler Irrigation: Case of Cherfech Irrigation Perimeter in Tunisia

This study is targeted to the assessment of the saturation risk in sprinkler irrigation. For this purpose, in situ field trials were carried out to infer the saturated hydraulic conductivity (Ks) and sorptivity (S) using the disc infiltrometer method. Since the measured values of Ks are very close to prescribed application rate, caution is required. In a first step, the pressure head at the wetting front (hf) and the useful porosity (θs – θi) are assumed to be constant. Thus, the logarithmic derivation of the sorptivity provides a relation between relative variations of S and Ks. The ponding time (Ts) is estimated from Green and Ampt (1911) and Philip (1957b) infiltration equations. The risk of saturation is deemed to be inexistent inasmuch as simulated values of Ts are greater than the irrigation times practiced in the zone. In a second step, the values of the pressure head at the wetting front and saturated water content were assumed to be variable with soil texture. Simulations of the ponding time were carried out based on Rawls and al. (1981) data. For the recommended sprinkler spacing in the Cherfech perimeter (12 m × 12 m), the simulations show a good agreement between Ts values generated from Green and Ampt and Philip equations for Ks ranging from 1.5 to 6 mm/h. Moreover, it was established that saturation risk due to a gradual texture variation is virtually inexistent in the conditions prevailing in Cherfech perimeter.