1. Research Hydraulic Engineer, Cemagref, UR Irrigation 361, Rue J.F. Breton, B.P. 5095, 34033 Montpellier Cedex 1, France. E-mail: xavier.litrico@cemagref.fr
2. Research Control Engineer, INRA, LASB, 2 Place Viala, 34060 Montpellier, France. E-mail: fromion@ensam.inra.fr