Model of border irrigation runoff, advance and infiltration on a soil covering a very permeable subsoil

Developed in an MS Excel spreadsheet, Calhy is a one-dimensional model of border irrigation on a uniform plot for a soil underlain by a well draining layer. With the kinetic or diffuse wave assumption, it fits the Green and Ampt model and the Manning-Strickler equation, taking into account surface retention. With five parameters, two of which are measured and describe the initial soil moisture and three are optimized, the model reproduces the advance and outflow observed during several irrigations on a grassland in the semi-arid Crau plain (southern France). The optimized parameters are: hydraulic conductivity of soil at saturation, constant over time; the Strickler coefficient and the surface storage, decreasing during the season probably due to the development of flora and the microrelief. Being didactic and user friendly, the model can help to optimize irrigation, with the aim of obtaining the desired infiltration by providing as little water as possible.