Desiccation of shrinkable soils can result in cracking of the ground. The cracks subsequently close on wetting up of the soil. The cracks can increase the mass permeability of a soil by several orders of magnitude. The modelling of crack formation and their closure involving seasonal changes in rainfall and evapotranspiration presents a challenge in boundary value problems where permeability has a significant influence on the accuracy of predictions. This paper presents a smeared permeability model which simulates the variation in permeability during cracking and subsequent wetting up of a soil.