Modelling of water infiltration into water repellent soils

Abstract

Abstract. Infiltration into water repellent soils has been widely observed, quantified and documented. The modelling of water infiltration into water repellent soils is more rarely taken into account explicitly. In this study, we modelled water infiltration into water repellent soils considering explicitly the contact angle, with the geometrical pore model proposed and validated previously. The applied microscopical approach showed good agreement with macroscopical models and with experimental data. We firstly investigated the case of contact angles lower than 90°, for the cylindrical pore and pearl necklace (PN) models. The cumulative infiltrations were numerically generated versus contact angle and for different pore radii. Then, the modelled infiltration curves were fitted to the two-terms Philip equation and parameters S and A were evaluated versus contact angle. As predicted sorptivity S decreased with increasing contact angle, and the constant infiltration rate A increased with contact angle for both models. Then, the modelled data were fitted to the numerical solution of the Richards equation to derive the equivalent hydraulic parameters assuming van Genuchten model. The results showed that the contact angle decreased the saturated hydraulic conductivity and increased the parameter α. Lastly, our model was used to investigate strong water repellency with contact angles higher than 90°. Cumulative infiltration and related Philip parameters, S and A, were evaluated versus water pressure head at surface h0 and contact angles (between 90° and 96°). Our model may be used to predict water infiltration into water repellent soils for both moderate and strong water repellency, including fingering features