Behaviour and prediction of infiltration in layered soils

The behaviour of vertical infiltration in layered soil was studied in soil columns on a sandy loam and a clay loam, having a fine sand layer of varying thickness (0.10, 0.15, 0.20m) situated at 0.15, 0.25, 0.35m depth from soil surface. Irrespective of depth and thickness of impending sand layer, a sharper decrease in infiltration rate was noticed once the waterfront reached the sandy layer. The period of reduced rate was followed by an instantaneous increase and its amplitude was found to be incremental with the thickness of the impending layer. It was also observed that the time taken for peak rise of infiltration rate was longer in heavy soil compared to light soil for similar thickness of sand layer. Cumulative infiltration for all the combinations of layered soil were predicted with the help of predetermined sorptivity and hydraulic conductivity of the sand and surrounding soil using Philip's infiltration model. All the predicted values were similar in nature to measured values with an inflection at a particular point of time depending upon the thickness and depth of sand layers. The evaluation of predictive capacity of the said model with reference to all the soil columns was examined using the scatter plots. The statistics inferred that in sandy loam soil, 0.15m thickness of sand layer situated at 0.35m depth performed the best and in clay loam soil, 0.15m thickness of sand layer situated at 0.15m depth indicated a satisfactory fit in that model among the three depth and thickness.