In order to study the water flow in the drainage layer of highway under steady-state condition,one-dimensional (1D) Boussinesq equation-based model with Dupuit-Forchheimer assumption was established and the semi-analytical solutions to predict the water-table height were presented.In order to validate the model,a two-dimensional (2D) saturated flow model based on the Laplace equation was applied for the purpose of the model comparison.The water-table elevations predicted by 1D Boussinesq equation-based model and 2D Laplace equation-based model match each other well,which indicates that the horizontal flow in drainage layer is dominated.Also,it validates the 1D Boussinesq equation-based model which can be applied to predict the water-table elevation in drainage layer.Further,the analysis was conducted to examine the effect of infiltration rate,hydraulic conductivity and slope of drainage layer on the water-table elevation.The results show that water-table falls down as the ratio of Is to K decreases and the slope increases.If the aquifer becomes confined by the top of drainage layer due to the larger ratio of Is to K or smaller slope,the solution presented in this work can also be applied to approximate the water-table elevation in unconfined sub-section as well as hydraulic head in the confined sub-section.