AN APPROXIMATE SOLUTION TO THE CONVECTION-DISPERSION EQUATION OF SOLUTE TRANSPORT IN SOIL

This paper uses a boundary-layer method to solve the convection-disper sion equation (CDE) to predict solute transport in soil. The boundary- layer solution describing chemical transport for a semi-infinite soil column or field soil profile has the advantages over the corresponding exact solution of simplicity in expression and flexibility in manipul ation. Comparisons of the boundary-layer solution to the exact solutio n are conducted for a range of parameter values. Results show that the boundary layer solution is in good agreement with the exact solution. An important application of the boundary-layer solution is the estima tion of transport parameters of solute movement through soils under bo th laboratory and field conditions. This leads to a new method for est imating parameters of solute transport in soils. The new method requir es observation of the advance of the depth of boundary layer (solute f ront) with time. This can be done visually by using a tracer solution with dye in it. The new method is simple, saves time, and is applicabl e to both laboratory soil columns and field soils.