The report deals with the procedures to estimate dispersion coefficient from exit concentration observed due to a step change in the concentration input. A simple method as well as an optimization method has been evolved and the application of the methods on published datasets discussed.
Dispersion occurs in many problems of groundwater flow, such as pollution from concentrated and distributed source, sea water intrusion, seepage of polluted surface water through rivers or lakes and changes in water quality due to artificial recharge. Application of the solution of advection-dispersion equation in soil media for prediction and forecasting of solute concentrations requires the estimate of coefficient of hydrodynamic dispersion, commonly known as ‘dispersion coefficient’.
One of the reliable alternatives for estimation of dispersion coefficient is to conduct a tracer movement test in a soil column and analyze the data for dispersion coefficient. In a tracer movement test, the exit concentration distribution (commonly known as break through curve, BTC) with time is generally observed for known input concentration, often in the form of a step change in concentration input. There is a need to have a simple procedure for quick and reliably accurate estimation of dispersion coefficient making direct use of BTC.
In case when peclet number is low, an optimization method is required for accurate determination of dispersion coefficient. The results indicated that the present methods can estimate dispersion coefficient with reliable accuracy. A computer program in FORTRAN has been developed for the optimization method.
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