Solute transport in streams with diffusive transfer in the hyporheic
zone is studied. Analytical solution of the diffusive transfer model is
obtained by means of Laplace transform. Solutions are derived for a general
situation, in which the concentration at the injection point is a function
of time. In order to illustrate the use of present analytical solution,
physical transport parameters are estimated for the observed data of Uvas
Creek tracer experiment for chloride concentration and also of Wkra river
tracer experiment. The concentration-time breakthrough curves obtained from
the analytical solutions are found to be in good agreement with the
observed as well as numerical concentration-time breakthrough curve. Step
concentration-time profile and continuous concentration-time profile are
considered as upstream boundary conditions for conservative solute. An
instantaneous injection of solute is taken as an upstream boundary
condition for reactive solute. It is noticed that with the increase in the
value of porosity, the solute concentration in the main channel decreases.
With the decrease in the value of Peclet number in the hyporheic zone, the
overall solute concentration in the main channel decreases. Due to increase
in the value of the sorption rate coefficient in the hyporheic zone, solute
particles once enter into the hyporheic zone, reside for a longer time in
the hyporheic zone. A sensitivity analysis is performed in order to
identify the critical parameters for conservative as well as for reactive
solute. It is found that the ratio of cross-sectional areas is much more
sensitive compared to the other parameters for conservative solute. The
Damkohler number in the hyporheic zone is the most sensitive parameter
among all the parameters for reactive solute. The above observations
indicate that the analytical solution can be reliably applied for the
analysis of tracer experiments.
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