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11.3

The discharge of a river with a cross-sectional area of 10 m^2 is 2m^3*s^-1. At a time t=0 a dye tracer is released into the river. Calculate the time needed for the tracer to reach a measurement location 500 downstream from the release point, assuming that the tracer is subject only to advection.

11.5

A flow reactor with a cross-sectional of 16 m^3 s^-1 and a sodium concentration area of 0.8 m^2 is filled with sandy sediment with a dispersivity α of 0.01 m. The sediment is fully saturated with water with concentration of 250 mg I^-1. At a time t=0 a continuous inflow of water with a Cl concentration of 250 mg I^-1 is started with a flow velocity of 1 m d^-1 .

a- Calculate the dispersion coefficient

b- Does this coefficient refer to longitudinal or to transverse dispersion? Give reasons for your answer.

c- Calculate the Cl concentration at x= 1.0 m after 18 hours, using equation (11.32)

d- Calculate the Cl concentration at X=1.0 m after 36 hours.

e- Compare the answers of questions C and D and explain the outcomes

Equation for (11.32) that needs to be used is the following: