Treatment of Stagnant Zones in Riverine Advection-Dispersion

Advection-dispersion in streams encounters pockets of stagnant or dead zones in the flow, which trap the injected tracer. Treatment of stagnant or dead zones for dispersion is presented using one-dimensional advection-dispersion equation. A method is suggested for simultaneous estimation of dispersion coefficient, apparent (or effective) velocity, and effective injected mass of tracer, from a temporal concentration profile observed at a downstream section. The method is robust and uses a nonlinear optimization. Using the method procedure for estimation of adsorption coefficient for riverine advection-dispersion has also been suggested. The effective velocity is related to the stagnant zone fraction (average fraction of cross-sectional area attributed to stagnant zones) and adsorption. The application of the method on published data sets show that the parameter-estimates are reliable and the observed concentration profiles are closely reproduced. The analytical procedure described for the treatment of stagnant zones may have a wide application in civil engineering as well as other fields. The amount of chemicals released from the industrial units or by an accident can be estimated.