Analysis of Behavior of Contaminants at the Braided River Using the Transient Storage Model

In this study, the behavior of contaminants entering the braided river was analized by using transient storage model (TSM). The TSM equations represent transport and storage processes with a set of numerical variables. The governing equation underlying the model is the one dimensional advection-dispersion equation.

Additional terms such as a first-order decay or production rate terms have been added to consider the non-conservative contaminants condition. This model also includes a sorption mechanism onto the streambed. These additional terms consist of the numerical coefficient part and the concentration difference part. Since the characteristics of decay and sorption are different depending on the type of contaminants, each pollutants have its specific coefficient values. Then, by multiplying this value to the concentration difference term, various kinds of pollutants can be considered.

However, apart from the functions that the model implement, the results of the TSM are greatly influenced by the estimated parameters. In general, calculated parameters from inversely estimated model depends on reach selection. However, there is limited understanding of how to set the reach lengths to reflect the effects of spatially variable hydraulic and geomorphic channel properties. Direct measurements of spatially variable channel properties related to stream hydraulics (e.g., channel depth, width, and velocity) and detailed tracer tests using Rhodamine WT was conducted. Through these experiments, reach lengths with parameters representing each section were calculated.

The test bed, the braided rivers, was simulated with the developed TSM model using the selected number of the reach and reach length. As a result, the accuracy of the model was enhanced compared to the case of using the single reach only. However, the accuracy was not improved greatly than the case of additional term was added.