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Sensitivity of optimized transient storage model parameters to spatial and temporal resolution

Wallis Steve, Manson Russell

Acta Geophysica

2019

Vol. 67, no. 3

951--960

The transient storage model is a popular tool for modelling solute transport along rivers. Its use requires values for the velocity and shear flow dispersion coefficient in the main channel of the river together with two exchange rates between the main channel and transient storage zones, which surround the main channel. Currently, there is insufficient knowledge to enable these parameters to be predicted from the type of hydraulic variables that may typically be available. Hence, recourse is made to tracer experiments, which provide temporal solute concentration profiles that can be used to estimate the parameters by optimizing model output to observations. The paper explores the sensitivity of such parameters to the spatial and temporal resolutions used in the optimization of the model. Data from 25 tracer experiments covering a river flow rate range of 300–2250 L/s in a single reach of the river Brock in north-west England were used. The shear flow dispersion coefficient was found to be the most sensitive parameter; the velocity was found to be the least sensitive parameter. When averaged over all the experiments, mean percentage differences in parameter values between a coarse resolution case and a fine resolution case were of the order of 2% for the velocity, 70% for the shear flow dispersion coefficient and 30% and 20% for the two exchange rates. Since the shear flow dispersion coefficient was found to be small, both in numerical terms and in comparison with an estimate of the total dispersion in the reach, it is suggested that it may be viable to omit the shear flow dispersion term from the model.

Analysis of solute transport in rivers with transient storage and lateral inflow: An analytical study

Kumar A., Dalal D.C.

Acta Geophysica

2010

Vol. 58, no. 6

1094-1114

Solute transport in rivers with transient storage and lateral inflow has been studied by Transient Storage Model (TSM). Analytical solution of the TSM is obtained by means of Laplace transform. In order to illustrate the use of present analytical solution, physical transport parameters are estimated for the observational data of Uvas Creek tracer experiment. Analytical concentration-time breakthrough curves are found to be in good agreement with the observed concentration-time breakthrough curves. A sensitivity analysis has been performed in order to identify the most critical parameter for predicting concentration. It has been found that lateral inflow rate is the most sensitive and the ratio of crosssectional areas is the least sensitive parameter. A hypothetical situation has been considered to study the effects of background concentrations, lateral inflow concentration and its rate. The analytical solutions show that the solute concentration gets diluted or concentrated due to lateral inflow. Physical mechanisms of the problems are well reproduced by the present analytical solutions and these results can be used for analysis of tracer experiments.