Geoscience Reference
In-Depth Information
Assessing Validity of the Dead Zone Model
to Characterize Transport of Contaminants
in the River Wkra
Magdalena M. Mrokowska and Marzena Osuch
1
Introduction
Application of a model should always be accompanied with the awareness of its
limitations in representing the reality. Besides, it is not only the model alone that is
responsible for the quality of results, but also data used in a calibration process.
In fact, both the errors incorporated in a model and those incorporated in data
affect the model performance. Hence, parameter estimation should be performed
cautiously.
When it comes to environmental models, it is often the case that many sets of
parameters giving equally good predictions exist, which is called equifinality
(Tychonoff and Arsenin
1977
; Beven
2008
). Then deterministic predictions with-
out estimation of associated uncertainty could lead to incorrect results. Hence,
taking into account uncertainty of results is crucial in a calibration process (Blasone
et al.
2008
; Ratto et al.
2001
). In the chapter, an example of deterministic model
calibration combined with assessment of solutions uncertainty is presented.
In this study the one-dimensional dead zone model has been applied. The dead
zone model is an extension of the Fickian model, as it describes not only con-
taminants transport in a main channel, but also incorporates exchange of contami-
nants between the main channel and storage zones (Bencala and Walters
1983
).
The objective of this chapter is to evaluate the validity of the one-dimensional
dead zone model to characterize transport of pollutants basing on a tracer test
performed on the River Wkra. In the chapter, we show that a deterministic solution
to the dead zone model is not unique, as many solutions with acceptable fit to
observations exist. As a result, a model output is associated with the uncertainty. To
assess the uncertainty, and to identify its sources, the sensitivity analysis (SA) and
uncertainty analysis are applied.
