Pollutant Spreading in a Small Stream: A Case Study in Mala Nitra Canal in Slovakia

Abstract

The Water Framework Directive requires as an obligatory goal to achieve and to keep "good water quality" status within the defined period (for Slovakia-up to the year 2015). For surface waters, the main criterion is the ecological and chemical status of the water. Mathematical and numerical modelling allows evaluating various situations of contaminants spreading in rivers (from everyday wastewater disposal through fatal accidents and discharges of the toxic substances) without immediate destructive impact to the environment. Determination of longitudinal and transverse dispersion coefficient values, as the main hydrodynamic characteristics of the dispersion, has the highest extent of uncertainty for hydrodynamic models simulating pollutant transport in streams. This paper deals with the determination of dispersion coefficients based on field tracer experiments performed in a small modified stream (basic hydrodynamic parameters during the experiments were: discharge Q = 0.138-0.553 m 3 .s −1 , depth h=0.29-0.48 m, width B=5.2-5.9 m). During the experiments, various conditions and situations were taken into account, e.g., continuous and instantaneous pollution source, as well as various positions of pollution source along the river width, among others. Field measurements were evaluated using three different methods for dispersion coefficient determination: based on statistical evaluation, based on analytical solutions of advection-dispersion equation, and using numerical models. The dimensionless dispersion coefficients values were determined, which can be used for numerical simulation of pollutant transport in similar types of streams.

Evaluating longitudinal dispersion of scalars in rural channels of agro-urban environments

“…The calibration involved both D and U, as often done in the literature [see e.g. 3,92,40], and the best fit between the experimental data and the analytical solution was obtained through a least squares minimization.…”

“…The difficulties associated with the determination of D represent one of the highest sources of uncertainty for hydrodynamic models simulating pollutant transport in streams. Hence, the recommended practice is to carry out field measurements to directly quantify D and then use the gained information to select the most reliable formula among the existing ones or to build a new site-specific formula [4,48,73,92].…”

Estimation of river Tigris dispersivities using a steady-state numerical model

“…The main flaw of the 1D model is that they are not capable of simulating the pollution spreading until the mixing of pollutants across the stream section becomes complete (Velísková et al 2014). Two-dimensional (2D) model seems valid, and therefore, a 2D model was chosen in this study since they can adequately describe the modeled system.…”

“…Moreover, the estimated dispersion coefficients through a tracer experiment are valid for only the examined stream segment (Abderrezzak et al 2015). Consequently, numerous studies were conducted to develop empirical formulas for the determination of both the longitudinal and transverse dispersion coefficients (Fischer 1967 Seo and Cheong 1998;Baek and Seo 2013), or sometimes the coefficients are achieved by researcher's own experience (Velísková et al 2014). Detailed and brief reviews and comparison of these empirical formulas can be found in Seo and Cheong (1998) and Baek and Seo (2016).…”

Longitudinal Dispersion Prediction of River Balogun Using Constant Distance and Time Approach at Different Sampling Time Intervals

“…However, when this is hampered, their existence will be under threat. With the EU bearing this in mind, a Water Framework Directive (WFD) in 2000 was designed to help chart this course [1], [2]. Even at that, it is herculean to find some of the rivers within the EU member states void of some form of effluent discharge.…”