International Journal of Scientific Research in Environmental Sciences, 3(5), pp. 0199-0207, 2015 Available online at http://www.ijsrpub.com/ijsres ISSN: 2322-4983; ©2015; Author(s) retain the copyright of this article http://dx.doi.org/10.12983/ijsres-2015-p0199-0207 199 Full Length Research Paper Calculating the Longitudinal Dispersion Coefficient in River, Case Study: Severn River, UK Abbas Parsaie*, Amir Hamzeh Haghiabi Department of Water Engineering, Lorestan University, Khoram Abad, Iran *Corresponding Author: Abbas_Parsaie@yahoo.com Received 02 February 2015; Accepted 07 May 2015 Abstract. Study on the mechanism of Pollutant transmission in the river is a major part of the knowledge of environmental engineering. If the pollution transmission mechanisms in the river with various geometries were specified, the river water quality managing does by more accuracy and his leads to reduce the effects of river pollution on public human's health. In this paper, the pollution longitudinal dispersion coefficient (LDC) is calculated by dispersion routing method for Severn River. To calculate the LDC the concentration profile data published by Atkinson and Davis is used. They considered seven stations along the river for measuring and record the concentration profile at each station. The minimum value of LDC is 12.5 2 1 m s   and maximum value dispersion coefficient is 41.5. 2 1 m s   . For calculating the LDC by empirical formulas, 12 of the famous equations related to the dispersion coefficient is collected and assessing them to calculate the LDC for Severn River shows that the Tavakollizadeh and Kashefipour equation by correlation coefficient about 0.4 is the most accurate empirical formula. Keywords: dispersion routing method; Empirical formula; Longitudinal Dispersion Coefficient, Severn River 1. INTRODUCTION Modeling the pollution transport in rivers included two parts. One- Selecting the Numerical methods with reasonable accuracy, fortunately, recently techniques that have been provided is appropriate). Two- estimating the Longitudinal Dispersion coefficient, the main disadvantage of numerical modeling is related to the infirmity of the LDC prediction. Increasing the accuracy of estimating this parameter leads to increasing the computer modeling. So the major part of studies on the river water quality is related to measurement, calculating and estimation of this parameter (Kashefipour and Falconer, 2002; Deng et al. 2002; Deng et al., 2001). If the Pollution transmission mechanisms in the river with various geometries were specified, the river water quality managing does by more accuracy and his leads to reduce the effects of river pollution on public human's health. Study on the mechanism of Pollutant transmission in the river is a major part of the Knowledge of Environmental Engineering (Riahi- Madvar et al., 2009). When a source of pollution released into the river, Due to molecular motion, turbulence, and non-uniform velocity in cross section of flow, quickly spread to the entire section and covered all the section and moved along the river with the flow (Holzbecher 2012; Chanson 2004). LDC is a function of the hydraulic and geometry characteristics of the river and also its path, so it is very variable and sensitive. Thus, a minimal change in the hydraulic conditions and river geometries, cases the very much fluctuation in its values. Many empirical formulas have been proposed for calculating the LDC. These formulas are usually obtained by classical regression. Some of these formulas are collected Table (1) (Seo and Baek, 2004a; Seo and Cheong, 1998, 2001; Shen et al., 2010; Seo and Baek, 2004b; West and Mangat, 1986; Seo et al., 2009). To calculate the LDC usually a trace is injected in river and along the river some stations should be considered for getting the sample and the tracer concentration in each sample should be measured. To this purpose, the first station should be considered after the completely spreading the tracer in all the flow cross section. The LDC will be calculating by a method such as Dispersion Routing Method (DRM). A brief instruction of DRM will be given in the methodology section. Some researcher to obtain more detail of dispersing process in the longitudinal and over the cross section of river uses a powerful tool such as image processing technique, Acoustic Doppler Current Profiler ADCP and so on(Carr and Rehmann, 2007). These tools helped to the researcher for