Study of the Effect of Discharge and Bed Roughness on the Maximum Solute Diffusion Length in a Parabolic Channel

Document Type : Research Paper

Authors

1 Ph.D Candidate, Department of Water Engineering, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran

2 Associate Professor, Department of Water Engineering, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran

3 Professor, Agricultural Engineering Research Institute, Karaj, Iran

4 Professor, Department of Water Engineering, Faculty of Agriculture, Isfahan University of Technology, Isfahan, Iran

5 Assistant Professor, Construction and Environmental Engineering Department, University of Napoli Federico II, Napoli, Italy

Abstract

Diffusion processes of contaminants are important processes in channel because of their  effect on environmental pollution and health. In the present research, the effect of different levels of bed roughness coefficient and discharge rate on transverse diffusion coefficient and on the maximum solute diffusion length was studied in a non-rectangle channel. Three levels of bed roughness coefficient of about 0.2, 0.04 and 0.06 along with three levels of discharge of about 5, 10 and 15 L/s were tested: Sodium chloride was used as the soluble tracer. It was injected in to  the water at the upstream cross section. In the water tracer concentration as well as the velocity profile were mined at eight cross sections of 3, 4, 5, 6, 7, 8, 9, 9.5 meter from upstream. The results indicated that the values of the transverse diffusion coefficient varied between 0.23 and 0.56 (cm2/s) and diffusion length values ranged from 108 to 170 (m) for different treatments. As regards constant bed roughness coefficient, increasing the value of discharge can increase diffusion length. Therefore, in constant input flow, roughness coefficient is shown to exert  subtractive effect on diffusion lengths. The shape of channel affects the velocity profile, and this is why nonlinear equation was considered to calculate transverse mixing coefficient at different levels of bed roughness coefficient and discharge. In addition, an equation was also developed to explain the maximum diffusion length in a parabolic channel.

Keywords

References

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Iranian Journal of Soil and Water Research
Volume 46, Issue 3 - Serial Number 3
October 2015
Pages 395-404

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