Flow pattern study in Beshar River and its two straight and meander reaches using CCHE2D model

Abstract

In this study, flow pattern in Beshar River as a main branch of Karoon River has been analyzed using CCHE2D. For this purpose, a 12-km reach upstream of Shahmokhtar hydrometric station near Yasuj city was considered. The CCHE2D model was calibrated using different Manning’s roughness coefficients and different turbulent models; for this purpose, numerical results were compared with observation data for three different discharges. The results showed that for the medium and high discharges, less Manning’s roughness coefficients (0.015 ≥ n ≥ 0.025) and for low discharge, higher Manning’s roughness coefficients (0.035 ≤ n ≤ 0.050) are more suitable. Also, k–ε turbulent model is more effective in this study. Besides, variations of hydraulic parameters like water depth, velocity, shear stress and Froude number are calculated and discussed. The analysis of the flow and velocity pattern in the straight and meander reaches of the river shows that the changes trend of the water surface gradient and velocity in the cross sections of this two reaches are different. Due to effect of secondary currents, latitude gradient of the water surface and depth average velocities increase to the outer bank of the bend. But in the straight reach, latitude gradient of the water surface is almost zero and the maximum velocities are in the center-line of flow. The R-squared (RSQ) and linear correlation coefficient (r) factors between velocity and shear stress show that there is linear and direct relationship between these two hydraulic parameters in the entire study reach.