Experimental investigation of secondary flow strength in the river bends

Understanding of the strong transversal flow due to centrifugal force in meanders leads to detecting the location of maximum erosion in outer bank. By identifying the best sites for constructing the intake structures and proper river training techniques, it is possible to prevent destruction of structures and farmlands which located near the rivers. This article focuses on the experimental study of secondary flow strength, its changes in meanders and models predicting the location of the maximum lateral erosion rate. The experiments are carried out at a sharp bend with the central radius-width ratio of 1.31 on a developed topography and discharges of 63, 89 and 104 liter per second. Investigations indicate a complete correlation between secondary flow and transversal bed slope and also between the reduction of the secondary flow strength and increasing discharge. To make it clear, the ratio of transverse to longitudinal kinetic energy has dropped from 43 percent at discharge rate 63 liter per second to 35 percent at discharge rate 104 liter per second. Also, the place of the intake on sharp bend can be in 1/3 from the entrance of the bend. Moreover, evaluation of phase lag models in the secondary flow showed that they lack the ability to correctly predict the location of maximum erosion. It may be the result of disregard for the sharpness of the bend (the ratio of central radius to canal width) which is highly effective for transversal flow pattern.