Flow behaviour in model open-channel bends and implications for lateral migration in rivers

Abstract

An investigation was conducted at he Burnabay mountain Experimental watershed at Simon Fraser University to study flow behavior of single and consecutive model open- chanel bends with curverture ratio combination of 1.0<rc/w<4.7. Detailed measurements of velocity, curent direction and bed topography were colected from more than ten cros sections in each bend. The total bend deflection angles varied betwen 75 and 180 degres. The results of data analysis are presented in isovel paterns, vertical and longitudinal variation of velocity, shear stres and friction coeficients. The transverse secondary flow advection upstream of the bend becomes apreciable at 30 degres and is maximizes at 60 degres. Betwen 80 and 120 degres, the transverse secondary flow decreases to its former magnitude at he straight entrance; shear stres and boundary friction both decrease also. These flow parameters are periodic every 30 to 60 degres of the bend. Hickin’s postulate on the shift of the core of maximum velocity is verifed in single and upstream bends but he downstream bends are influenced by inherited structure which delays the cros over and the location of the fuly developed flow zone. Bends of rc/w>2.7 generate an ascilatory flow stracture with relatively higher amplitudes than tighter bends