Mountain River Three Gorges Reservoir acoustic Doppler velocimeter aquatic plant biomechanics aquatic plants backwater effect bed shear stress bed-load transport bedload check dam drag-reducing flows environmental variables experiments flood flow resistance flow type flow velocity measurements fluvial hydraulics friction factor granular beds gravel-bed stream groyne field groyne type heavy metals hysteresis in-stream structures local bed shear stress logarithmic law of the wall morphology mountain stream