Investigation of hydrodynamic characteristics with three types of vegetation accumulation at trash racks

Abstract

The accumulation of aquatic vegetation in open channels, such as leaves, weeds, and large wood, poses a threat to the safety of hydraulic structures and disrupts the normal operation of hydropower stations, resulting in substantial economic losses. Studying the hydraulic characteristics with vegetation accumulation is a prerequisite for solving this engineering challenge. The effects of vegetation accumulation on the hydraulic characteristics with three types of vegetation were investigated using experimental and numerical simulation methods. The results indicate both backwater rise and head loss increase exponentially with blockage ratio. Furthermore, vegetation accumulation results in an uneven vertical distribution of streamwise velocity, leading to the formation of low-velocity regions and backflow vortexes in the upper water layer. For all cases, the bottom gap velocity increases markedly, forming a high-velocity jet region. The maximum jet velocity remains constant in the near wake region and the decay rate in the far wake region is positively correlated with the blockage ratio. Bed shear stresses in the corresponding region are 1–6 times higher than before vegetation accumulation, increasing the potential for riverbed erosion. This study extends the existing knowledge of vegetation accumulation hydrodynamics to provide a basis for the safe operation of hydraulic structures and river management.