Rivers and reservoirs with rich vegetation resources may suffer from the natural accumulations of vegetative floating matter (VFM) at trash racks. The relationship between hydraulic parameters and physical characteristics of natural VFM accumulations needs to be developed. This research experimentally simulated the natural VFM (leaf-type, fascicled-type, and mixed-type) accumulation at trash racks, varied by flow rate, VFM quantity, and release position. The blockage of cross-section, increase in local head loss, and changes in flow distribution with a natural VFM accumulation were quantified. The results indicate that the hydraulic parameters and physical characteristics of natural VFM accumulations are closely related to the structure of VFM. The head loss and the percentage of gap flow due to the accumulations of leaf type-VFM are numerically lager than that of fascicled-type VFM. Furthermore, the head loss …