Sediment particle selectivity and its response to overland flow
hydraulics within grass strips
Abstract
Particle selectivity plays an important role in clarifying sediment
transport processes in vegetative filter strips (VFS). 10-m long grass
strips at slopes of 5○ and 15○were
subjected to a series of silt-laden inflows experiments with different
particle sizes to investigate the sediment transport and its response to
overland flow hydraulics. The inflow sediments came from local soil,
river-bed sand, and mixed, with median particle size d50 of 39.9, 207.9,
and 77.4 μm, respectively. Three independent repeated experiments were
carried for each treatment. The results show that when the sediment
trapping lasted for a certain length of time, the re-entrainment of some
small-sized particles was greater than the deposition; that is, negative
deposition occurred, which was not erosion of the original soil.
Negative deposition of particles is mainly determined by the particle
diameter. The coarser the inflow sediment particles and/or the steeper
the slope, the coarser the particles can be negatively deposited.
Deposited sediment causes the VFS bed surface to become smooth and
hydraulic resistance decrease exponentially. Stream power P is more
suitable than shear stress τ of overland flow to be used to
describe the process of sediment particle transport in VFS. The
relationship between P and d50 of outflow sediment is very consistent
with the form of power function with a constant term. These results are
helpful to understand the physical process of sediment transport on
vegetation hillslopes.