EXPERIMENTAL STUDIES OF FACTORS IN DETERMINING SEDIMENT TRAPPING IN VEGETATIVE FILTER STRIPS

Abstract

Sediment trapping in vegetative filter strips (VFS) was studied in a laboratory flume with simulated vegetative filter strips (VFS) of different densities, flume slopes, flow rates, sediment materials, and concentrations. Results showed that VFS density, flume slope, and sediment particle size are the major factors in determining sediment deposition. Flow rate had a minor effect, and sediment concentration hardly affected sediment deposition. The trapping process varies with time accord-ing to a three–parameter exponential relationship with the parameters related to the bristle densities and flume slope. Trap-ping efficiency increases with vegetation density and decreases with slope. When the VFS density increased from 2,500 to 10,000 bunches/m 2 , the trapping efficiency increased by about 45%. As slope increased to 4% or 6%, the VFS with densities of 2,500 and 10,000 bunches/m 2 failed to trap sediment. Over 80% of the sediment trapped by the VFS deposited in the approach channel to the VFS and in the upper half of the VFS. Most of the deposited sediment particles were larger than 150 µm in diameter. As the slope increased, deposition moved downstream and deposited sediment became larger.