Performance Testing of Vegetative Filter Strips

Field experiments on vegetative filter strips (VFS) showed average sediment-removal efficiency varied from 50 to 98% as flowpath length (i.e. width of the VFS) increased from 2.44 to 19.52 m. Almost all of the easily removable aggregates (i.e. aggregates larger that 40 μm in diameter) can be captured within the first five meters of the filter strip. However, the remaining small-size aggregates are very difficult to remove by filtering flow through grass media, as even relatively low levels of turbulent energy in the water is sufficient to keep the finer sediments in suspension. The only effective mechanism for removal of small-size sediments is infiltration. Experiments with low to moderate flow rates on the longer plot lengths showed removal efficiencies of 90% or higher. The sediment removal efficiency of the filter strip does not increase much by increasing the width of the filter strip beyond ten meters. Improved efficiency of VFS can be achieved through the installation of a drainage system (e.g. a French drain) to increase infiltration and by stem-reinforcement of vegetation with various geosynthetic products to reduce channelization of flow and short-circuiting.