Submitted to: International Journal of Sediment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/1999
Publication Date: 3/1/2000
Interpretive Summary: Vegetative filter strips are viewed as an effective erosion-control technique on long slopes, at end-of-field situations, etc. The function of filter strips is to retain suspended sediment in runoff from upland areas. This is being accomplished by decreasing the sediment transport capacity of flow by reducing flow velocities and by serving as a filtration mechanism. While substantial experimental work has been done on sediment trapping by vegetative filter strips, quantitative/mathematical descriptions of this process are notably absent. This paper reports on experimental findings of sediment trapping by simulated vegetative filter strips in controlled laboratory studies that relate trapping or deposition of sediment to a number of factors including the hydraulic flow regime, slope steepness, and filter density. The data obtained for the different vegetative filter conditions were fitted to an exponential decay function in which the constants reflect the experimental conditions. This information will be very helpful in designing filter strip widths and for soil erosion prediction technology of land uses that involve vegetative filter strips.
Technical Abstract: Vegetative filter strips have been widely used for controlling soil erosion from agricultural land, road sides, construct sites, and other disturbed lands. The most important characteristic of a filter strip is the sediment trapping efficiency. Yet, not many studies have been conducted to quantitatively describe the trapping process and trapping efficiency. In this paper, the results of a laboratory study are presented. In the study vegetative filter strips were simulated with polypropylene broom bristles of different densities. Results show that the deposition process in filter strips is described by a time decreasing, three-parameter exponential relationship. The parameters vary with both bristle density and flume slope steepness. Bristle density and flume slope steepness are two important factors in determining the trapping efficiency. As bristle density increased from 2,500 bunches/square meter to 10,000 bunches/square meter, trapping efficiency increased to about 45%. When slope steepness increased from 2% to 4%, trapping efficiency decreased from 50% to 5% for the low bristle density and from 90% to 50% for the high bristle density. Over 80~90% of the sediment deposited upstream from the entrance of the filter strips. Most of the sediment trapped had a particle size greater than 150 micrometers. As the flume slope steepness increased, deposition occurred further down into the filter strips and the sediment passing through the filter strips became larger in size. Flow rate and sediment concentration in the studied ranges (1.45~7.0 liters per second for flow rates and 1.71~7.0 kg/cubic meter for sediment concentrations) hardly impacted the trapping efficiency.