Trapped mulch increases sediment removal by vegetative filter strips: a flume study

摘要

Vegetative filter strips and crop residues are effective methods of soil erosion control on agricultural land. When crop residues become detached and move downslope in runoff their on-site soil erosion protective effect is largely lost. When a filter strip traps residues, the filter strip '5 erosion control effectiveness may be increased. Few investigations have been conducted concerning this subject. In this study, we investigated the impact of upslope-detached and transported surface mulches on the sediment-trapping capability of simulated filter strips. Results showed that mulches (pine needles) added in random orientation floated parallel to the direction of flow and then turned perpendicular to the flow when they accumulated in front of a filter strip. The width of the resulting mulch barrier depended on the amount and length of the needles supplied to the flow. Shorter needles resulted in denser mulch barriers. A mulch barrier did not greatly affect the flow depth and velocity inside a filter strip, but it retarded the flow and caused a hydraulic jump upstream from the filter strip. Sediment-trapping efficiency was increased by 10% to 60% compared with the same flow slope; and filter strip conditions without mulch. Increases in sediment trapping were most significant in long-duration tests with low-density filter strips or high slope steepness. The backwater formed by a mulch barrier increased the effective length of a filter strip, and more than 60% of sediment deposition took place in the area up-slope of the filter strip. The physical strength of the upslope edge of the filter strip that supported the mulch barrier determined long-duration functionality. Observed interactions of crop residue mulches and filter strips suggest that combining residue management systems with vegetative buffer strips containing an upslope edge of strong vegetation offer potential synergies for increased conservation effectiveness.