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Title: TRAPPED MULCH INCREASES SEDIMENT REMOVAL BY VEGETATIVE FILTER STRIPS: A FLUME STUDY

Author
item JIN, C. - UNIV. OF MINNESOTA
item Dabney, Seth
item Romkens, Mathias

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2002
Publication Date: 7/1/2002
Citation: JIN, C.X., DABNEY, S.M., ROMKENS, M.J. TRAPPED MULCH INCREASES SEDIMENT REMOVAL BY VEGETATIVE FILTER STRIPS: A FLUME STUDY. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. Vol. 45(4), p. 929-939. 2002.

Interpretive Summary: Vegetative filter strips and crop residue mulches both help to reduce soil erosion on agricultural land. When crop residues become detached and move downslope in runoff, their on-site soil erosion protective effects are lost. However, if these residues become trapped on filter strips, the filter strips' erosion control effectiveness may be increased. Few investigations have been conducted concerning this subject matter. 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 filter strips. The resulting mulch barriers increased flow depth at the upstream edge of the filter and increased filter strip sediment trapping efficiency by 10% to 60%. The trapped mulch barriers created deep slow velocity areas where sediment could settle out of runoff water before reaching the filter strip itself. More than 60% of trapped sediment was deposited in the area upslope of the filter strips, where it could contribute fertility to future crop production. The interactions we observed between crop residue mulches and filter strips suggest that combining residue management (reduced tillage) systems with vegetative buffer strips offer potential synergies for increased conservation effectiveness. These results will benefit farmers and conservation planners who must create erosion and sediment control strategies that maintain the long-term productivity of agricultural lands while improving water quality.

Technical Abstract: Vegetative filter strips and crop residues are effective methods of soil erosion control. 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's erosion control effectiveness may be increased. We investigated the impact of upslope detached surface mulches on the sediment trapping capability of simulated filter strips. 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. Added mulch did not greatly affect the flow depth and velocity inside a filter strip, but 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. More than 60% of sediment deposition took place in the area up-slope of the filter strip. Observed interactions of crop residue mulches and filter strips suggest that combining residue management systems with vegetative buffer strips containing a upslope edge of strong vegetation offer potential synergies for increased conservation effectiveness.