Southern Research Station

Title: Modeling sediment trapping in a vegetative filter accounting for converging overland flow

Author: Helmers, M. J.; Eisenhauer, D. E.; Franti, T. G.; Dosskey, M. G.

Date: 2005

Source: American Society of Agricultural Engineers, Vol. 48(2): 541-555

Description: Vegetative filters (VF) are used to remove sediment and other pollutants from overland flow. When modeling the hydrology of VF, it is often assumed that overland flow is planar, but our research indicated that it can be two-dimensional with converging and diverging pathways. Our hypothesis is that flow convergence will negatively influence the sediment trapping capability of VF. The objectives were to develop a two-dimensional modeling approach for estimating sediment trapping in VF and to investigate the impact of converging overland flow on sediment trapping by VF. In this study, the performace of VF that has field-scale flow path lengths with uncontrolled flow direction was quantified using field experiments and hydrologic modeling. Simulations of water flow processes were performed using the physically based distributed model MIKe SHE. A modeling approach that predicts sediment trapping and accounts for converging and diverging flow was developed based on the University of Kentucky sediment filtration model. The results revealed that as flow convergence increases, filter performance decreases, and the impacts are greater at higher flow rates and shorter filter lengths. Convergence that occurs in the contributing field (in-field) upstream of the buffer had a slightly greater impact than convergence that occurred in the filter (in-filter). An area-based convergence ratio was defined that relates the actual flow area in a VF to the theoretical flow area without flow ocnvergence. when the convergence ratio was 0.70, in-filter convergence caused the sediment trapping efficiency to be reduced from 80% for the planar flow condition to 64% for the converging flow condition. When an equivalent convergence occurred in-field, the sediment trapping efficiency was reduced to 57%. Thus, not only is convergence important but the location where convergence occurs can also be important.

Keywords: Flow convergence, grass filters, hydrologic modeling, overland flow, sediment trapping, two-dimensional overland flow, vegetative filters

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Citation

Helmers, M. J.; Eisenhauer, D. E.; Franti, T. G.; Dosskey, M. G.  2005.  Modeling sediment trapping in a vegetative filter accounting for converging overland flow.   American Society of Agricultural Engineers, Vol. 48(2): 541-555