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A normalized design procedure to meet sediment TMDL with vegetative filter strips

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 256-261 in Total Maximum Daily Load (TMDL) Environmental Regulations: Proceedings of the March 11-13, 2002 Conference, (Fort Worth, Texas, USA)  701P0102.(doi:10.13031/2013.7566)
Authors:   Rafael Muñoz-Carpena, John E. Parsons
Keywords:   vegetative filter strips, modeling, TMDL, sediment, hydrology design, computer program, water quality

This paper presents a vegetative filter strip (VFS) design procedure to meet sediment TMDL using the graphical modeling system VFSMOD-W. The core program, the vegetative filter strip model VFSMOD, simulates overland flow and sediment dynamics within the VFS based on vegetation, soil type, and topography. The inputs to run the model (rainfall hyetograph, and source areas runoff hydrograph and sediment load) are automatically generated by the system based on a user given design storm (in terms of return period) and application area characteristics (crop system and soil type). These inputs are generated using a combination of the NRCS curve number method, the unit hydrograph, and the modified Universal Soil Loss Equation based on topography, land use and soil type. With this tool, a design example for representative conditions in the Piedmont region of North Carolina is presented (clay and sandy-clay top soils). Simulations were conducted representing a ratio of source area to filter length from 3:1 to 258:1. Rainfall totals for return periods T=1,2,5 and 10 yrs (54-103 mm), were used to generate 6-hour storm hyetographs and runoff hydrographs from source areas with a mean slope of 2%. The optimal filter design can be obtained when setting an objective TMDL (75% sediment reduction) over the programs graphical output. Analysis of VFS performance including graphs showing sediment delivery ratios is presented to demonstrate the utility of this approach.

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