University of FloridaDepartment of Agricultural & Biological Engineering


VFSMOD-W: Vegetative Filter Strip Modeling System



In memory of John E. Parsons (1952-2005) - our mentor and friend.


Vegetative Filter Strip Modeling System (VFSMOD-W) is a design-oriented vegetative filter strip modeling system. The MS-Windows graphical user interface (GUI) integrates the numerical model VFSMOD, a utility to generate source (upslope disturbed area) inputs for the model based on readily available NRCS site characteristics (UH), and advanced uncertainty and sensitivity analysis, inverse calibration and design menu-driven components.

Vegetative Filter Strip Modeling System (VFSMOD-W)

VFSMOD, the core of the modeling system, is a computer simulation model created to study hydrology, sediment and pollutant transport through vegetative filter strips (VFS). The model comprises the following modules:

  • Finite element solution for the overland flow equations.
  • Green-Ampt infiltration method for unsteady rainfall.
  • University of Kentucky grass sediment deposition and filtration.
  • A new contaminant transport component (first implemented for pesticide reduction of Sabbagh et al., 2009).

The advantage of VFSMOD-W over other models used to simulate VFS pollution removal is the inclusion state of the art description filter hydrology including changes in flow derived from sediment deposition, physically based time dependent soil water infiltration, handling of complex storm pattern and intensity and varying surface conditions (slope and vegetation) along the filter. This model formulation effectively handles complex sets of inputs similar to those found in natural events. The model is targeted at studying VFS performance on an event-by-event basis and when combined with the upslope source area input preparation utility (UH or others like PRZM), becomes a powerful and objective VFS design tool. The design paradigm implemented in VFSMOD-W seeks to identify optimal filter constructive characteristics (length, slope, vegetation) to reduce (to a prescribed reduction target like a TMDL) the outflow of pollutants from a given disturbed area (soil, crop, area, management practices, design storm return period). Additionally, the program provides three powerful tools. The sensitivity analysis allows the user to identify important parameters for a given model application and simplify model calibration. An automated inverse calibration algorithm serves to identify effective model parameters when measured field data is available. Finally, after the filter design exercise, uncertainty analysis can be conducted to identify the level of confidence that the adopted design has based on propagating the input uncertainties onto the model outputs.

VFSMOD-W has been tested in a variety of settings (agroforestry, mining and roads) with good model predictions against measured values of infiltration, outflow, and vegetation trapping efficiency for sediments, phosphorus (particulate and dissolved), and pesticides. Although the model was originally developed as research tool, is now widely used by consultants, planners and regulators to design optimal filter strips for specific scenarios or to assess effectiveness of existing VFS.

Documentation for the model is available in several forms (web, printable PDF and online program help). This version of the model uses inputs that are easily obtainable from tables and other sources contained in the manual.


Vegetative Filter Strip Modeling System (VFSMOD) was developed in the Department of Biological and Agricultural Engineering, North Carolina State University USA, by Dr. Rafael Muñoz-Carpena under the direction of Dr. John E. Parsons. The model is now maintained by Dr. Muñoz-Carpena at the Agricultural and Biological Engineering of the University of Florida (USA).

The model and associated documentation is supplied as-is with no warranty - explicit or implied. The model is provided to you as an educational and research tool under the terms of the Open Source Initiative, Educational Community License, Version 2.0

This version is the fifth moving the model from a research tool to one available for general users. As with any model, the results are totally dependent on the user's ability to wisely select input parameters that represent the "field" and to interpret the results. We will make every effort to provide assistance and encouragement as our other commitments allow.

We will make every effort to provide assistance and encouragement as our other commitments allow. We do ask that you reference our work if you find it helpful in your pursuits.

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This page was last updated on October 07, 2012.