Vegetative Filter Strip Modeling System

VFSMOD-W (http://carpena.ifas.ufl.edu/vfsmod) 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.

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: i) finite element solution for the overland flow equations; ii) Green-Ampt infiltration method for unsteady rainfall; iii) Univ. of Kentucky grass sediment deposition and filtration; and iv) 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 indentify 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 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 (visit http://carpena.ifas.ufl.edu/vfsmod/citings.htm). 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 on-line program help). This version of the model uses inputs that are easily obtainable from tables and other sources contained in the manual.