MODEL NAME AND VERSION: VFSMOD-W Vegetative Filter Strips Design and Modeling System, v2.2.x, May 2003

DESCRIPTION: VFSMOD-W is a complete design-oriented computer modeling system (VFSMOD-W). The  MS-Windows32 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 vegetative filter strip design, uncertainty and sensitivity analyses menu-driven components. 
   VFSMOD, the core of the modeling system, is a computer simulation model created  to study hydrology and sediment transport through vegetative filter strips (VFS).  The model comprises the following: a) a finite element solution is done for the  overland flow equations for the strip; b) infiltration within the strip is  computed using the Green-Ampt method for unsteady rainfall; and c) sediment  deposition and filtration is modeled using an implementation of the Univ. of  Kentucky grass filtration model. This model formulation effectively handles  complex sets of inputs similar to those found in natural events. The  improvements of this combined model over previous models are the inclusion of:  a) state of the art description of flow through the filter; b) changes in flow  derived from sediment deposition; c) physically based time dependent soil water  infiltration; d) handling of complex storm pattern and intensity; and e) varying  surface conditions (slope and vegetation) along the filter. The model is  targeted at studying VFS performance on an event by event basis. VFSMOD, when  combined with the upslope source area input preparation utility (UH), becomes a  powerful and objective VFS design tool. Although the model was originally  developed as research tool, VFSMOD-W can now be used by planners and regulators  to design optimal filter strips for specific scenarios, and to determine  relative effectiveness of existing VFS.
   The design objective implemented in VFSMOD-W is to find optimal constructive  characteristics (length, slope, vegetation) of a VFS to reduce the outflow of  sediment from a given disturbed area (soil, crop, area, management practices,  design storm with desired return period) to  achieve a certain reduction in % sediment (i.e. that for TMDLs). In the  MS-Windows VFSMOD-W modelling system, versions 2.x and up, the design task is  automated. The projects for each combination of design inputs are automatically  created within the program GUI after the user selects a range on the desired  parameters. This new version also automatically produces combined analysis  output tables. Additionally, the program provides two powerful tools. Once the  optimal design parameters are selected an uncertainty analysis can be conducted  using the graphical tools provided. The objective of this analysis is to  identify the level of confidence that the adopted design has against the  uncertainties present when selecting the model inputs. Finally a sensitivity  analysis procedure is included in the GUI to identify the parameters to which  the model is more sensitive for a given scenario, thus allowing the user to  economize effort by focusing on better identifying just the sensitive  parameters.
   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.

DISTRIBUTION: via WWW
USA: http://www3.bae.ncsu.edu/vfsmod

CONTACT INFORMATION: 
R.Munoz-Carpena (carpena@ufl.edu), University of Florida
J. E. Parsons (john_parsons@ncsu.edu), NC State University  

MODEL INPUTS:
- Vegetative Filter Strip length and slope
- Vegetation characteristics including surface
- Vegetation characteristics including surface roughness, average height roughness, average height
- Green-Ampt infiltration parameters for the filter
- Design storm or event hyetograph for the area
- Source (disturbed) upslope area characteristics (dimensions, slope, crop practices and NRCS runoff and erosion parameters)

MODEL OUTPUTS:
- Detailed outputs on transport and deposition of sediment within the filters
- Detailed outputs on runoff depth and velocity within the filters
- Summary outputs showing sediment in and out along with infiltration within the filters (this is used for the design guide)
- Filter effectiveness indicators
- Analysis of sensitivity of selected parameters (if desired)
- Uncertainty analysis of modeling inputs (if desired)
- Design response curves to identify optimal filter dimensions or vegetation cover to achieve user defined runoff/sediment reduction rate (if desired).

RELATED PROJECTS: Hatch USA-CSREES S-1004 Regional Project: "Development and Evaluation of TMDL Planning and Assessment Tools and Processes"

DISCLAIMER: 
VFSmod was originally developed in the Department of Biological and Agricultural Engineering by Dr. Rafael Munoz-Carpena under the direction of Dr. John E. Parsons. The model and associated documentation is supplied as-is with no warranty - explicit or implied. The model is provided to as an educational, research and planning tool. This version is the fourth 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 do ask that you reference our work if you find it helpful in your pursuits.

NEW FEATURES IN RELEASE V2.2.XX
I) New, more intuitive, menu labels and lay-out
II) Expanded and improved sensitivity and uncertainty analyses procedures. Individual filter areas or combines source-filter areas can be now analyzed individually. Multi-dimensional analysis is also available as well as print-out of graphical results. Ranges of user selected parameters are now automatically checked against physically admissible values.
III) VFSMOD and UH have been further refined to improve integration with the GUI environment and graphical inputs.
IV) Improved handling of special cases (small runoff, impermeable surfaces, saturated soils, etc). 

NEW FEATURES IN RELEASE V2.00.XX
I) Model now packed together with MS-Windows GUI for Design and Modeling.
II) The new integrated package now includes design, sensitivity and uncertainty analysis under the program GUI.
III) Enhaced web and PDF documentations, including new a manual Part to discuss the MS-Windows package
IV) Extensive program help built into the MS-Windows (GUI) 

NEW FEATURES IN RELEASE V1.06:
I) Fixed problem when incoming sediment was 100% fine. This was caused by a line out of sequence in sediment filtration subroutine (step3.f). Fixed.
II) changed affiliation of one of the authors. 

NEW FEATURES IN RELEASE V1.05:
I) New way of handling a sediment filled strip (grassed.f) . After this happens (NFUP=1), all the sediment inflow is routed to the outflow end (no deposition) and without stopping the simulation. This way the simulation summary (*.osm) now shows realistic trapping efficiencies and mass balance (outmass.f).
II) Sediment trapping subroutine (step3.f) re-worked to avoid problems with equilibrium slope Se in some cases that led to NaNs.
III) Output format for saturated hydraulic conductivity changed to exponential.

NEW FEATURES IN RELEASE V1.04b:
I) Windows GUI to handle UH and VFSMOD programs now available. Both fortran codes modified to produce outputs suitable for the GUI.

NEW FEATURES IN RELEASE V1.04:
I) Input preparation program, UH
A program for preparing VFSmod inputs is included as integral part of this release. UH uses readily available data to automatically create VFSmod the following input files: a) rainfall hyetograph; b) runoff hydrograph from source area; and c) erosion loss from source area and sediment concentration in runoff. The utility is based on the following methods:
- Generates rainfall hyetographs using SCS method
- Generates runoff hydrographs using SCS curve number method and Unit hydrograph method
- Erosion estimates done using a version of the modified Universal Soil Loss Equation for storm events
- Modifies the Rainfall erosivity factor ± three options
II) Project files added
VFSmod (and UH) now handle project files. This enables the user to use any naming convention and directory structure for inputs and outputs.
III) Improved model outputs
New output files give more details on the simulations and a new output summary file summarizes filter performance (*.osp)
IV) Updated and expanded documentation.
The manual has been revised and now contains numerous new sections on model use, reference tables for inputs to use in the model, and new documentation on the UH utility. An on-line version of the manual can be found on the web site and a PDF version is included in the distribution files.
