Data Requirements

The following is an overview of data requirements for using Vflo™. See the links provided for detailed formatting and loading instructions.

Digital Elevation Model (DEM)

A DEM covering the area of interest is the source of flow direction and slope values for the Vflo™ model. The DEM is also used to locate channel cells. Having a high-resolution DEM is important for calculating a representative drainage network, locating channel cells appropriately, and obtaining reliable hydrograph results.

There are two options for loading a DEM in Vflo™:

• Use AutoBOP to automatically process DEM data, delivering a hydrographic model for any location.
• Use GIS to manually develop an ASCII flow direction and slope map from the DEM.

Shapefiles

While shapefiles are not required for building a Vflo™ model, loading shapefiles that define key locations, such as channels and basin boundaries, can be useful for model development. Shapefiles may be loaded at any time, see Shapefiles for instructions. Shapefiles used in Vflo™ may include:

• Channels: a polyline shapefile is useful for display and may be used in AutoBOP for two purposes:
  • To assist in identifying the area to be modeled (Vflo™ domain)
  • To enforce channels, augmenting appropriate identification of channel cells
• Basin boundaries: a polygon shapefile identifying the boundaries of the Vflo™ domain is useful for display and may be used in AutoBOP for two purposes:
  • To assist in identifying the area to be modeled (Vflo™ domain)
  • To enforce basin boundaries, important for calculating conservation of volume and obtaining representative hydrographs
• Roads: a polyline shapefile identifying roads may be useful for display.
• Stream gauges: a point shapefile identifying stream gauge locations can be used to identify gauge locations in the Vflo™ model grid. Often, cells with stream gauges are identified as watch points to facilitate calibration.
• Other key points of interest

Landuse/landcover data and Manning's roughness reclassification lookup tables

To develop roughness maps for Vflo™, Manning's roughness lookup tables are used to translate landuse and/or landcover data into roughness values. For a full description and step-by-step instructions, see Formatting parameter maps in GIS: Roughness.

Soil texture data and Green and Ampt reclassification lookup tables

To develop maps for Green and Ampt infiltration parameters (Hydraulic conductivity, Effective porosity, and Wetting front suction), Green and Ampt lookup tables are used to reclassify soil texture classifications as Green and Ampt values. For a full description and step-by-step instructions, see Formatting parameter maps in GIS: Infiltration.

Channel cross sections and hydraulic information

Channel hydraulics may be defined by either:

• Trapezoidal cross sections (Channel cells)
  • Channel width and channel side slope values can be determined by deriving a geomorphic relationship between drainage area and channel bottom width, from as-built plans or surveys, or by other means. Develop ASCII maps using the channel width map and channel side slope map tutorial instructions.
• Rating curves (Rated channel cells)
  • Area-stage and stage-discharge data are required for rated channel cells. See Preparing rating curve and cross section files for formatting instructions.
• Cross sections (Cross section cells)
  • Distance-elevation data pairs are required for cross section cells. See Preparing rating curves and cross section files for formatting instructions. A base elevation value is needed if flow is assumed to begin at some stage above the lowest elevation value of the cross section.

Reservoir data

Storage-stage and stage-discharge curves are required to define reservoir cells. See Preparing rating curves and cross section files for formatting instructions. In addition, an initial storage value representing the storage volume available before discharge occurs may be input for reservoirs.

Additional parameter maps

Not all available parameters must be defined to develop and solve a Vflo™ model. However, developing ASCII parameter maps for the following properties may assist in crafting a representative model. For general instructions on formatting ASCII parameter maps, see Parameter map formatting requirements.

• Baseflow: see Formatting parameter maps in GIS: Baseflow for step-by-step tutorial instructions.
• Soil depth
• Initial saturation
• Abstraction
• Impervious percentage: see Formatting parameter maps in GIS: Impervious for step-by-step tutorial instructions.

Watch point locations

In Vflo™, cells of special monitoring interest are established as watch points. All watch points may be solved simultaneously using the Analyze Basin command. Watch points may be stream gauges, reservoir inflow and outflow locations, control structures, overflow and diversion sites, and other critical locations. To establish these points as watch points, their location within the Vflo™ domain must be known.