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The Soil-Water-Balance (SWB) model has been developed by USGS to allow estimates of potential recharge to be made quickly and easily.

Required Input

Four gridded datasets are required:

  • Hydrologic soil group
  • land use/land cover
  • Available soil-water capacity
  • Surface-water flow direction

In addition to gridded land-surface data the model requires tabular daily climatological data (daily precip (inches), average air temperature [F], max air temp [F], min air temp [F]). Additional data may be required depending on model options:

  1. daily average wind speed (m/s),
  2. daily average relative humidity (%),
  3. daily max relative humidity (%),
  4. daily percentage of possible sunshine (%).

Finally a lookup table must be supplied to assign curve numbers, interception values, rooting depths, and maximum daily recharge values.

Creating an SWB Simulation

To create an SWB simulation, do the following:

  1. Right-click on the "Project Icon.svg Project" item the Project Explorer and select New Simulation | SWB.

A new "Simulation Data" Simulation Data Icon.svg item will appear in the Project Explorer, along with a "SWB Simulations" Simulation Folder Icon.svg item and a new simulation Simulation InactiveIcon.svg item. Right-clicking on the "SWB Simulations" Simulation Folder Icon.svg item also has a New Simulation command that allows adding additional SWB simulations to the project.

Simulation Menu

Right-clicking on the simulation item Simulation InactiveIcon.svg in the Project Explorer will bring up the following menu command:

  • Delete – Removes the simualation item.
  • Duplicate Creates a copy for the simulation, including all parameters set in the model control.
  • Rename – Allows changing the name of the simulation item.
  • Model Control – Opens the Model Control dialog where the model run parameters are set.
  • Model Check – Looks for potential errors in the model setup. Brings up the Model Checker dialog if issues are discovered.
  • Export SWB – Generates files used in the model run.
  • Launch SWB – Starts the SWB model run and opens the Simulation Run Queue dialog.
  • Save, Export, and Launch SWB – Combines several other commands together. First, it saves the project file, then exports files for the model run, and finally launches the SWB model run.
  • Properties – Opens the Properties dialog which displays the simulation properties and allows adding notes.

SWB Output Files

After running the model, SWB will generate several output files.

  • Recharge daily statistics – Contains the minimum, maximum, and mean values for all major components of the water balance for all grid cells in the model on a given day.
  • Recharge daily report – Contains values representing the individual daily values summed over the entire model multiplied by the conversion factor.
  • Recharge annual statistics – Contains mean values representing the annual sum of daily mean values.
  • Log file – Contains a report of the processes performed during the model run.
  • Grid and image files – Based on the selected optional output variables in the model control.

External Links