WWHM3 gives the user greater modeling flexibility and options. Version 2 was limited to drainages of less than half a square mile (320 acres) because of the lack of a conveyance feature (natural channel or pipe). This limitation does not apply to WWHM3; with Version 3 the user can model entire watersheds of unlimited size as long as they are contained within a single county or use the time series element to transfer flows from one county to an adjacent county.

Specific changes and additions in Version 3 include:

• Icons are now called elements in the Schematic screen.
• There are separate elements for trapezoidal ponds, irregular ponds, tanks, and vaults.
• Basin land use categories now include land slopes (flat, moderate, and steep).
• Landscape vegetation is now called lawn.
• Runoff credits have been replaced with specific categories to disperse roof runoff to lawn, etc.
• Standard residential has been removed, although the user can still explicitly input the standard residential assumptions.
• Two lateral basins (pervious and impervious) have been added. Flow can go directly from a lateral basin to another basin without a connecting conveyance system.
• A flow splitter now offers greater flexibility in deciding how to separate the flow.
• The open channel conveyance element has been added.
• Gravel trench beds have been added.
• Wetponds have been added. Wetponds can be used to model wetlands and areas influenced by high groundwater.
• There is no longer a Point of Compliance icon (or element). The user can specify a point of compliance at any element by right clicking on that element and selecting “Point of Compliance”. There can be multiple points of compliance. The model keeps track of each one.
• There is no longer an Extender icon (or element). The user now explicitly links one element to another.
• Preferences has been replaced by View, Options.
• View/Export Time Series has been moved into Tools and additional options have been added.
• WWHM3 supports up to 500 elements (if you need more let us know).

There are three GIS Import-related files:

1. Import File (csv): basin land use data
2. RCHRES Import File (csv): open channel data and connections
3. Configuration File (csf): column connections file created in WWHM3 that can be later read by WWHM3 to assist in the input of basin and open channel data.