Through the use of user-defined variables, users can create their own models within WEAP.  Collections of user-defined variables can be packaged into "Plugins" so that they can be added to an existing WEAP area all at once.  

A plugin contains a set of user-defined variables, built-in variables for which you have changed the default expression, user-defined units used by those variables, event scripts, other files, a short description (up to 1000 characters) and complete documentation (in rich text format).  

Each WEAP area can have one or more plugins loaded.  Use the Plugins screen (below) to manage the plugins for the current area, and to create new plugins to use in your other WEAP areas or to share with others.  

The following shows an example of a simple plugin named "Reservoir Evaporation (Hargreaves)" that is loaded into Weaping River Basin:

Highlight a plugin from the list on the left to see its details on the right.  In the example above, the Summary tab shows the plugin's name (in bold), short description, list of the built-in and user-defined variables (both data and result), and a version history.  The Variables tab gives the full details on all included variables; the Events tab lists any included event scripts (e.g., Before Calculation, After Scenario Calculation); the Files tab lists any included files; the Notes tab shows the full documentation.  

The toolbar at the top gives access to a variety of options for managing plugins:

Menu option: Advanced, Plugins