Two separate documents are accessible for VO, a User’s Manual and a Reference Guide. This current document, the User’s Manual, contains information on how to use the program and complete descriptions of all features. This manual does not concern the background theory. The Reference Guide contains all of the hydrologic theory behind the program and gives guidance for users to select or measure object parameters. The history of the development of the model is also addressed for advanced users who need to know “why” and from “where”.