This GIS menu item is available only when WRDB is being used as a BASINS plugin.
BASINS automatically downloads historic data from a variety of sources (see the BASINS File | Download Met Data and Download Data). These data are stored in a variety of formats that are not amenable to display and analysis. You can import previously downloaded BASINS datasets into the currently active WRDB Project and Working table by selecting the data you want from this form:
Considerable Stations data is usually present in the GIS layer and is used to update/add to the WRDB Project's Stations table.