MWSWAT 2009 is a plugin for MapWindow, an Open Source GIS system available from http://www.mapwindow.org which runs under the Windows operating system. The MWSWAT 2009 plugin, which is also open source, is downloaded as a Windows installer.
Install MapWindow first, then run the MWSWAT 2009 installer. MWSWAT 2009 will appear in the Plug-ins menu the next time you start MapWindow.
You will also need to download and install the SWAT 2009 Editor, also available from the SWAT web site. With the current version 2.2 of MWSWAT 2009 you need version 2009.93.7a or later of the SWAT 2009 Editor. Install it by unzipping and running Setup. Use the default installation folder so that MWSWAT 2009 can find it.
You can install MWSWAT 2009 as well as MWSWAT, and make them both available as MapWindow plugins at the same time. If you run MWSWAT 2009 on an existing MWSWAT project it will, after warning you and giving you the opportunity to cancel, convert the Default scenario to SWAT 2009. You can also run MWSWAT on an MWSWAT 2009 project and again, after a warning, it will convert the Default scenario to a SWAT 2005 project. To do these conversions you must be sure to write all files during step 3 "SWAT Setup and Run".
Two example watersheds have been created, San Juan in Mexico and Linthipe in Malawi. Initial geo-processing for these watersheds is described in the geo-processing document, and the use of MWSWAT to set up and run SWAT on them is described in the MWSWAT tutorial document, both on the documents page. MWSWAT 2009 is almost identical in operation to MWSWAT. The other resources, maps and weather generator files, that you need for them are in two zip archives:
The source code is available from the MapWindow subversion repository at http://svn.mapwindow.org/svnroot/MapWindow4Plugins/MWSWAT. This is best accessed by a tool like Tortoise.