Dear List(s) BASIC Original Question: Is there a free watershed modeling extension for ArcGIS Spatial Analyst? Answer: No. Tim Loesch did mention that ESRI is developing a data model for watersheds - this may be where the student's idea came from. A few suggested I ask 3x developers if they have plans to upgrade their extensions to 8.1 platform, good idea but out of my scope right now. I appreciate all of the feedback given regarding the existing extensions for 3.x. When you load SA for 3x you do get the hydro.avx, and hydrov11.avx extensions and you can also get the WshdDel.avx extension from the ESRI ArcScripts page. I am grateful for all of your responses. Below are a list of web sites containing downloads and other information regarding watershed modeling and ArcView GIS (all 3x none for 8.1)~ by no means is this a complete list . .. just a summary. EPA's BASIN http://www.epa.gov/OST/BASINS BASIN1 extension from Dr. Ivan Petras http://gis.esri.com/arcscripts/details.cfm?CFGRIDKEY=1435867339. Recommended to read his article on using DEMs in watershed modeling prior to using the extension. Contact: Petras Ivan Keith Casperson referenced a few extensions I have not checked out yet from spatial-online. http://www.spatial-online.com/ARCFLOW.htm http://www.spatial-online.com/ARCFLOWBasin.htm Thanks Greg Slutz for this helpful link too~ http://www.crwr.utexas.edu/gis/gishyd98/watchar/watchar.htm ************************************************************************** Catherine L. Hansen Training Coordinator chansen@rowekamp.com Rowekamp Associates, Inc. 1601 E. Highway 13, Suite 201 Burnsville, MN 55337 Phone: (952) 882-4776 Fax: (952) 882-4779 www.rowekamp.com Toll Free: 888-356-4315