Hi all,

I am trying to calculate the topographic wetness index for an area and know the formula, but somehow get an error everytime I try. There are so many different approaches on the internet that I am not sure which to use and why it does not work for my project.

Can anyone tell me exactly how to use my layers with the formula?

Your help is very much appreciated.

I am trying to calculate the topographic wetness index for an area and know the formula, but somehow get an error everytime I try. There are so many different approaches on the internet that I am not sure which to use and why it does not work for my project.

Can anyone tell me exactly how to use my layers with the formula?

Your help is very much appreciated.

Try: Ln((???FLOWACC??? * 900) / Tan(???SLOPE???))

You are missing a few critical steps. I would recommend looking at this thread

http://forums.arcgis.com/threads/32896-from-DEM-to-CTI?highlight=CTI

I also have this model available in our gradient toolbox.

http://evansmurphy.wix.com/evansspatial#!arcgis-gradient-metrics-toolbox/crro