What is the tool to take a flow length and coverts the longest distance in a polyline path?

Question

I have a flow length raster that shows the range between the lowest flow path and the longest flow path. I need to take the longest flow path and actually draw out the path. What is the best way to do this? I cant use ready use services and not use the advanced license of ArcGIS.

ChrisDonohue__GISP · Answer

If you have access to the Spatial Analyst extension, typically, the next step would be to run a "Flow Accumulation", followed by a "Stream to Feature".  Note that the Flow Accumulation may require a few runs with different settings to come up with a usable output.

Source:  Deriving runoff characteristics—Help | ArcGIS for Desktop

Flow Accumulation—Help | ArcGIS for Desktop

Stream to Feature—Help | ArcGIS for Desktop

The final part, finding the longest flow path from the many lines output in the "Stream to Feature" can be a challenge if you don't want manually go through the output linework and sum lengths.  See the below thread for some ideas on how to automate this.  Note - I have not tried it, but the python script posted by Luke Sturtevant  looks promising.

using the Flow Length tool in Spatial Analyst's Hydrology Toolbox to find the Longest Flow Path

Chris Donohue, GISP