How to create river segments with each segment representing 24 hours flow?

[AlexSmajgl]

Hi all
My GIS expert is struggling for weeks to create segments of a large river network, where each segments represents approximately 24 hour flow time. The length of each segment would need to depend on the DEM only as we don't have detailed information on river channel width. Essentially, the greater the elevation difference the longer the resulting segment. My staff tried many things including the river segmentation function but he seems to be doing something wrong as the number of segments is too high AND we get multiple segments running in parallel within the river channel. Can somebody point me at a manual or does somebody have some example code to solve this seemingly simple task?
Cheers, Alex  

[MarkBoucher]

I have no code or book.

You have to have the velocity in the river based on slope. Without a detail hydraulic model, you can only estimate. If you have varied "roughness" (smoother vs rougher), that can influence velocity. You should be able to Google "estimate river velocity" and find something. Length(ft) = Velocity (ft/sec) X Time (sec). If you have a dem you can created a slope raster. Somehow use that to come up with how far the flow would go in 24 hours. You must have a long river.