FTPro - Rivers and Rainfall

Master TMO

Does anyone know if FTPro takes rainfall into account when it lays out rivers? I've got a couple of large arid deserts in my world, but FTPro is quite happy to lay out a large river network across it. I don't know if it's something I'm doing wrong, or just normal for the software and I'll have to get in and clean them up manually.

Thanks in advance

jslayton

On the Select River Length dialog there is an option labeled "Potential River Flow" that selects between using the rainfall (unchecked) or not (checked) in its computations. The way that FT finds rivers is to compute rainfall at each point on the globe and then to compute the amount of water that's uphill from each point. This result is thresholded by using the value on the River Length slider to get the final river.

Unless the rainfall in an area is zero then FT will be able to find water by going upstream across the terrain. The river model doesn't take evaporation or wind into account and so once water is present in an area it remains there to contribute to the rivers. Yes, it is a flawed model.

Note, however, that there are some good examples of rivers that run through desert including the Nile and Colorado. These rivers begin in wetter uplands and have enough water to make it to the ocean.

Another peculiarity of FT's river model is that it does not allow for endorheic rivers or lakes. The first thing the river flow computation do is to create a temporary surface and fill basins on that surface. If you have a basin then FT will appear to run a river down one side and up the other because FT does the temporary basin fill. This result occurs because the temporary and final surfaces aren't the same.

Master TMO

Thanks for the information. I had had the Potential River Flow box checked, not knowing what it did.

Skaran

Incidently satellite images of the Sahara Desert apparently show river courses through the desert. They just no longer have any water in them! So if you are exporting the rivers to Campaign Cartographer when you are tidying the rivers up you can perhaps change the line styles of these to something else.

JimP

not visual photos, but infrared and radar images show the rivers. There were alligators, etc. living there. Earlier, marsh land type dinos. Couldn't find any photos via google.

Master TMO

I'm trying to mess around with Incise Flow now to create riverbed areas, including in my deserts. Just gotta find the right settings to use.