How to get your rivers in the right place

[Redrobes]

In my example there are two exits off of the map where water could reach the sea. I am going to show later that water will chose just one of these. If you put down your rivers so that they followed the blue lines then that would be good. Here is a diagram with the blue lines perpendicular to the contour lines. Our rivers should be on these lines somewhere. What were expecting is that a lake with rivers should form in the thick blue section. If one side of the map had an inflow of water then it would run into the lake and out of the other side. If there was no inflow then the lake would drain to one side only because you can only have one exit. What happens to the river bottom right depends on whats past the bottom right side but we should get something here because all the water within that catchment area has to go somewhere.

[Redrobes]

So providing you come up with something that fits the bill then it would be alright.

I have run a simulation and got it to predict where the rivers would be based on some rainfall. I set it up so that either side of the map was an exit for water. The result is below. The middle part of the map started as a lake and then drained to one side. The middle of the map is an area of confusion so almost anything could have happened and it would have been reasonable.

What was fixed tho is that all the rivers follow the blue lines meaning that they are perpendicular to the contour lines and thus running downhill as fast as it can. Also no rivers crossed the pink lines of the catchment area borders because those lines determine which way water flows. Thats how we can predict where the rivers should be on a map without having to resort to a simulation.

I am attaching a movie in MPG format to show the simulation running. I hope this will show whats going on and why it was fairly easy to predict where the rivers would have been from the height terrain. Though a lake forms in the middle it is unsustainable and one side won out - in this case the right hand side.

[Caenwyr]

So providing you come up with something that fits the bill then it would be alright.

I have run a simulation and got it to predict where the rivers would be based on some rainfall. I set it up so that either side of the map was an exit for water. The result is below. The middle part of the map started as a lake and then drained to one side. The middle of the map is an area of confusion so almost anything could have happened and it would have been reasonable.

What was fixed tho is that all the rivers follow the blue lines meaning that they are perpendicular to the contour lines and thus running downhill as fast as it can. Also no rivers crossed the pink lines of the catchment area borders because those lines determine which way water flows. Thats how we can predict where the rivers should be on a map without having to resort to a simulation.

I am attaching a movie in MPG format to show the simulation running. I hope this will show whats going on and why it was fairly easy to predict where the rivers would have been from the height terrain. Though a lake forms in the middle it is unsustainable and one side won out - in this case the right hand side.

Hi Redrobe! I'm still pretty new on this forum, but I'm working my way through as many topics as possible. I just came to this tutorial and I must say I really like it! As a geographer I can confirm every bit of information you give here. When it comes to the quoted post though, I was wondering if perhaps you could tell me the software you used for this simulation. I would be very interested indeed! Especially since I'm looking for a "natural" way to draw rivers in my map.

Many thanks in advance!

[mssandhu]

Good tut! I do have a question - I have been struggling to work how to get the same look to rivers that you find in any good atlas - they start thin, meander in very 'random' line pattern and join up to get wider until finally ending in a delta or an estuary. When I try, the rivers obviously come out looking overly smooth sided, and they do not start with near invisible thin streams that eventually coalesce to form a river. Any ideas please? (PS I have only just started using GIMP 2.8 - never realised until friends told me that there was anything better than Microsoft Paint!)