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"Non-Carving" Rivers

Started by Eusebio Ptolomeu, December 14, 2024, 03:09:40 PM

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Eusebio Ptolomeu

Apparently, when the map generator is about to place a river in a tile, it lowers this tile's original height. Is it possible to avoid this lowering effect? To make the generator place the river in the tile and that's that?
I can see the reasoning behind it, but when it's time to place a river in the lowest dry-land level, this system lowers the tile so that it becomes underwater, and we end up with looks like a gulf more than a river, in my opinion.

prissi

Which is exactly the intended behaviour as rivers enter the sea form estuaries which even ocean-going vessels can navigate.

Eusebio Ptolomeu

#2
Quote from: prissi on December 14, 2024, 03:18:35 PMWhich is exactly the intended behaviour as rivers enter the sea form estuaries which even ocean-going vessels can navigate.
I see the reasoning. Part of the problem is that I like to import heightmaps instead of using the Simutrans generator, and my heightmaps often have expansive stretches of just-above-water plains, which exarcebates this effect. Is this lowering behaviour something that can be accessed only trough the code, or is it exposed and easily changed somewhere else? Maybe somewhere in the simuconf file?

prissi

Heightmaps can only have water at sea level. When the climate code was introduced, the need for cliffs towards any body of water was gone. However, getting this to heightmaps is non-trivial. Thus, unitl this day, the sea has a cliff while lakes can have flat shores.

Octavius

Interestingly, my experience is that rivers run on ridges, not in valleys. I suppose my experience is a side-effect of growing up in a delta. Yes, it's unstable, that's why deltas change all the time.

I think building a simutrans map of my country based on a heightmap will have to wait: half the country is below sea level. I wasn't planning on doing that anyway.

prissi

Also in the nederlands, before human arrived and civilisation started, rivers were at the lowest point in depressions. But then, then was not much land to start with ...

Octavius

Any low areas quickly filled up with peat or, if a river was flowing through, sand. No real depressions were left, so the rivers avoided the glacial moraines from the ice age, but otherwise had no real preference for any place. The lower parts of the country mostly consisted of peat bogs. I understand it if you don't want to call those land.

Low-land rivers deposit sand in their riverbed, slowly raising their bed. When they flood, they deposit sand on their banks, building them up and slowly rising above the surrounding plain. When people moved in, they tended to live on the riverbanks, because that's where the floodrisk was the lowest. In the bogs, small streams spring.

Eventually, the outside slope of the banks/levees gets so high that during flooding erosion takes over from sedimentation and the river can cut a way through its banks. A completely new river forms and the old river fills up with peat. It's entirely natural and causes natural levees about 1–2 metres above the plains. Without climbing above the plains, rivers wouldn't radically change course. For Simutrans purposes, a single-height slope is, for land traffic, about 4 metres.

In the modern day, humans have changed the process, increasing relief and dropping the plains up to 8 metres below the rivers. Peat extraction lowered the plains, creating lakes; draining of the lakes dried the remaining peat, causing oxidation and sinking. Dykes prevent flooding and deposition of sediments further from the rivers, but between the dykes sand is still deposited. Rivers were made deeper for shipping, but that also made them faster, reducing sedimentation. And above all, humans closed old rivers and made new ones for shipping and flood prevention.

These chaotic changes happen in the Netherlands on a timescale of 500 years or so.