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Old 12-13-2020, 02:47 PM   #1
Michael Thayne
 
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Default Can the hydrology of this world be made to work?

I'm working on a bronze-age fantasy setting based largely on ancient Egypt with a dash of Mesopotamia thrown in. I decided I didn't want the world to be too exact an analog for Earth, so I flipped a coin to determine the hemisphere (result: southern hemisphere) and rolled dice to determine the direction of the river flow (result: west to east). But otherwise, I've been using Egypt as my main inspiration for things like the physical environment and supportable population density, with a region resembling the Levant to the south, and some wooded mountains inspired by the https://en.wikipedia.org/wiki/Zagros_Mountains added at a point roughly equivalent to the Nile's first cataract.

I'm concerned that this may not work hydrologically, though. If there's nothing but open ocean to the East, the climate should be more like the Yangtze river valley than the Nile river valley. I think I can solve that by having my setting's Big River empty into a relatively narrow sea with another large land mass not too far to the east, so I can justify the east coast desert. But I think I still might have a problem with the Big River's basin not getting enough rainfall to produce the Nile-like floods necessary to support the population density. I'm thinking of maybe flipping east and west across the entire settingóor is there a way I can avoid that? The idea of making the setting's physical environment subtly weird in ways that make perfect logical sense once you have all the information is something that appeals to me, assuming I can make it work.
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Old 12-13-2020, 04:56 PM   #2
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Default Re: Can the hydrology of this world be made to work?

Have you checked the peruvian Caral civilization? They were presumably contemporary with the Egyptian Pyramids, and were seated around 3 rivers. It might help you with your setting.
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Old 12-13-2020, 07:02 PM   #3
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Default Re: Can the hydrology of this world be made to work?

Iím not very knowledgeable about hydrology, but I can think of two ways to get reliable annual flooding and two ways to get a desert for your river to flow through.

The flooding can depend either on snowmelt or on seasonal rains. The desert can be produced either by the high pressure belt in the horse latitudes or by a rain shadow. Mostly thatís easier with the river running between two latitudinal bands of climate (i.e. north or south), but you might like to look into the way that a seasonal analogue of the katabatic effect results in the Tibetan plateau producing the monsoons of South Asia.
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Old 12-14-2020, 03:00 AM   #4
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Default Re: Can the hydrology of this world be made to work?

Wot Agemegos said. The early civilisations along the Indus come to mind.
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Old 12-14-2020, 09:47 AM   #5
Michael Thayne
 
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Default Re: Can the hydrology of this world be made to work?

Quote:
Originally Posted by Agemegos View Post
Iím not very knowledgeable about hydrology, but I can think of two ways to get reliable annual flooding and two ways to get a desert for your river to flow through.

The flooding can depend either on snowmelt or on seasonal rains. The desert can be produced either by the high pressure belt in the horse latitudes
This was my initial thinking. But if you look at the prevailing winds around the latitudes most of the world's deserts are, they tend to run from east to west. This is why southern China is so much wetter than the Sahara, in spite of being at roughly the same latitude.

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or by a rain shadow.
This is sort-of what I'm thinking by having my not-Nile drain into a relatively narrow sea with significant land masses to the east of the sea. But it leaves the question of what generates the rain that feeds the not-Nile.

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Mostly thatís easier with the river running between two latitudinal bands of climate (i.e. north or south), but you might like to look into the way that a seasonal analogue of the katabatic effect results in the Tibetan plateau producing the monsoons of South Asia.
From what I understand though, monsoons mainly hit the east coast of Asia, due to the way the Coriolis effect causes winds blowing towards the equator to deflect to the west. This is why I say it might work better if I flipped west and east for the whole setting design.
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Old 12-14-2020, 10:52 AM   #6
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Default Re: Can the hydrology of this world be made to work?

You could also shift the river north or south, to change its position relative to this planet's analog of Hadley cells. Or if you really want to make it not an analog of Earth, spin the planet the other way around.
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Old 12-14-2020, 11:10 AM   #7
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Default Re: Can the hydrology of this world be made to work?

Wouldn't it be easier to have the wind be the breath of the river god - one breath in and one breath out per year?
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Old 12-14-2020, 12:04 PM   #8
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Default Re: Can the hydrology of this world be made to work?

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You could also shift the river north or south, to change its position relative to this planet's analog of Hadley cells.
Hmmm. So maybe something like the Patagonian desert, or Gobi desert? Though I think those are both noticeably colder than Egypt/Mesopotamia, where I'm drawing all my cultural inspiration from, and I'm not sure either ever hosted a river civilization. Plus, for reasons I'm somewhat unclear on, the Gobi doesn't extend all the way to the eastern coast of Asia. Maybe if that region were flatter the Gobi would extend further east?

On the whole, maybe I could get on board with this idea if I had a better sense of all the implications for the setting, but I'm not sure what those implications are.

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Or if you really want to make it not an analog of Earth, spin the planet the other way around.
This crossed my mind but I'm not sure it's coherent. What do "east" and "west" even mean independent of the planet's spin?

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Wouldn't it be easier to have the wind be the breath of the river god - one breath in and one breath out per year?
That's not quite the flavor I want. That sort of thing implies "mythology all the way down", whereas I want a world that has a purely natural layer underneath all the supernatural stuff. Though could maybe see myself invoking a portal to the elemental plane of water, or a permanent weather control effect, somewhere in the highlands of the not-Nile's basin.

An option that hasn't been discussed is to have the not-Nile deflect either significantly north or significantly south once it's gotten ~100 miles beyond the "first cataract" / "Zagros mountains" region. But I'm concerned the results would be very unnatural looking on a bird's eye view of the map.
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Old 12-16-2020, 02:45 PM   #9
Michael Thayne
 
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Default Re: Can the hydrology of this world be made to work?

Looking more at it, Bangladesh's summer monsoons do seem to blow from the southwest. Translating to the southern hemisphere, maybe having a monsoon from the northwest feeding my river basin would work?
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Old 12-16-2020, 03:53 PM   #10
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Default Re: Can the hydrology of this world be made to work?

You could use a double set of rain shadows: the winds blow in from the east, hit the first and lower set of mountains, then pass over a dry region before hitting a second set of higher mountains and getting completely wrung out.

As for turning the river north or south, could you tilt the river instead, giving it a slight incline into wetter latitudes?

You know, looking at a map... are the Tigris and Euphrates too crooked for you (if you mirrored them over the equator?)
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