How to get your rivers in the right place

[Neorael]

I wanted to thank you all. Every part of this topic has something to contribute in the learning of how the hydric sistem operates

[Midgardsormr]

The alluvial plain near a lowland river tends to be very fertile because the soil around it is regularly exchanged. While the "Fertile Crescent" eventually wore out and suffered from desertification due to overfarming, the Nile's flood plain, particularly the delta area, remained fruitful through thousands of years of continuous farming. The primary difference was that the Nile floods regularly, which refreshes the nutrients in the soil. The Tigris and Euphrates flood plains have remained fertile, but not to the same extent because their flooding is less reliable. The rest of the land in that area was merely irrigated from the rivers and did not receive the benefit of the floods. As a result, the nutrients were depleted, salt levels rose, and the desert claimed what was once very good farmland.

More obviously, of course, vegetation tends to be thicker around rivers because that's where the water is! In the American Great Plains (where I grew up), the tall grasses will grow everywhere, but you only naturally find trees near the rivers because the rest of the land just doesn't have enough moisture to support them. Trees planted far from the rivers tend to be rather sickly, and they often fall down during windstorms. Typically on someone's car.

[Elothan]

I have collected a bit of the information in this thread and some more in a pdf. I made it for my own use, but if anybody wants it to read off line I`d be happy to share it
It is mostly just copy paste from the forums (with credits and links to the contributors, so nothing really fancy.
But if it is ok, just ask and i will put it up

[Gidde]

Go ahead and post it up, pdf collations are always welcome.

[Elothan]

Go ahead and post it up, pdf collations are always welcome.

Rivers and Lakes

I will probably expand on this document with what I learn along the way in relation to mapping

[necrominog]

Was just directed to this thread. Very informative. Thanks!

Now to correct the error of my ways...

-nog

[Niedfaru]

Fantastic thread. Collates a lot of information that will be very useful to a lot of people. One thing I need to ask is: what happens in wetland areas. What causes the high amount of groundwater in these areas and how does this impact on river flow and lake formation in them? Considering there are some very large wetlands in the world, and in a pre-industrial world such and the ones most people here seem to map, I'd think they'd be a major feature on the land around.

[jbgibson]

Think of the 'shape' of the top of a world's groundwater as being an alternate surface of the planet. Everywhere it's above 'ground level' there's water - river, lake, ocean. Everywhere it's below the dirt/rock surface, it's an underwater reservoir or flow. The two surfaces are related - if the dirtlevel dips, the water that's 'exposed' is fluid instead of contained between rock particles, and it puddles. That modifies the shape of surrounding groundwater to match at the new shoreline.

The wetlands you mention are just where the two surfaces almost match. Yup, one would assume in the days before people succeeded in draining or filling in wetlands to make use of the land, there would've been more. Wetlands can be source of streamflow, or destination, or a intermediate pause. Figure they constitute lakes that are almost filled in (which is sometimes how they form) or flattish land that has acquired an overabundance of water (can you say "flood"? I thought so :-) ).

Too bad marshes are so tricky to depict!

[Niedfaru]

So a wetland isn't so much a feature that can easily be mapped, but more a collection of small lakes with extremely wet ground between them? I'm assuming on a modern topographical map, wetlands would only be visible as a large oddly shaped collections of lakes and streams? I mean I tried looking at maps of the Everglades, and of the local marshes around me here in Southern England (although most of ours are man-made, or at least drained, quarried and then reflooded at fraction of their original size), and it's pretty hard to even make out where they are. It's just really, really green with a lot river and lakes in it. The Qurna Marshes in Iraq don't even show rivers very clear, and only a small patch of water. Considering the Mesopotamian Marshes were once over 7000 square miles, it seems important to figure this stuff out, especially as this map seems to show Iraq breaking almost every river police rule in this thread.

[macziggy]

I would just like to add another exception to the rules here... It may have already been mentioned so forgive me if it has, I haven't had the time to read the entire thread... The Casiqure (probably spelt wrong) Waterway in Brasil and Venezuela is a unique and natural feature that links two completely separate large rivers in the Amazon jungle, both rivers also continue their own paths towards the sea and are both very large and long bodies of water... The Amazon and Orinoco rivers. It is an important highway for the local indigenous people and as far as I know one of the only, if not the only example of this happening on the planet.

Also the Mesopotamian marshes that have been mentioned in Iraq are called the Shatt Al Arab and it is the meeting point of the river Tigris, Euphraties and a third large river running from Iran, whose name a ashamed to have forgotten and cannot be bothered to look up right now. All three rivers meet a few miles before they meet the sea and the area is extraordinarily beautiful and thought to be the inspiration behind the biblical and Islamic stories of the Garden of Eden. luckily for me I am fortunate enough to have seen it in person - Not so lucky considering the circumstances at the time