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I like this thread. Understanding physical geography is essential to creating a map of realistic, earth-like landforms and waterforms.
Rivers
These are good rules for a strong foundation. Here are some other things that I've noted at the risk of re-stating something in the foregoing thread. Rivers do drain into the sea, but sometimes that sea is an inland sea, or an endorheic basin. I live in an endorheic basin. I like to think in terms of 'watersheds,' although it's usually easiest just to look where the river is going. A watershed is a family of streams and rivers that eventually all join into the same river that drains into the ocean or an inland sea. Any river in the real world that flows into the Great Lakes of North America, the Great Salt Lake, the Dead Sea, the Aral Sea, the Caspian Sea, or the Baikal, is by definition part of an endorheic basin. There are many more.
In physical geography, not only the landform determines the path of the water channel, but also the amount of water. For example, a river discharging a lot of water passing over nearly flat land will meander in a different proportion to a small river passing over a nearly flat surface. The truth is that the rivers in my world are probably all violating the actual 'wave' that they should form since I have neither the ability nor the inclination to calculate this. However, the general principal is that the more water that is discharging through the channel, the bigger the meanders are. Geology has a whole sub-discipline for shapes of rivers called river morphology or fluvial geomorphology and it is generally way more than I want to know, but it is nice to be aware of.
On my Asdar world map, mountains are denoted by simple lines since the scale is large (1 inch represents 80 miles). For this reason, I can get away with the shape of my rivers. When I make a regional map and define the contours of the landforms, the rivers must observe these landforms as they flow ever downwards. I must also take into consideration the climate and the amount of rainfall.
It is possible for a river to drain a great body of water into the sea. The St. Lawrence River drains from Lake Ontario into the Gulf of St. Lawrence (North Atlantic Ocean).
The Thames River (346 km) is pretty short compared to the Nile, the Amazon, or the Mississippi. However, due to Britain's notorious rainfall, it is a very broad, navigable river and its average discharge is about 66 cubic meters per second. The Ishim River (2,450 km) in Kazakhstan, is about seven times as long. Its average discharge is about 56 cubic meters per second. The size of the watershed and the climate are the basis for how much water a river must discharge by the time it reaches the ocean or the inland sea into which it disembogues. Seasonal rainfall can also change the behavior of a river as residents around the Mississippi well know. Arroyos or Wadis in Arizona and Arabia that are dry or mere trickles most of the year can become raging rivers during sudden thunderstorms that cause 'flash floods.' I indicate Wadis on my Asdar map with a dotted line.
The Shadew River (pronounced SHAY-juh) on Asdar is inspired by the Brahmaputra-Ganges River in the real world. Rain and glacial meltwater feed into this river for probably over 3,000 km. It passes over the division of tectonic plates, cuts a nice canyon, has some glorious waterfalls, and then finally passes through a great delta into the Pallathantic Sea. The delta area is probably too large with regard to the river's length. I justify this by saying that the tectonic rising of the subcontinent of Pytharnia has forced the great discharge of the Shadew River to make new channels over many tens of thousands of years, so the river cuts down as the earth rises up. The Shadmouth, or mouth where the Shadew River enters the delta is easily over two kilometers wide. The nation of Bangladesh is striped with the braids of the Ganges River, however, it is relatively flat.
Inland bodies of water
I take the other extreme and tend to have lots of lakes, perhaps too many, in the world of Asdar. I am careful to place them in climates where there is sufficient rainfall. However, the 'Sea of a Thousand Curses' is quite large and rests in a desert region. Its saltiness is somewhere between the ocean and the 'Dead Sea' of earth. It has been shrinking since the Ice Ages, but is still quite vast for an inland sea. I justify this by saying that it has survived from before the end of the Ice Ages.
Originally Posted by Redrobes
