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Redrobes
01-01-2009, 08:50 PM
We have had so much talk on this subject and so many maps fail this point that there is a River Police badge now for officers of the CGuild to catch miscreants in the process of making a map with duff rivers.

We have stated many times that water flows down hill and others, especially Waldronate, have given a list of points that must be true for water in a non magical and natural terrain and yet we still have those maps coming in.

So this tut is not so much about what we should be doing with our rivers but exactly how to marry the real world with the pen in your hand.

So first lets state a few really basic known properties about water in a non magical terrain.

1. Water flows downhill and it does so in the direction of steepest decent.
2. Rivers originally start with water which has fallen from rain.
3. Rivers ultimately end in the sea or in rare cases may evaporate into nothing.

We will add more shortly but lets dwell on these for a second.

Point 1: Rivers flow downhill.

If you don't know what is high ground and low ground about your terrain then you cant get your rivers traveling in the right direction. Trying to make terrain heights based on already specified river patterns is hard work. So determine your terrain height FIRST.

The statement also implies that two separate bits of water will always follow the same path. This is generally true. So when two rivers meet they BOTH then travel in the SAME direction. I.e. rivers do not spontaneously fork or split into two and go different ways around an obstacle. Only in a situation where one path cannot take the combined flow from the source does the water then split into different routes. So rivers always join up and do not split up.

Since rivers travel in the direction of greatest decent you cannot have rivers on the top of a hill or along any ridge. In fact when a rain drop falls it goes into exactly one 'Catchment Area' and these areas are usually separated by hills and ridges. A drop of rain just one side of a ridge falls into one catchment area and another just the other side of the ridge perhaps a few feet away go into a different catchment area. Those catchment areas collect the water into streams and rivers and form a 'Drainage basin' and each basin will eventually have exactly one river to the sea. So find the high points in your terrain and divide up your terrain into catchment areas based on them.

If your river enters a zone that in all directions means that it now has to go uphill then you are in a basin. Only in a basin will a lake possibly form. Lakes are a much scarcer geographical item than most fantasy maps have them. When we have a lake it can do one or more of the following :-

1. Fill up until it overflows out with another river.
2. Seep into the ground (i.e. overflow into the ground)
3. Completely evaporates. This is also very rare indeed.

If the lake overflows to another river then it is true that it flows out with exactly one river. It does not fork rivers out from a lake unless there is a temporary swell in rainfall, causing flooding. This is true because if there were two exits from a lake then the level would fall until there were just the lower one to exit the water. If you had two exits the same height then one would erode and the other would silt up. Which one is down to the chaoctic nature of the universe but in geological terms it would happen very quickly.

So you can have multiple rivers entering a lake but only one exit river. In effect a lake is a bit like a very fat bit of river.


A bit more complexity.
================

Rain or a river can hit an area of rock that has big cracks in it or is very permeable. In either case the water can go underground. From here it can gush out of another big crack or cave mouth. The cave mouth can be above or below the level of the surface of a lake. This is a spring.

When rain permeates through pourus ground then it will hit a water table. This is a layer of saturated ground and the water which makes it up travels towards a spring very slowly. The 'surface' of the water table might be horizontal underground or it might vary in height undulating. Where the surface ground terrain height drops away to a level below that of the water table thats where springs will occur and water will drain from the water table feeding the spring. Spring water which has permeated for a very long time in the water table is the stuff thats very pure and often safe to drink. So springs occur part way up a hill side and they are always at a very similar level - i.e. they follow the contour of the terrain. You have to dig a well to a depth to reach past the water table before the well fills with water.

So a bit of terrain comprising of a hill with a cliff on one side cant have wells on the hill. The rain falling on the hill goes into the ground or runs away. That going into the ground will fall out of a cave somewhere on, or at the bottom of the cliff.


Exceptions.
=========

Not many. The main one is that rivers erode terrain and pick up sediment. It can drop this sediment which then prevents the water from flowing in that direction so it much change. Thats called meandering. When the river has passed over a rapids in comparatively soft terrain it will be loaded with sediment. When it then flattens out and slows down it will dump off much of that sediment causing lots of meandering. In those situations the river can 'braid'. It splits and forks into many small rivers all flowing in approximately the same direction. In all but the most rare cases will that river rejoin and come back into one channel again tho.

joćo paulo has pointed out that the largest island where a river has forked around it is a mere 20 square kilometers.
http://www.cartographersguild.com/showpost.php?p=36528&postcount=3
This river is going through its very temporary meanderings to find one course through this region. One day soon one side will dry up. In any case 20 square km is very small.

When a river carries a lot of sediment it can dump it off right next to the sea. For the same reasons the river will braid but instead of rejoining, it hits the sea first. In this case it can form a delta where it spreads out into the sea. These deltas are usually small in comparison to the length of the river. The Nile delta is about 100 miles north-south but then the Nile is 4000 miles long. At the very least a river should have to pick up enough sediment so that its well loaded by the time the delta STARTS.

Redrobes
01-01-2009, 08:52 PM
Ok so far this has been said before so I will show an example of what this means and hope that the example will help people get their rivers is better shape.

I want to make a terrain. To start with we need the terrain height so I will draw on some colored bands to show where the high areas will be.

Redrobes
01-01-2009, 08:54 PM
If I mark on this map where the catchment areas will be and the direction of water within them then you will see that it will flow towards the middle where there will be some uncertainty about what it would do next.

Redrobes
01-01-2009, 09:00 PM
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
01-01-2009, 09:08 PM
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.

EDG
01-01-2009, 10:42 PM
Very interesting stuff - I had no idea about most of this, but it all follows and makes sense when one thinks about it.

I have a couple of questions:

- It looks to me as if the lake would drain to the right in your example anyway, because it looks like the terrain rises up to the yellows/oranges just off the the left of the map. So the fact that it does do that makes sense to me. I'm not sure what the river in the bottom-left quadrant is doing though, it seems to fill into the lake and then the lake retreats from it into the top half of your map and then drains to the right? So where is the river water going from the bottom left while it's doing that, is it just seeping into the ground? (also, what software are you using to do the simulation?)

- One thing I've found curious in the real world is northern canada - if you go look at it on google maps ( http://maps.google.com/ ) you'll see there that a huge swathe of the country around Hudson Bay, is covered with small lakes (you can see this in the map mode really clearly). Where do all those come from? It looks to me like the water table is above the land surface here, is that right? Or is something else going on? (e.g. permafrost in the ground is having an effect?). Actually looking at it, northern Ontario nearest Hudson Bay is actually lacking these small lakes (there are several rivers going to HB instead), and the same goes for southwest of HB, but to the east and west and northwest of HB we're back to lots of lakes. I suspect the geology has an effect here (is the precambrian shield that makes up a lot of canada impermeable, maybe?). That may be one thing to explain here too - the effect of permeable vs impermeable rock that the water is going over.

Thanks for doing this anyway, really interesting stuff!

Nomadic
01-02-2009, 12:34 AM
2. Rivers originally start with water which has fallen from rain.


A river can also be the result of melt water from mountain snowpacks. In fact that is where most of the water comes from where I live (central oregon). When you have a river like this you get high and low points. The highest points usually come during spring and early summer when the snowpack starts melting. Late summer and into fall it tapers off, getting to its lowest in the winter. Winter replenishes the snowpack and the cycle starts over again.

Good look at how rivers form though, very helpful (have some rep).

Talroth
01-02-2009, 01:38 AM
Being Canadian I have to question your view on lakes being more rare than they are usually presented in Fantasy. Honestly most maps I've seen tend to lack lakes in a number I would expect when placed in a northern region that would be subjected to glacier action.

Asharad
01-02-2009, 01:52 AM
Being Canadian I have to question your view on lakes being more rare than they are usually presented in Fantasy. Honestly most maps I've seen tend to lack lakes in a number I would expect when placed in a northern region that would be subjected to glacier action.

Yep, some areas are covered in lakes. If you've flown over southern Louisiana and SE Texas, you know what I mean. Here's an example from google maps.

Redrobes
01-02-2009, 12:34 PM
EDG:
The terrain might raise up to the left but there was a single flat base level which went across the middle of the map to either side. It could have gone either way. It would have been reasonable to have a river going east to west or west to east.

During the sim if the water height is not very much then it does not show so if the water spreads out then it can vanish from the view. I set it not to permeate or evaporate and its running on my GeoTerSys app. There is in fact rain and water all over the map just not very much of it. The app is not ideal either. Its not without problems and differences with the real world. It is objective however, so it can come up with an answer which lacks my bias.

Talroth, Asharad:
Perhaps there are more lakes than I thought. It was a personal observation not really steeped in fact. Our world has some crazy places on it which defies all sensible mapping. Heres a good one...

http://maps.google.co.uk/maps?hl=en&ie=UTF8&ll=21.133824,54.181137&spn=0.589862,0.837708&t=h&z=11

It seems that there is a band across the world from Canada, Norway, Finland, and right across Russia in a small set of latitudes which do have a tremendous amount of lakes. Below that line they get a lot less numerous. But best ignore that statement - some places do have a lot of lakes. I dont know why this is or whether it has anything to do with water tables. I would doubt it. I wonder because of the latitudes that it might be because for some part of the year lots of water is locked up as snow and ice and then later it all thaws into lakes and then refreezes again. Maybe that climate precludes long rivers because theres no continuous steady water flow.

Nomadic:
Sure, should have said rain and snow. It was basically that water has to gain the energy to rise up in height before losing it all as it falls back to the sea.

I am not much of a geographer but have been wrestling with some of these things trying to model them in water flow to try and get the results looking natural. We could do with more expertise with geographers and geologists on this site.

Midgardsormr
01-02-2009, 02:57 PM
For convenience's sake, here's a cross-link to another thread on this topic, wherein some information about deltas and coastal formation was discussed.

http://www.cartographersguild.com/showthread.php?t=2927

I'll also link that thread to this one.

Hoel
01-02-2009, 07:04 PM
We have lakes, lots and lots of lakes of all different sizes. The reason (at leas according to what they told me in school) is the ice age.
The ice ran through the mountains of the nothern hemisphere and gouged out valleys and hollows, You can see them everywhere here, and left huge freshwater seas and lakes. These lakes drained at the end of the ice age but left millions of of smaller lakes scattered about. Since there is a lot of water coming in through rain and snow and less draining due to the shape of the ice age terrain and the colder climate, they're still around.
I grew up on a the bottom of a lake. A 5000 year old lake perhaps, but you can still take a shovel out into the area and find the old sediment layers and see where the shoreline were, it's alot dryer and less fertile soil. The big lake left a string of dozens of smaller lakes, from Hornborgarsjön to Lången.

A side note about the lake, a local amateur archeologist and historian called McKeys wrote a book where he fits the Beowulf saga in around this lake. if you belive his research (it's a bit sketchy but may be plausible) it would have taken place right in my back yard, he even points out a possible burial mound where he could have been buried.
Beowulf would have been called Björn thou, Beowulf=Bee Wolf (Biulv)=Bear=Björn
Now i'm rambling again.

There are lakes, lots of them everywhere. I think we underestimate how many bodies of water there is actually. If you have a nice depression with a trickle of water coming in, there will be a lake, or a pond, or a pool, or a swamp or a puddle.

Nomadic
01-02-2009, 07:09 PM
I wonder if you got the idea for lake amounts by looking at state/country lake maps. For example, a lake map of oregon will show many rivers and only a few lakes. The issue with that is that there are many more lakes then there appear to be (they are all just so small that they don't show up on a state map).

NeonKnight
01-02-2009, 07:18 PM
Some good Info there Red Robes, but just thought I would point out a few 'exceptions' because as we know, ALL rules are all about exceptions ;)

Endorheic lakes (http://en.wikipedia.org/wiki/Endorheic_lake) are lakes that do not drain away to the sea, and as a result any and all rivers/streams etc that empty into one of these lakes never go to sea. The water in these basins leave only by evaporation or seepage into the underlying bed of the basin. Often these lakes are seen on the interior of old Volcano collapsed domes and such, but the DEAD SEA in Israel is perhaps the most famous of these types of lakes, with the Caspian Sea being another famous one.

loongtim
01-02-2009, 09:57 PM
First of all, thanks Redrobes for a great tutorial. I found it very informative.

As far as frequency of lakes go, I live in Windermere ("among the lakes") Florida - can't go 1 mile without running into a large body of water (which, btw, is inevitably infested with alligators). Limestone makes for a very permeable foundation with lots of underground waterways and springs bubbling up everywhere. No mountainous glacial melt for us though.

Gandwarf
01-02-2009, 10:10 PM
The Netherlands has lots of lakes as well, especially in the north. We do not have as many lakes as the Swedes however :)

Redrobes
01-03-2009, 10:34 AM
Thanks Neon, I didn't know the word for that. I think Waldronate mentioned it a long time ago too. I did say that there was three things that can occur for a lake and that was number 3. You can get it with a river too just running into nothing across savannas when the rainy season comes and goes. In either case these are rare tho.

When lakes evaporate only then all the impurities in the water concentrate so the dead sea is salty. That's also occurring in many places in the world where they irrigate crops since all the water is taken up by plants and evaporated leaving progressively salty and infertile soil. Theres some beatiful round shapes in the desert like this which is circular irrigation zones.

http://maps.google.co.uk/maps?hl=en&ie=UTF8&ll=29.966237,38.39859&spn=0.547858,0.837708&t=h&z=11

Oh and I think I had just better say that lakes are in fact extremely numerous and all over the place contrary to what I said before. Perhaps I just live in a land that does not have all that many... :oops:

Ascension
01-03-2009, 02:43 PM
I think the problems with lakes is that people sometimes think of ponds as lakes and then what is the scale of the map. On continental style maps, most lakes would not be seen at that scale. On a regional scale, then, lots of lakes would be seen. On a city scale you could put in as many ponds as you like. Now this is all for a certain amount of realism. If some lake or pond happens to be quite important and you want to put it in, then you're getting into the representational realm and away from the realism. It's the balance that's hard and sometimes we have to compromise one way or the other for the sake of the story.

My 2 bits

NeonKnight
01-03-2009, 03:04 PM
Found this at wikipedia:


Meaning and usage of "lake"

There is considerable uncertainty about defining the difference between lakes and ponds. For example, limnologists have defined lakes as waterbodies which are simply a larger version of a pond, or which have wave action on the shoreline, or where wind induced turbulence plays a major role in mixing the water column. None of these definitions completely excludes ponds and all are difficult to measure. For this reason there has been increasing use made of simple size-based definitions to separate ponds and lakes. In the United Kingdom, for example, the charity Pond Conservation - which works to protect all types of freshwater ecosystem - has defined lakes as waterbodies of 2 hectares (5 acres) or more in area.[3] Elsewhere, other workers have treated lakes as waterbodies of 5 hectares (12 acres) and above, or 8 hectares (20 acres) and above (see definitions of pond). Charles Elton, one of the founders of ecology, regarded lakes as waterbodies of 40 hectares (99 acres) or more, a value somewhat larger than modern studies would suggest appropriate.[4] The term "lake" is also used to describe a feature such as Lake Eyre, which is a dry basin most of the time but may become filled under seasonal conditions of heavy rainfall.

Further, in common usage, many lakes bear names ending with the word "pond", and a lesser number of names ending with "lake" are in quasi-technical fact, ponds. In short, there is no current internationally accepted definition of either term across scientific disciplines or political boundaries. Within disciplines, authors are careful to define environmental geographic circumstances, and obviates the need for artificially imposed definitions when most of the worlds' people speak different languages.

joćo paulo
01-03-2009, 03:18 PM
Scientists say that large rivers flow beneath the Antarctic

source (http://www.apolo11.com/biociencias.php)

:compass:British scientists discovered that rivers, size of major European rivers are at a depth of hundreds of feet beneath the Antarctic ice.

The discovery puts in check the theory that the lakes subglaciais developed over millions of years with autonomy, and that theoretically could harbor primitive forms of life, that would have evolved independently. According to some researchers suggest, if there are microbes in glacial lakes, could also exist in jupiteriana moon Europa or in underground lakes of Mars.

Another consequence of the discovery drill is to review in the deserts of Antarctic ice, with the intention of studying the lakes under the polar cap, where it is believed that there is life.

Previously it was thought water moves under the ice through slow infiltration. But the new findings show that cyclically the lakes beneath the ice cap "overflow", causing massive floods that travel hundreds of miles.

According Duncan Wingham, scientist in charge of the team of researchers responsible for the discovery, "the biggest concern is that delaying the drilling of the lakes is the fear that the equipment may include some microbes from the surface there. The models indicate that any contamination will not be restricted to one lake. "

Using the satellite ERS-2, the European Space Agency, ESA, the scientists measured with great precision the oldest layers of ice and the thick Antarctic continent and found changes in synchronized altitude areas, separated by up to 290 km. According to scientists, the only possible explanation for this change would be the existence of large flows of running water under the ice, and that transfer water from a lake to another.

The discovery of rivers subglaciais creates new speculation that the Lake Vostok, approximately 5,400 cubic km of water - enough to supply Sao Paulo(10 million people) by at least 5 thousand years - may have, historically, produced flooding large enough able to reach the mainland coast.

http://www.apolo11.com/imagens/etc/lago_vostok_2.jpg

NeonKnight
01-03-2009, 04:12 PM
I think your translation may be a little off there joćo paulo.

I think it may be hundreds of feet, not hundreds of miles.

From the following website:

http://www.livescience.com/technology/050407_earth_drill.html


The Earth's radius is about 4,000 miles (6,400 kilometers). The main layers of its interior are in descending order: crust, mantle and core.

The crust thickness averages about 18 miles (30 kilometers) under the continents, but is only about 3 miles (5 kilometers) under the oceans. It is light and brittle and can break. In fact it's fractured into more than a dozen major plates and several minor ones. It is where most earthquakes originate.

But still, cool information know.

Volsung
01-03-2009, 08:13 PM
joćo paulo has pointed out that the largest island where a river has forked around it is a mere 20 square kilometers.
http://www.cartographersguild.com/showpost.php?p=36528&postcount=3
This river is going through its very temporary meanderings to find one course through this region. One day soon one side will dry up. In any case 20 square km is very small.


The link that JP gives in his post actually says the island is 19,000 square kilometers (~12,000 square miles).


The Bananal Island covers an area of 19,162.25 km², twice the size of Lebanon or Jamaica. It is the largest fluvial island in the world being 350 km long and 55 km wide.
From http://en.wikipedia.org/wiki/Bananal_Island

That seems pretty large to me, but, granted, that is a rarity. The largest one I know of is about a square mile and most are a few feet.

joćo paulo
01-03-2009, 09:43 PM
I am embarrassed...

I apologize to everyone.

In this map of the state of Tocantins you can see the size of the absurd that did.
The island in question is in the lower left corner.

TaylorS
03-19-2009, 01:36 AM
Very interesting thread! Given that I'm Minnesotan I well acquainted with lakes, we have thousands of them gouged out by ice sheets during the last ice age. An observation I've made is that besides lots of lakes the glaciers left the local-scale drainage patterns a bit messed up and erratic in places with stream-water going short distances zig-zagging from lake to lake until a substantial river with a flood-plain is reached.

Redrobes
03-19-2009, 07:01 PM
I guess the more modern the geology the more weird its going to look. Even with extremely recent geology the water should still adhere to these general principles because water moves so fast in comparison to changes in rock. Your area showing the zigzags of streams all finding a new and comparatively fresh path to the sea should convince us all that it has to be this way.

TaylorS
03-19-2009, 10:41 PM
I guess the more modern the geology the more weird its going to look. Even with extremely recent geology the water should still adhere to these general principles because water moves so fast in comparison to changes in rock. Your area showing the zigzags of streams all finding a new and comparatively fresh path to the sea should convince us all that it has to be this way.

That is very true. The reason for the messed up drainage patterns is that the ice sheets left a lot of debris, resulting in lots of hills and ridges, and dug out big holes that became lakes. It's actually quite a beautiful landscape

Korba
03-31-2009, 08:41 AM
Geomorphology – i.e. the geographical processes that affect the landscape are of particular interest to me. I have just found this post and would like to add a few points that hopefully those looking for more information will find useful / informative.

Springs


1. Water flows downhill and it does so in the direction of steepest decent.
2. Rivers originally start with water which has fallen from rain.

For this statement to be true you really need to divide water into two categories:

Ground Water
Surface water

For surface water like streams and rivers both of these statements are obviously true.

For ground water the situation is more complicated and your discussion on springs (I feel) needs a little clarification.

There is the type of spring as you rightly say is the source where an underground river or groundwater emerges under the effect of gravity.

In Southern England the usual meaning of spring is where ground water emerges for the first time at the surface and isn’t reliant on gravity.

This effect is reliant on bands of permeable and impermeable rocks or clay. Rain falling on the permeable rock seeps in as you have said until it reaches the impermeable layer. Here the weight of the rock above forces the water upwards to where the two different layers meet at the surface. This is where springs form. If this happens to be at the top of a hill ponds can form in any small hollow. If it happens on the side of a hill a stream forms and begins to fall down the slope.

The Weald of Kent ( http://en.wikipedia.org/wiki/Weald) is a good example of small ponds on hill tops and spring lines on ridges.

Rivers

River outflows:

2. Seep into the ground (i.e. overflow into the ground)

I disagree with this statement, lakes by definition cannot form on a permeable surface. Where a river meets a permeable rock a sink hole will usually form. Where it meets a softer rock a waterfall is likely.

Lakes


Only in a basin will a lake possibly form

It seems a very obvious point, so obvious its rarely thought about but what has caused the placement of a lake. A hole in the ground is too simple because the only type of lake a river on its own produces is an Ox-bow lake that form through meanders and are limited in size and depth to the river that formed them.

So we need other mechanisms to form lakes, or more accurately form the hollows in the ground AND this is the crutch point some way of damming the hole so the water can’t escape.

The large lakes for example those in the African rift valley are formed by plate tectonics. This cause the “natural depression” mentioned earlier that can fill with water. Other examples of a rift valley lake is Lake Baikal ( http://en.wikipedia.org/wiki/Lake_Baikal) which contains 20% of the worlds fresh water.

The Scottish lochs in the Great Glen have been caused by glacial erosion (see more below) along an old transform fault.

Glaciation is a whole different kettle of ball games and opens up a huge range of lake types. Glaciers are capable of gouging massive scars in the landscape but again it requires some fairly specific stages for a lake to form. From the top of my head glaciation forms four types of lakes

Corries / Cirques ( http://en.wikipedia.org/wiki/Cirque)
These form in mountain regions normally on a north facing slope and mark the point a glacier once started, the glacier grinds a basin with a lip at the front which now retains the water.
Usually small in size but VERY numerous in most mountain regions.

Ribbon lakes ( http://en.wikipedia.org/wiki/Ribbon_lake)
A glacier traveling through the base of a valley will erode uniformly, something tat will not form a lake. However an area of softer rock will leave a hole which can then be dammed by end moraine (lots of rock left when the glacier retreats.
Fairly common in upland regions and range from a modest size

Fjords ( http://en.wikipedia.org/wiki/Fjord)
Fjords are in very simple terms a ribbon lake that has been flooded by rising sea levels. Can be very numerous at the right latitude but obviously are by definition on the coast.

Knock and Lochan ( http://www.answers.com/topic/knock-and-lochan-topography)
A unique glacial landscape and one that forms areas with huge numbers of small lakes. I will let you read about it yourself but again glacial scouring leaves small hills (knocks) and small lakes (lochens). The drainage in such areas can be very complicated so feel free to have crazy rivers and lots of boggy ground.

One final type is so rare and unstable but deserves a mention for accuracy are the lakes that form when a glacier cuts across a river valley. Meltwater trapped behind the ice builds up and has in the past formed massive lakes. The effect when the dam burst so to speak is also quite spectacular. Read more about it here - http://www.glaciallakemissoula.org/ but for any GM looking for a 2000ft wall of ice or the geographer looking for how something like the Columbia River Gorge here is a possible explanation.

Volcanoes

Crater lakes are worth remembering and can be quite spectacular. In real life and also on a map.

Gorges

Getting tired now like I’m sure you are reading all this but the important thing if you want a gorge is that unless sea levels change rivers can’t cut through terrain on the lower reaches of the river, it will just go around. Gorges, rills and valleys are possible at the upper reaches of the river near the source due to the river cutting into the terrain but not at the lower reaches unless…

What is more common in forming gorges is that the land is uplifted in some way and the river continues its path and as the land pushes up it appears to cut through the land.

I’m sure I have forgotten something but this is the kind of detail that interests me. Any mistakes feel free to point out.

loogie
05-17-2009, 08:12 AM
yeah, canada has a crapload of lakes, mostly in the norther regions.

These lakes (in the band you mention above) are generally caused by glacial advance and retreat... the glaciers essentially scrape off the land as they advance, and as they retreat, they dump everything they scraped up and move backwards... this creates large holes where the softer rocks wear away faster... but also the deposits the glacier makes can create lakes as well. heres an example of what we mean by a lot of lakes, this is near winnipeg, but areas all along canada have similar lakes.

Ascension
05-17-2009, 08:29 AM
That looks like a lot of fun, fishing, kayaking, etc.

Talroth
05-17-2009, 05:57 PM
That looks like a lot of fun, fishing, kayaking, etc.

Yeah, the only problem is that there is more wildlife to worry about than just the fish,... Namely the number of bugs that are produced in those conditions. You know you're camping trip is going to go poorly when the family dog gets carried off by the black flies.

loogie
05-17-2009, 06:14 PM
yeah at times you can actually hear the buzzing outside.

pickaboo
05-27-2009, 07:58 AM
I'd like to make notice of the fact that the lakes from the ice age glacier retreat can be temporary if shallow enough. Here in Finland I have seen a few examples of shallow lakes that slowly die because they turn to swamps.

HandsomeRob
05-27-2009, 10:26 AM
http://en.wikipedia.org/wiki/Stream_capture
Stream Capture (also known as Stream Piracy) is pretty sweet.

-Rob

pickaboo
05-27-2009, 04:04 PM
http://en.wikipedia.org/wiki/Stream_capture
Stream Capture (also known as Stream Piracy) is pretty sweet.

-Rob

Grazy, and lakes can do that as well.

withlyn
06-26-2009, 06:30 PM
Lakes are common in some areas, generally those with previous glaciation (Canada, Sweden), tectonic rifting (Africa, Baikal) or an extremely high water table (Florida, Louisiana). Mountain lakes are generally some combination of rift lakes and glacial lakes. Volcanic crater lakes are always fun in an adventure, but are relatively rare within any given region. Elsewhere, most lakes and ponds are formed by manmade dams.

Furthermore, all lakes are subject to eventual siltation. Fast-moving water from the incoming rivers and streams is able to suspend a lot of sediment, but when the water slows down in the lake, that sediment gets dropped, gradually filling up the lake. Depending on the size of the pond/lake relative to the size of the basin it drains (and thus its incoming sediment load), this can take anywhere from a few hundred years (Lake Nasser in Egypt, for instance) to millions of years (Lake Baikal, the African rift lakes). To be truly "realistic" then, a fantasy map should have large numbers of lakes only in regions that are swampy, mountainous, or show signs of geologically recent glaciation.

Although the info about lakes not being found on ridge lines and only draining to one river is generally valid, Isa Lake (http://en.wikipedia.org/wiki/Isa_Lake) (actually more of a pond) in Yellowstone National Park is situated on the continental divide at Craig Pass, and actually has two outlets, one which flows to the Pacific Ocean and one which flows to the Atlantic.

Also in Wyoming is Two-Ocean Creek (http://en.wikipedia.org/wiki/North_Two_Ocean_Creek), which splits into two distributaries, one which flows to the Atlantic, and the other to the Pacific.

Just because these things can happen doesn't mean they are normal, or that you would expect them to happen with big lakes or rivers; if you put something like that in a map, make it special!

Feralspirit
06-26-2009, 11:05 PM
Killer post wythlin! I figured there were exceptions to the rules but wasn't quite sure where to look for them. Awesome contribution to this thread. Repp'd!

Welcome to the guild, :).

Ascension
06-26-2009, 11:39 PM
Wonderful. Now everyone will be quoting this whenever we talk about splits :)

waldronate
06-27-2009, 05:57 PM
According to descriptions, Isa Lake only flows in two directions when the water level rises in spring. Two Ocean creek does flow in two directions, but it more seeps out of its meadow on the continental divide than actively splits as we often see in maps here.

Both features are small enough that they wouldn't be visible except on very small local scale maps. The general rules about rivers and lakes aren't affected and budding cartographers should still not be cut any slack for infractions.

Midgardsormr
09-19-2009, 11:50 AM
Crosslink to another post with interesting information: http://www.cartographersguild.com/showthread.php?t=7052&page=3

Juggernaut1981 talks about river behavior, deltas, and Australian sand rivers. Also, Gamerprinter brings up the topic of underground rivers.

Gamerprinter
09-19-2009, 01:00 PM
I learned something on a National Geographic show a few weeks ago that the Great Lakes are rising. At first no one was sure why, and a small science post on Lake Ontario proves the truth of the matter, that the Great Lakes have been rising an inch per year for the last 10,000 years.

Apparently, during the last Ice Age, 4 miles (?) of ice sat above what is now the Great Lakes. The tremendous weight of this ice actually pushed the crust downward hundreds of feet lower than lands south of the Great Lakes. Now that the ice is gone, the crust is still gradually "healing" itself and rising to eventually attain the proper elevation. Thus the Great Lakes are rising. Actually some of the Lakes are getting deeper, while the majority of them are getting shallower.

There's evidence of submerged forestland in about 40 feet of water beneath Lake Huron. This is where its getting deeper. There's a tilting effect caused by the crust rising to the north of it.

I hadn't previously heard of this phenomenon. I found it extremely fascinating and since we seem to be talking River Police (and lakes in the above post) issues lately. I thought I'd add this to the conversation.

GP

Ascension
09-19-2009, 02:00 PM
That is pretty cool. I watched that History Channel show "How the Earth was Made: The Great Lakes" and never knew about the giant salt basin underneath of the lakes and how it is protected by a giant granite dome.

Gidde
09-19-2009, 03:04 PM
Don't feel bad Ascension ... I live here and I didn't know that until I watched the same show.

@GP: Yep, the shallowing of the Great Lakes is really worrisome to a lot of us Michiganders. I didn't know though that it was due to crust rising until I saw your post. Thanks!

Steel General
09-19-2009, 04:23 PM
I wonder if it will have any serious affect on Niagara Falls?

Gamerprinter
09-19-2009, 06:30 PM
I wonder if it will have any serious affect on Niagara Falls?

Actually, Niagra Falls was mentioned in that same show.

Apparently Lake Huron and Lake Erie didn't use to be connected. But with the rising of the Lakes caused the water to be forced over the land between the two lakes, which formed the rivers that joined the lakes. The connection between the two occurred 1800 years ago.

Water from the upper lakes flowing into Lake Erie then Lake Ontario caused the water to flow which eventually formed Niagra Falls. So apparently Niagra Falls is relatively "recent" (in geologic time). The show suggested that eventually the water volume flowing over Niagra Falls will increase, though it may be several thousand years before there's any real kind of disasterous change, due to that.

GP

Gidde
09-19-2009, 07:19 PM
Especially since they're actively slowing the Falls' march. Without intervention, the falls would be gone relatively soon, geologically speaking ... but they've pretty much halted the erosion to keep them in the same place. Add in the effect of the hydro dams, and more water flow shouldn't affect the falls much if at all.

Jeff_Wilson63
09-19-2009, 08:30 PM
The statement also implies that two separate bits of water will always follow the same path. This is generally true. So when two rivers meet they BOTH then travel in the SAME direction. I.e. rivers do not spontaneously fork or split into two and go different ways around an obstacle. Only in a situation where one path cannot take the combined flow from the source does the water then split into different routes. So rivers always join up and do not split up.
I'm a new member, and I apologize if this subject has been beaten to death. I get frustrated myself with rivers that split for no apparent reason. However, we should keep in mind the example of the lower Ganges ( http://maps.google.co.uk/maps?hl=en&ie=UTF8&t=p&ll=22.940689,90.513611&spn=1.259596,1.299133&z=9 ), and that rivers do split sometimes.

This example is probably more useful for retconning existing maps than creating new ones.

waldronate
09-19-2009, 08:55 PM
In the case of distributaries (the lower Ganges, in this case), the water is still following the path of steepest descent. The main channel starts to fill with silt until it is no longer able to carry the entire flow, which forces a side channel that can carry the rest of the flow. This side channel appears because the amount of water + the reduced channel size makes the total water column height greater than the surrounding landscape. This sort of thing is common in deltas all over the world, but the length of the distributaries is always a tiny fraction of the overall river length.
Many of the river splits we see here at the guild take place far up along the river, which is very unstable, geologically speaking, and will not last any significant length of time.

Aylorian
09-23-2009, 05:46 PM
Uhoh, I had no idea there was so much to rivers. It might only be text/ascii maps (right now) but I believe I have the mother of all river violations spreading from one end to the other of a 3000 room continent.

Now I'm going to have to invent some world story about alternative gravity or something :)

Steel General
09-23-2009, 07:13 PM
Uhoh, I had no idea there was so much to rivers. It might only be text/ascii maps (right now) but I believe I have the mother of all river violations spreading from one end to the other of a 3000 room continent.

Now I'm going to have to invent some world story about alternative gravity or something :)

One word for you... MAGIC

Notsonoble
09-23-2009, 09:13 PM
You know, some of this makes no since when looking at a texas map... our rivers split like crazy...

Redrobes
09-23-2009, 09:28 PM
Been scanning with google and see lots of rivers and tribs but no violations so far. Where you looking ? Can you post a map link ?

There are places in flood plains where it goes all over the place but thats expected in a flood plain only cos its changing so fast. Put some gradient on it and it settles into the standard patterns quickly.

pickaboo
09-24-2009, 02:45 AM
Long time, no post..
I was recently in a conference about heat and mass transfer and this river issue came up. Professor Voller (http://www.ce.umn.edu/~voller/) from University of Minnesota and his group are modeling the generation of river deltas and they've shown that significant delta formation can be observed in scale of decades. They use this information in attempt to protect cities from hurricanes there.
This makes me think that we really should sort of use blur on the deltas instead of high-detailed islets and such.

arxhon
10-13-2009, 08:35 PM
Maybe late to the party on the "lakes districts" of Northern Canada (not just Ontario), but here's some additional information:

The crazy number of lakes stretching across northern Canada down to about the 52nd parallel or so is, in fact, due to glaciation, as alluded to in earlier posts. Long story short, the glaciers gouged up the ground beneath them as they advanced (glaciers flow like water, just very slowly), and then deposited ice behind them as they retreated.

The gouges are where lakes formed. The largest and best known glacial lakes are the Great Lakes, of course. Lakes of similar size are Great Slave Lake, Lake Winnipeg and Great Bear Lake.

Glaciers often left behind what is called "knob and kettle" terrain (c.f. eastern Alberta around Cold Lake) as they melted and retreated, which is extremely hilly with small lakes between and around the hills. Interestingly enough, swampy areas are not infrequent due to very shallow lakes being silted up and slowly overgrown with peat mosses, deciduous trees, shallow water plants, and so on (c.f. Elk Island National Park).

Hopefully this has provided enough information for others to do more specific research on their own or as springboards for mapping ideas.

RobA
10-15-2009, 11:29 PM
More interesting stuff. I came across this image at Wikipedia (image has been released to public domain):

17749

This shows all the continental divides in the world. Of note are the grey areas. These represent endorheic basins that do not drain to the ocean (link (http://en.wikipedia.org/wiki/Endorheic)):


An endorheic basin ... is a closed drainage basin that retains water and allows no outflow to other bodies of water such as rivers or oceans. [I]n an endorheic basin, rain (or other precipitation) that falls within it does not flow out but may only leave the drainage system by evaporation and seepage...

Endorheic regions ... are closed hydrologic systems. Their surface waters drain to inland terminal locations where the water evaporates or seeps into the ground, having no access to discharge into the sea... Endorheic water bodies include some of the largest lakes in the world, such as the Aral Sea and the Caspian Sea...[3]

I was stunned at the area these comprise! The river police might need to go back to school ;)

-Rob A>

Ascension
10-15-2009, 11:32 PM
Interesting. I'd like to see rivers superimposed on top to see how that comes out.

rdanhenry
10-16-2009, 03:20 AM
Most endorheic regions are arid; you can see that at a glance.

Most of the lakes in them are quite far inland. Even those that aren't have notable mountains between them and the sea. Most maps with inland lakes don't provide those qualities.

Redrobes
10-16-2009, 08:24 PM
Yes, nice image thx for posting and I agree with subsequent comments. It looks like they have put a grey region as a line between all the basins but I was under the impression that water at the ridge between two basins would fall to one or other sea. I think seeing the rivers on top of those maps would indeed fill in the extra info were looking for. Certainly a river flowing into a desert will dry up, that happens a lot on savanna plains. It evaporates before it reaches the sea. If the climate were more stable and less seasonal then it would probably cut a channel and make a river but it does not get a chance.

jbgibson
12-17-2009, 08:29 PM
Another unusual situation you could use for a really special place is a bidirectional river. The one I can think of, the Tonle Sap (http://en.wikipedia.org/wiki/Tonl%C3%A9_Sap) in Cambodia, doesn't look like a violation of the River Laws on a map. Bidirectional: crazy? No - the "water flows downhill" condition is met differently at different times of year. In its highest flow during monsoon, the Mekong's surface is enough higher than the rest of the year, that the nominal level of the Tonle Sap lake is lower. Flow goes westward. At low flow after monsoon season, the Mekong goes back to being lower than the Tonle Sap, and flow eastward resumes. It's like an immense overflow safety-basin. Plenty of oxbow lakes on seriously meandering rivers do this during flood times; the Tonle Sap is just a huge version, at maybe 100km of 'reversing' section.

At least in this case it's not a purely graphic feature - you about have to have some text to explain it.

Ascension
12-18-2009, 12:51 AM
That's a really cool bit of info.

Meridok
12-31-2009, 07:27 PM
Read through this whole thread and didn't spot this little bit of info elaborated upon in reference to the Canadian lakes system, and other similar ones world-wide:

As noted, the rivers & lakes get pretty crazy because of the glaciation and the (generally) hard surface rock (at least over the Shield area). But another reason is the fact the Hudson Bay drainage system and the other ones around there are quite young, geologically speaking. Young drainage systems tend to be quite chaotic, while older, more established ones are just that: more established, thus more silted (more developed oxbows, etc). So that is another thing to keep in mind when doing lakes - how old is the drainage system?

And to add to the 'anomalies' list: Check out the Reversing Falls (http://www.new-brunswick.net/Saint_John/reversingfalls/reversing.html) in New Brunswick. Water only flows down due to gravity when there isn't another stronger force acting up! :) Admittedly, the Bay of Fundy is something of an anomaly, but it certainly provides a handy explanation if you want something neat like that (imagine the effect if there was a bay like that with a fjord-riddled coast or something?) without a 'magical' explanation.

ETA: I think I meant watershed, not drainage system, but still, basically the same! xP

the-golem
01-21-2010, 11:07 AM
Since we're all on the topic of rivers and such ... Relatives of mine recently went on a Carnival cruise, and one of their stops was Newfoundland. Apparently -- and this is somewhat evenidenced from the photos I was shown -- during high tide a quite extensive portion of the river actually flows "upstream." It seems that the tide rises so high, it just flows backwards. From what they said, you could see the river fighting with itself, and there were all these swirlies and eddies and whatzits.

Gidde
01-21-2010, 12:36 PM
That would be cool to see!

waldronate
01-21-2010, 12:45 PM
Tidal bores are your friend! Just search for that term in any internet video search engine to see what I mean.

Redrobes
01-21-2010, 04:48 PM
Heh yeah, I live here next to the River Severn which is the longest river in UK and that wedge shape bit bottom left dividing England from Wales. It also happens to be the second largest tidal region in the world and has regular bores where a lot of people get out for to watch - most in wet suits...

http://www.youtube.com/watch?v=PtUmLLlm7S0

Not Hawaii I grant you.

arakish
08-22-2010, 04:57 PM
Actually, Niagra Falls was mentioned in that same show.

Apparently Lake Huron and Lake Erie didn't use to be connected. But with the rising of the Lakes caused the water to be forced over the land between the two lakes, which formed the rivers that joined the lakes. The connection between the two occurred 1800 years ago.

Water from the upper lakes flowing into Lake Erie then Lake Ontario caused the water to flow which eventually formed Niagra Falls. So apparently Niagra Falls is relatively "recent" (in geologic time). The show suggested that eventually the water volume flowing over Niagra Falls will increase, though it may be several thousand years before there's any real kind of disasterous change, due to that.

GP

Although not posted to for awhile, I thought I'd add this little tidbit about Niagara Falls.

I also watched a History Channel's show about the Niagara Falls (http://en.wikipedia.org/wiki/Niagara_Falls). One thing mentioned in that show is the fact that the four upper lakes water level will drop by up to the height of the falls 52 meters (167 feet). Of course, this won't happen for about another 12,000 years, and the water won't empty all at once but occur over several years to a couple of decades. That increase of water flow will do a heck of a gouging job.

rmfr

arakish
08-23-2010, 12:21 AM
Finally found this on an old DVD, here is a paper I wrote to a friend about drainage patterns. Maybe this can help some also?

28338

Although a copyright exists within the document, I am releasing it under Creative Commons No Commercial, Share Alike license.

rmfr

RobA
08-23-2010, 01:37 PM
Also like to add the NASA GES geomorphology site. specific to this discussion are the Fluvial Landforms from space (photos plus diagrams):

http://daac.gsfc.nasa.gov/geomorphology/GEO_4/index.shtml


-Rob A>

Daunty
02-03-2011, 05:01 PM
Hi i have a question that confuses me a bit, i was hand drawing a underground dwarven stronghold. on one side of the mountain i have a valley with a river above the ground (between to mountains), i understand that alot of the water will go into that river due to the catchment area. as i have been drawing further and further down into the mountain i thought would i b able to have like a underground lake or would the catchment area of the river stop the lake from filling up. there not right next to eachother but the river is on the side of the mountain and the lake im thinking of will b almost dead center under it. i thought i would ask b4 i actually had a go at drawing it in.

thx for any help and i do apologize if this isnt the right thread/topic to ask.

Ascension
02-03-2011, 05:21 PM
I would assume that you could have an underground lake anywhere you want provided that there is rock preventing them from joining together in a vital area.

MarkusTay
03-15-2011, 02:14 AM
I was looking for some visual aids for describing some terrain to RPG players, and my search was 'Canadian Shield Region'

And I came across This river system. (http://rst.gsfc.nasa.gov/Sect18/mani115.jpg)

I thought you guys might find it interesting. If I saw someone draw that on a map I would think it was very 'unrealistic'. :P

Its with a bunch of other pics in an article on craters, which you can find HERE. (http://rst.gsfc.nasa.gov/Sect18/Sect18_5.html)

Midgardsormr
03-15-2011, 02:50 AM
Very cool! I'd probably call it out, too, if only to get the story behind its formation. I'm sure nobody would put that on a map without a story to go with it.

Ascension
03-15-2011, 05:34 PM
Yeah, that's from a crater. I saw it in one of those science shows that I'm always watching on the Science Channel...I think was called "How the earth was made" and it was in one of the episodes. Might be a different tv series, I can't keep them all straight in my head. Normally you'd think that the crater edges would prevent a ring river but the mound-in-the-middle resulting from the impact was very dense so it eroded very slowly while the edges were closer to normal dirt so they eroded faster. There's a few others like this in Asia and Central America if I remember right.

RobA
03-21-2011, 04:55 PM
I was looking for some visual aids for describing some terrain to RPG players, and my search was 'Canadian Shield Region'

And I came across This river system. (http://rst.gsfc.nasa.gov/Sect18/mani115.jpg)

I thought you guys might find it interesting. If I saw someone draw that on a map I would think it was very 'unrealistic'. :P

Its with a bunch of other pics in an article on craters, which you can find HERE. (http://rst.gsfc.nasa.gov/Sect18/Sect18_5.html)

It's not technically a river, but a lake with a large island ;)

http://en.wikipedia.org/wiki/Manicouagan_crater

You might also like this earth impact crater viewer....http://impact.scaredycatfilms.com/

-Rob A>

Lewas5372
04-12-2011, 09:07 AM
Texas is a bad example of lake formation, unless you have a race of sentient beavers in your fantasy world . All lakes in Texas are artificial save one, Caddo Lake, and we dammed that one for good measure, too. As for crazy forking Texas rivers, they never split after joining up and all flow to the gulf or the Rio Grand then to the gulf. Most of the time when something violates a rule its because of either heavy rainfall/flooding, which will sort itself out quickly, or because man stepped in a messed with things (i.e. the Chicago river flowing the wrong direction)

Redrobes
04-12-2011, 10:49 AM
Absolutely ! This thread is about natural rivers and the long term state of them (and on a non magical earth like planet too). Post flood and tsunami... well almost anything goes. Then in the medium time span there is this braiding and some extreme cases of meandering then longer still you might have oddities from glaciers periodically freezing and thawing in multi decade cycles but generally, in the long term, the idea that rivers don't fork and exit into the sea in one spot holds true. I guess if considered long enough then any river system is dynamic enough that there is no stable state for it but for the maps we make here that's not really applicable.

Ryan K
04-12-2011, 09:32 PM
Texas is a bad example of lake formation, unless you have a race of sentient beavers in your fantasy world.

I read that and I think 'dwarves' ;)

Insufferable Fool
08-12-2011, 10:46 PM
http://en.wikipedia.org/wiki/Stream_capture
Stream Capture (also known as Stream Piracy) is pretty sweet.

-Rob

Extremely relevant example: the artificially-postponed capture of the Mississippi River by the Atchafalaya. http://en.wikipedia.org/wiki/Old_River_Control_Structure

Would make for a pretty decent story in a fantasy setting too; a terrible disaster as a major port dries up. Or else an excuse for extensive ruins of that major port, decades/centuries after the fact.

kiriona
01-19-2012, 01:32 PM
Seems about right. It's worth noting that when rivers do split up high in their courses it's most commonly due to stream capture—which takes a very short amount of time, geologically speaking. Probably the most notable example is the Casiquiare (http://en.wikipedia.org/wiki/Casiquiare) which links the Orinoco and Amazon basins. It was originally a separate river, but has currently migrated far enough to capture the upper Orinoco, which will eventually (ie in a few thousand years or so) drain entirely into the Casiquiare. A bifurcating river is possible, just unlikely. A map with lots of bifurcating rivers needs further explanation (eg the area is full of karstic terrain, the bifurcations are artificial etc)

Otherwise yeah... and I must say it's a relief to see a forum where mapmakers actually keep this in mind instead of just filling their maps with circular rivers and rivers flowing from one sea to another etc ;)

Mixail
03-25-2012, 05:41 AM
Well, I joined just for these tutorials

s0meguy
04-08-2012, 02:32 PM
edit: I'll just make a thread about this because people probably don't look at these stickied threads much.

Question: Soil around rivers tends to be fertile right? So when making maps of fictional areas I always have a tendency to put a bunch of trees next to the rivers, and some forests sometimes, especially in an area where 2 or more rivers are relatively close to each other and lakes because the river is dumping all the soil nutrients there in the lake, so the soil around it would probably be fertile enough to support a forest. I'm always having a hard time over whether the soil around rivers is fertile, and if it is, what kind of vegetation i should put along side it, and also where to put forests in general. I gathered that they are usually next to mountains, because they trap moist air/rainclouds. Any good rules of thumb?

Neorael
04-12-2012, 08:18 PM
I wanted to thank you all. Every part of this topic has something to contribute in the learning of how the hydric sistem operates :D

Midgardsormr
04-13-2012, 01:49 AM
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
06-21-2012, 09:18 AM
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
06-24-2012, 12:05 PM
Go ahead and post it up, pdf collations are always welcome.

Elothan
06-24-2012, 04:27 PM
Go ahead and post it up, pdf collations are always welcome.

Rivers and Lakes
(https://dl.dropboxusercontent.com/u/9091222/Fantasy%20mapping%20tips-Rivers%20and%20lakes.pdf)
I will probably expand on this document with what I learn along the way in relation to mapping :)

necrominog
06-25-2012, 03:59 PM
Was just directed to this thread. Very informative. Thanks!

Now to correct the error of my ways...

-nog

Niedfaru
07-04-2012, 11:01 PM
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
07-05-2012, 02:09 AM
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
07-05-2012, 07:27 AM
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 (http://upload.wikimedia.org/wikipedia/commons/a/a9/Iraq_marshes_1994.jpg) seems to show Iraq breaking almost every river police rule in this thread.

macziggy
08-01-2012, 01:12 PM
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 :)

Redrobes
08-01-2012, 02:37 PM
Yes I believe your right there. Its here:

https://en.wikipedia.org/wiki/Casiquiare_canal

It seems that its on the line of the catchment area between the two rivers and it seems to link to both but it notes in the wiki entry that its mainly from flooding. So it certainly is one of a very small number of natural channels that link two rivers which flow to the oceans at two different places. I suspect tho that given this area is pretty flat then geologically speaking after a short amount of time erosion will channel this water to just one of them. But for now this would indeed be an exception to a general rule. Water cannot gain energy however so at all times this water is flowing downhill but it seems that the lower level of what is considered down oscillates between these two main rivers based on rainfall and flooding.

Good post tho - thanks !

Rivers joining up are not uncommon and a river may bifurcate extensively near to a point of mass drainage like the ocean or a big lake which is a delta. So the Mesopotamian marshes are not so uncommon and not as much of a rule breaker on these "river violations". Again, this is due to sediment carry and flooding oscillating what is the lower level on a fairly flat plane. Am I right in saying that it was thought that the city of Alexandria was built on a plane next to these (or other rivers like these - Nile perhaps ?) and that on a particularly flooded time and with some kind of earthquake then the ground became liquid and the city sunk into it. A river delta is a constantly changing place where I would argue that at a single point in time the river rules apply but over a short time span they change so fast that it appears to violate them.

Midgardsormr
08-09-2012, 12:41 AM
Considering how many cities Alexander founded and named after himself, I would be very surprised if one of them wasn't in the Tigris-Euphrates floodplain. And it also doesn't surprise me that it might have sunk into a marsh; Alexander wasn't the Greatest city planner.

Xanthemann
08-19-2012, 02:52 AM
This is (as you probably know) very informative. Thank you for the info!

Kafei
08-24-2012, 10:47 AM
Would anyone be interested in a tutorial on the morphology of rivers on a macro scale, all related to worldbuilding? Rivertypes (Meander, braided, sinuosity, shape, gradient), types of delta's and coastal features? I would not mind gathering all the information from this topic and putting it into a single .PDF file, it's all kinda scattered right now.

anstett
08-24-2012, 01:29 PM
I think that lots of people would be interested in such a resource.

A simple one page "do's and don't's " and then additional detail for those that want it would be a great way for beginning mappers or world creators to learn some good info.

BOB

Kafei
08-25-2012, 08:12 AM
http://www.mediafire.com/?e6t9adhdarhocme

Here you go, I'll add all the other things posted in this topic later.

waldronate
08-26-2012, 03:38 AM
I'd love to see the document, but I'm not much in the mood to install things from third party sites. Any chance that it could be directly uploaded here, instead?

rahta
08-26-2012, 04:30 AM
I already downloaded it (i am not really the cautious type, heehe ""XD) and it is a really useful document. Like this thread itself. I hope it is not a problem if i upload it here for you, Kafei. It will be just much faster for the others. Here ya guys go.

Schwarzkreuz
08-26-2012, 06:11 AM
Oh thats realy great, thanks for the afford (+Rep)

vorropohaiah
08-26-2012, 07:44 AM
this seems quite handy!

Realmwright
08-26-2012, 02:56 PM
All very good points. I remember only a little from jr high Earth Science, but I remember lots from college geography courses. The bottom line is that, as our illustrious post leader pointed out, water must flow downhill and/or gather in lowland areas. It is very good advice to figure your terrain features and mountains BEFORE placing rivers because I tend to think you only get a say in one or the other. Mountains tell you where rivers can be, and vice versa. As for the bit about water tables and springs, it makes sense, but it's also pretty deep (no pun intended). If most other mappers are like me they get a blank outline and then stare at it dumbfounded about what to do next. Great, I have a shape of the landmass......now what? Figuring out the surface terrain is enough of a task without trying to incorporate soil density.

Caenwyr
09-17-2012, 11:26 AM
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 (http://www.cartographersguild.com/showthread.php?20001-Foam-Carthography).

Many thanks in advance!

Redrobes
09-17-2012, 11:46 AM
Hi Caenwyr, that software was my own and its unreleased. Its a total PITA to use and it has no GUI so it would be a problem releasing it. However, there is Wilbur which is written by another member here and the author of Fractal Terrains. Wilbur is free and downloadable and also calculates river path predictions based on similar criteria to my app simulation. So check this link out:

http://www.ridgenet.net/~jslayton/wilbur.html

Midgardsormr
04-11-2013, 12:30 AM
I found an interesting factoid that probably only the most ardent of us will apply: The ratio between the length of a meandering river and the length of a line drawn from its source to its mouth approximates pi (3.14159…).

Pi -- from Wolfram MathWorld (http://mathworld.wolfram.com/Pi.html)

RobA
04-11-2013, 01:47 PM
I found an interesting factoid

Sounds more like a "fractoid"

-Rob (not very punny) A>

Gumboot
05-22-2013, 01:07 AM
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.


You're quite right, although trees don't grow where rivers are, as such. Rather both trees and rivers tend to end up in areas of high rainfall. Water in a river isn't much use to a tree, because trees don't grow in rivers. But rivers tend to flow where there's more rainfall. Trees get their water mostly from rainwater falling on the ground where they're standing. The water that isn't absorbed by trees ends up in rivers.

Generally speaking:

Higher rainfall = more trees + more rivers
Lower rainfall = less trees + less rivers

Hai-Etlik
05-22-2013, 03:31 AM
You're quite right, although trees don't grow where rivers are, as such. Rather both trees and rivers tend to end up in areas of high rainfall. Water in a river isn't much use to a tree, because trees don't grow in rivers. But rivers tend to flow where there's more rainfall. Trees get their water mostly from rainwater falling on the ground where they're standing. The water that isn't absorbed by trees ends up in rivers.

Generally speaking:

Higher rainfall = more trees + more rivers
Lower rainfall = less trees + less rivers

Actually on the great plains it is the rivers directly allowing the trees to grow, they aggregate the water, and bring in water from rainier areas, which allows the trees to grow in the river valleys despite not having any more rain than the surrounding plains.

mssandhu
06-17-2013, 03:57 PM
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!)

Korash
06-23-2013, 07:54 PM
You might want to look at one of RobA's scripts here (http://www.cartographersguild.com/tutorials-how/3011-award-winner-tapered-rivers-gimp.html#post32810). I am not sure how it fits into 2.8 but might be worth a try. Let us know how it works out.

Midgardsormr
06-24-2013, 10:22 PM
I had a thought the other day concerning the interface between rivers and seas, so I thought I'd bring it up here. We have discussed delta formation in fairly great depth, but there hasn't been a more general conversation about how rivers affect coastlines.

To start the discussion off, we know that as a river nears the sea and loses momentum that it can drop silt, which is what causes a delta to form. Usually, the delta will extend the coastline outward, as can be seen around the Mississippi Delta and the Nile. In contrast, other rivers may form an estuary, where the river erodes the coastline away, allowing the sea to move further and further inland. Because the estuary is filled with a mixture of seawater and river water, it usually has lower salinity than the ocean, but higher than the river. Many deltas also have this feature, and in both cases, the water level and level of salinity may be dependent on the tide. In some cases, a river ending in an estuary may actually run backward at high tide, as pressure from the narrowing channel temporarily forces the water to run uphill.

Are there any other interesting coastal formations caused by rivers? Have I got anything wrong there?

Redrobes
08-12-2013, 08:37 PM
Posted on reddit's earth porn. A triple water shed point which is quite rare.

"Triple Divide Peak, Montana, USA. The peak shed water to the Pacific, Atlantic and Arctic Oceans"
http://i.imgur.com/IMs8Q.jpg

Trismegistus
09-23-2013, 02:04 PM
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 (http://en.wikipedia.org/wiki/Endorheic). I live in an endorheic basin. I like to think in terms of 'watersheds (http://en.wikipedia.org/wiki/Water_basin),' 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 (http://en.wikipedia.org/wiki/River_morphology) 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 (http://en.wikipedia.org/wiki/River_Thames) (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 (http://en.wikipedia.org/wiki/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.

RonnyRulz
10-13-2013, 12:13 AM
We have had so much talk on this subject and so many maps fail this point that there is a River Police badge now for officers of the CGuild to catch miscreants in the process of making a map with duff rivers.

We have stated many times that water flows down hill and others, especially Waldronate, have given a list of points that must be true for water in a non magical and natural terrain and yet we still have those maps coming in.
...
...
...


THANK YOU!

This was one of the best written, easiest to understand articles I've ever read. Especially considering the complex science of river formation, I cannot believe how easy this was to learn thanks to the author's ability to write so well, concise but detailed.

Knowing how rivers form IRL and the Do's and Dont's of the river police, actually made it EASIER to add my rivers in my map.
It would have been a headache to just randomly place them around the map, and very hard to look natural.

Instead, it was easy! So easy, and on my FIRST attempt they looked professional!

I cannot thank you enough for this article.

Valhall
11-06-2013, 07:55 AM
Very interesting post. I always thing about how to place rivers in my maps and sometime its a bit crazy how y do it. Now i know how to do it. Thanks for the post ;)

Duke Ironfist
03-10-2014, 11:11 AM
Yes, being Canadian as well, I found the statement that lakes are rare interesting indeed. Your point of Northern Glaciation is right on the money!

Hai-Etlik
03-13-2014, 10:15 PM
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.

The definition of "endorheic" is that the basin is closed, not that is part of that list. So it's not "by definition". If an outlet formed from the Caspian to the Black Sea, the Caspian would cease to be endorheic. As you point out a little later, the Saint Lawrence drains the Great Lakes into the Atlantic, so the Great Lakes watershed is not endorheic. Lake Baikal also has an outlet in the Angara River, a tributary of the Yenisei River, which flows into the Arctic Ocean.

waldronate
03-14-2014, 02:24 AM
Unrelated, but rivery: Time lapse of a river changing course / JustGIF - Gifs, animations, lols, fails, memes, trolling (http://justgif.com/262237/time-lapse-of-a-river-changing-course)

JefBT
04-07-2014, 11:35 AM
After reading all this I came to a conclusion to make realistic river and lakes:

Follow the 3 steps to have regular rivers.

If you want to make exceptions, use the google maps/earth (or another real world map) and look for something that is what you are looking for, and you probably find your exception hidden somewere in our world.

Nice thread

MarkusTay
04-23-2014, 01:16 PM
Something I came across yesterday. (http://sploid.gizmodo.com/this-creek-divides-the-us-connecting-the-atlantic-and-p-1565867365?utm_campaign)

Just to prove that for every rule, there are exceptions. One of the biggest mistakes (supposedly) I come across in fantasy maps is a single river dividing and going off to two different seas. Apparently, it IS possible.

Azelor
04-23-2014, 03:24 PM
I guess it's possible but it's not common and it's only a little stream of water. I don't know if it would be the same with a large river.

Redrobes
04-23-2014, 04:55 PM
Yes there are a few. See https://en.wikipedia.org/wiki/Bifurcation_%28river%29 and also Isa Lake - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Isa_Lake). But note that in all of the cases they are on geologically unstable places. Specifically for the Teton Two Ocean Pass its on the North America Continental Divide and the Isa is at Yellowstone. These places will only exist temporarily and in a few hundred years or perhaps a little more but trifling geologically, one side will dominate the flow. There are more that normally only flow in one route but during floods will cause the flow to exceed the capacity of one side and will then have two paths to different places. It is a certainty that at the very edge of the catchment basin where it meets its neighboring catchment basin then a drop of water is critically unstable in its route to the sea. There would exist many places where the flow is a merest trickle and then bifurcates but the more considerable the flow of water the harder it would become to show the bifurcation. A larger flow would erode one side faster than a trickle over the flat ground on the edge of catchments.

MarkusTay
04-24-2014, 12:41 PM
I understand all that.

But in my mind, something that I had (for awhile) considered 'impossible' is merely implausible... and that's a big difference. Especially when creating fantasy maps.

waldronate
04-24-2014, 05:03 PM
In fantasy, physics need not apply. A DM I once knew decided that the big mountain in the center of the island should disappear, leaving a big hole. The large river that had flowed from the mountain to the sea now served as a channel for the sea to flow back into the big hole. Implausible, but possible. And certainly not stable. Ever since the big hole appeared just south of the Sea of Fallen Stars in the Forgotten Realms, I've been waiting for some enterprising gnomes to dig a canal from the sea to the hole and set up a few waterwheels on it. The unintended erosional consequences and migrations due to flooding would be hilarious!

Hai-Etlik
04-24-2014, 06:25 PM
In fantasy, physics need not apply. A DM I once knew decided that the big mountain in the center of the island should disappear, leaving a big hole. The large river that had flowed from the mountain to the sea now served as a channel for the sea to flow back into the big hole. Implausible, but possible. And certainly not stable. Ever since the big hole appeared just south of the Sea of Fallen Stars in the Forgotten Realms, I've been waiting for some enterprising gnomes to dig a canal from the sea to the hole and set up a few waterwheels on it. The unintended erosional consequences and migrations due to flooding would be hilarious!

So, pretty much this: Qattara Depression Project - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Qattara_Depression_Project)

waldronate
04-24-2014, 11:04 PM
Or the one from the Gulf of Aqaba to the Dead Sea, or the one from the Gulf of California to the Salton depression, or the one from the Red Sea into the Afar depression. It's a popular topic. It's also a major ecological disaster for the ever so fragile ecosystems (except for the Salton depression, which has already had that particular disaster). But the Forgotten Realms one is particularly interesting because the hole is very deep and the distance not too far. When the gnomes put their giant hamster wheel-powered excavators to work on a basic canal, accidental erosion could VERY quickly turn it into a miles-wide waterfall unless there is a very solid ridge in the way. It's mostly plains with no particular hills in the way...

Trismegistus
06-15-2014, 02:17 PM
The definition of "endorheic" is that the basin is closed, not that is part of that list. So it's not "by definition". If an outlet formed from the Caspian to the Black Sea, the Caspian would cease to be endorheic. As you point out a little later, the Saint Lawrence drains the Great Lakes into the Atlantic, so the Great Lakes watershed is not endorheic. Lake Baikal also has an outlet in the Angara River, a tributary of the Yenisei River, which flows into the Arctic Ocean.

I didn't know that about Lake Baikal. Thanks for pointing that out. I should have caught myself with the obviously inconsistent statement about the Great Lakes. I've been looking at fractals lately and river systems are sort of like that, especially as you look at them in closer and closer detail.