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Thread: How to get your rivers in the right place

  1. #51
      Redrobes is offline
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    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.

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    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.

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    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.

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      RobA is offline
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    More interesting stuff. I came across this image at Wikipedia (image has been released to public domain):

    How to get your rivers in the right place-ocean_drainage.png

    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):

    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>

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      Ascension is offline
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    Interesting. I'd like to see rivers superimposed on top to see how that comes out.
    If the radiance of a thousand suns was to burst at once into the sky, that would be like the splendor of the Mighty One...I am become Death, the Shatterer of worlds.
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      rdanhenry is offline
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    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.

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      Redrobes is offline
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    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.

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    Another unusual situation you could use for a really special place is a bidirectional river. The one I can think of, the Tonle 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.

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      Ascension is offline
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    That's a really cool bit of info.
    If the radiance of a thousand suns was to burst at once into the sky, that would be like the splendor of the Mighty One...I am become Death, the Shatterer of worlds.
    -J. Robert Oppenheimer (father of the atom bomb) alluding to The Bhagavad Gita (Chapter 11, Verse 32)


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    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 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
    Last edited by Meridok; 01-01-2010 at 10:34 AM. Reason: Terminology!Fail

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