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Thread: The worst river violations ever...

  1. #31
    Guild Artisan Juggernaut1981's Avatar
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    Quote Originally Posted by Gamerprinter View Post
    OK, Juggernaut, have some REP for that bit science on rivers!

    My curious question now regards the Yucatan Peninsula, and the Island of Cozomel. I've been to Cancun, Mexico, on vacation a few years ago, having recently (at the time) learning about the propensity of underwater rivers in southern Mexico. The island of Cozomel (largest island off Mexican coast, very near Cancun.

    Most of the Yucatan is extremely flat, but there are almost no surface rivers there. Sinkholes everywhere. Underground rivers everywhere.

    I visited a "park" that contained a sinkhole right near the coast, about a half mile away from the sea. Fresh water rose from the sinkhole and formed a short surface river called a "Ria" that reached the sea.

    Cozomel is really not that big, yet underground rivers course meandering around the reaching the sea.about 5 meters under the surface.

    I've always wondered about the science regarding that... Can anyone answer, Juggie or Waldronate?? It seems almost bizzare.

    GP
    GP> Thinking about this one... trying to nut the sucker out and I keep coming back to some stuff that is hard to explain but easy to demonstrate.

    Everything has a property called "surface energy" (it's basically the energy required to make surface area)...

    If you drop a liquid on a surface (i.e. glass, the kitchen bench, a sink) it reshapes itself to minimise its surface (because more surface = more energy) and the universe likes to minimise energy.

    Why does this matter?
    Experiment: Get a glass of water, stick a dishcloth in it, drape the dishcloth over the edge of the glass and into the sink. Do the same with another glass but use a NORMAL cloth (any old boring bit of tight-weave fabric)

    Expected results: Water climbs the cloth, over the edge of the glass and down the sink. (Note: if you use hot water, it should do it faster). The dishcloth glass should be more empty than the "normal cloth" after say 1 hour.

    How the cheese does this relate to sinkholes and the Yucatan?
    The ocean is your "sink". The water source is your glass. The two cloths represent the different kinds of land.

    Water likes touching water, but it also hates having lots of surface. In the tight-weave cloth you reduce the surface (by making it touch the cloth) BUT more water is touching cloth which it doesn't like much. There is also no nice smooth "water highway" through the cloth. Any water has to move around in a lot of directions to get around the threads.

    In the dishcloth, there are lots of nice holes and spaces. Holes = water touching water which is good. Cloth = less surface which is good. Loose weave = clear paths to the other end of the cloth. Hence the water should move faster.

    SO back to the Yucatan. Given the options: make a river versus "flow through this swiss-cheese rock stuff" the one that has the least energy involved is the "swiss-cheese rock" AND because there is less energy spent on surfaces, more energy can be spent on moving and hence it is a faster path making sure it meets the requirements of the river police.

  2. #32
      Tiana is offline
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    Wow. Just... wow. I admit I cracked up a bit on the original posted map but the thread was a great read, full of awesome information on rivers and really helps me with my issues with them.

    I do like the cloth/glass explanation, it does help make sense of that theory.

  3. #33
      rdanhenry is offline
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    Does anyone know why these kind of errors are so common? I look back over my old maps, some done as a child (ten, if not earlier) and even when my spelling is terrible and my drawing crude(r than now), the worst things I kind find are an inland lake with no outflow that I think I hadn't planned on being salt water and perhaps a tendency (that has not left) to somewhat exaggerate the meandering of my rivers. Is it just people trying to make maps without any real familiarity with them or something else? I'm inclined to think there is more involved, since these errors seem so common, while I am not seeing such frequent, obvious errors in other factors.

  4. #34
      Ascension is offline
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    My thought is that people just draw maps from old memories and don't really think about it. Memory is often wrong, ask anyone in law enforcement. They get the idea of squiggly meandering rivers with branches but don't even think about rivers joining up to form bigger rivers so they split 'em. They get the idea of a river delta but don't think about it being close to the coast so they start their deltas about 1000 miles upstream. They get the idea of rivers going into lakes but don't think about the lake having to drain...they know about the Great Lakes but forget about the St. Lawrence seaway. When they do think about drain they don't know about one outflow so they put in a bunch...so this is more technical and less common-sense. By and large, people just do and don't bother with the thinking part...that seems to require too much effort, and while that is good for some things (being instinctual is a great boon for say an athlete or a lothario) it is not so good for other things (like physics and medicine). But, that's why we're here...people who want to learn do so and they come here to do it.
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    Maybe they just didn't pay attention in Geography?


    (I'm pleased to say that my GCSE Geography project was all about a river - nothing like actually studying the real thing!)

  6. #36
    Guild Artisan Juggernaut1981's Avatar
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    Expected results: Water climbs the cloth, over the edge of the glass and down the sink. (Note: if you use hot water, it should do it faster). The dishcloth glass should be more empty than the "normal cloth" after say 1 hour.
    Just a side-note for the science inclined amongst us... the REAL fun is observing the water "climbing" the glass when the surface tension/energy minimisation makes it better for the water to climb to the cloth when the cloth isn't touching the water directly than it is to stay where it is.

    This is similar to the phenomenon of "super-fluidity" found when you get liquid helium. The end result is the liquid helium running up the sides of a container to drop onto the floor of the cooling-chamber. I've forgotten how far it will climb, but for <5mL of liquid more than about 10cm is HUUUGE. (Points further questions on super-cooled super-fluid helium to our resident CERN-Nerd)
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  7. #37
      Meridius is offline
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    Hopefully I can add to some understanding of rivers for the downstream part. My knowledge mostly comes from the Dutch situation.

    The most important words for rivers in mountain-like terrain is erosion. Most people know that. Sedimentation is however the word for low-land rivers. Sediment (=soil and tiny rock fragments) is being eroded away by large rivers. However, not all that sediment disappears into the sea.

    In low-land, rivers start to slow down, they get a bit lazy. And because this slower flow-rate (less relief) the heaviest sediments start to sink. Particularly when a river overflows it's banks and retreats again. This water on the banks comes to a complete stop. ALL sediment starts to sink down, and the water eventually drains. The banks become 'higher ground'. If this happens enough times, the rivers main stream will get choked off, and the main stream will bend off around the 'tight spot'. The water in the 'old' river will slow down, and drop more sediment. Eventually the old river will dry up completely.

    Now, even though all this sediment rained down on the upstream part of the low-lands, once the river drains into the sea, there's still a lot of sediment in it. This tends to fall down close to the river. Basically the same thing happens close to shore as it did inland. The river throws down sediment, and land starts to rise. Once formed, the river will flow around here. Eventually, delta's come into being. Because of this process, as long as the river flows the delta will keep moving into the sea (SLOWLY), and branches on the main river in the OLD part of the delta will appear as major rivers branching off.

    Everything in geology is dynamic, it only moves slower than our lives. For things like geology you need to put away your human time-perception, and switch to one where 500 years is 'a short time'.

    Now, all this would be fairly simple if we didn't exist. Rivers follow their own rules, but humans can use those rules. By carving out a channel, a river is easily persuaded to flow into another river. This happens mostly around Delta's I guess, but it makes the situation a bit more complicated. Man, likes having a boat. But man also likes his home. He would also like to have his boat close by his home. Now this is fine, if only the damned river didn't move off... So man will ensure his access to the river by either guiding the river, or by digging channels. This will make us cartographers completely confused about what part of a river is man-made (or man influenced) and what part not. Since our ancestors didn't really care about perfectly straight waterways. Some waterways follow already existing low points in the landscape. Making them look quite natural.

    To name a few rules:
    - GENERALLY rivers only join. They don't separate (delta's are the exception).
    - Rivers flow to somewhere, this may be a lake (which may, or may not drain into another (or the same) river, but this is usually the sea.
    - Rivers flow faster upstream than downstream.
    - In delta's weird stuff can happen, like rivers branching off into two smaller rivers, only to flow into another river, or another earlier branch. As a rule of thumb, delta's are quite big if they extend about 100 km (about 60 miles) inland. Generally the bigger the river, the bigger the delta.
    - Meandering (squigglyness) takes place DOWNSTREAM rather than upstream. The slower a river flows, the more it meanders. Upstream where it flows faster, it usually is much more 'straight'. To get a good feel, go to Google earth/maps, and follow some different rivers in their flow. You'll get a good feel eventually. It isn't really straight what I mean, but you'll see the difference.
    - Don't forget, unless you build a planet without intelligent life, a river will be influenced by intelligent species. As a rule of thumb, if a civilization has bigger ships, it will more actively influence it's rivers. And with 'bigger ships' I mean bigger than a canoe. Draft-ships (ships being pulled by horses) for example. In 'modern' societies (industrial revolution and later) this process only expands. There however will always be people who leave the river as is. Once again, I'm basing this mainly off the Rhine.
    - Two or more rivers can share a single delta.
    - In more local maps depicting a river delta, rivers CAN and WILL branch off and join together again.
    - River islands can be natural, or man-made (channelized river).
    - Rivers don't flow from one ocean to another.

    Basically, the mentioned map is a fine example of how it's done wrong. I doubt it was made this way for this purpose, but showing how it's not supposed to be done is a good way of teaching people

  8. #38
    Community Leader Facebook Connected delgondahntelius's Avatar
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    As to the question on in-house posts referring to river violations and general guidelines on how to map rivers, I thought I'd point to my own tutorial where I touch the subject briefly
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  9. #39
      su_liam is offline
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    In reality, rivers flow faster downstream than upstream. Try standing in the Mississippi in northern Louisiana. The land is flat and has been for some time, but that water is hauling ass. And it will haul yours out to sea if you're not careful. It's so deep that it looks sedate. That's just because it isn't AS turbulent. I almost said, "it isn't turbulent," but my fluvial geomorphology teacher would have knocked my block off if she knew I had said that.

    Give a river a bit of time(and in geological terms, rivers are quick actors: a few centuries can bring big changes, a millennium or two can change the whole gorram river) and it will build a floodplain way up in the mountains and start meandering across it.

    As to time scale, let's just say that using rivers to define borders can lead to headaches. While geologically 500 years is a terribly short time, for a lot of fluvial processes it can be quite awhile. There are borders between my home county and neighboring counties that have been complicated by river movements since reliable maps have been in place. In Oregon. There are significant pieces of Lane county that were on the west side of the Willamette River less than two centuries ago that are now high and dry and on the opposite bank! Mostly folks in Lane county aren't shooting at people in Linn county over border disputes. Now look

    All deltas don't empty into the ocean. Rivers sometimes split into deltas leading into lakes, and rivers often form deltas at confluence points.

    Intelligent life is a huge wildcard. Rivers are sensitive beasts: they connect everything and everything is connected to them. My current watersheds teacher just published a paper about the effects of roads on the evolution of rivers. Dams are huge. Not just in the big flooded area upstream, but by interfering with the natural flood/drought cycle of the downstream reach.

    People like having homes near their boats. True, they don't like the river moving away, but they cry like babies if the river moves into their living rooms. They also tend to do things that make life lucrative for lawyers.

    Don't get me started on irrigation. Look at the mouth of the Colorado... if you have a strong stomach.

    A personal fascination of mine is anastomosing rivers. Look them up. They kind of look like braided streams, but with some significant differences. Braided streams tend to occur on fairly steep slopes(usually with steeper slopes close upstream), anastomosing streams occur in really flat low-energy areas. The bars and islands generated by braided streams usually have fairly low non-climax vegetation, and they are ephemeral things, typically inundated and removed by the annual flood cycle to be replaced by new and different bars. They are below bankful elevation, being basically high points in the streambed. The islands between the branches of an anastomosing reach are usually covered with mature climax vegetation, often forests. The islands in the floodplain of an anastomosing stream are fairly permanent affairs, typically only being flooded on multiyear frequencies and usually surviving several floods with only relatively minor modifications to their size and shape. The islands associated with an anastomosing reach are above bankful elevation and should be considered as part of a segmented floodplain. Also the braided stream has a shallow and wide profile with fairly weak bank material(often pretty similar to the bed material). The anastomosing stream has deep-narrow channels and resistant banks. Okay these are a bit of an obsession with me.

    Oh yeah, sometimes rivers flow nowhere in particular and just dry up. Clearly more of a deserty thing and usually seen more with intermittent or occasional streams. Also... looks nasty on a map.

  10. #40
      Meridius is offline
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    Guess I took in a bit too much of the home-situation. The rivers here really don't 'haul ass'. It's perfectly fine to go against the flow in a rowing boat. Try that upstream... But I guess turbulence was more of the word I should have used.

    I should have added that MOST of my knowledge stems from living in a country that was CREATED by rivers. Without rivers, no Netherlands. WHERE a river flows makes major difference.

    Another thing to remember is that you probably tend to look at a much larger portion of the 'downstream' portion of the river. The US, and most other countries, are HUGE compared to the Netherlands. The Rhine delta IS the Netherlands. So if I'm talking about a river, I'm basically talking about it's delta.

    But I definitely wouldn't say rivers flow faster downstream than upstream. I personally never heard of the opposite, I guess it depends on the river, and that also makes me at fault for stating the opposite. In any case, good point! It proves rivers do different stuff depending on where they flow.

    It also makes perfectly clear why rivers are so tough to understand. Einstein once said sedimentation of rivers is so complex that he couldn't understand his son would even try... I think rivers are pretty complex as a whole.

    About intelligent life. Yes, people cry foul when the river flows in... but it happens. And people still live there. And will stay living there... the same with volcanoes and tidal marshes.

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