View Full Version : A Question of Rivers.
06-17-2012, 11:27 PM
First off I want to clarify this by stating I am not a geologist or student of geography, so I don't know much about this topic. That being said, many times when people have posted maps they have been told that their rivers are wrong and that they wouldn't flow this or that way. There seems to be a logic about how rivers should flow. BUT, I was using google maps and looking at the town where I went to school ( Orono, Maine ) and I realized that the rivers there violate some of these "river laws" numerous times.
There may be a logical reason, I don't know, and I'm not trying to start a heated discussion. I'm mainly posting this picture to show that nature doesn't always follow the rules. So perhaps we shouldn't be so quick to tell someone their rivers are wrong.
Anyway, here is the screen capture showing the Penobscot River as it passes thru and around the towns of Orono and Old Town, Maine.
The Red Arrows show the direction of flow as the river heads south to Bangor.
06-18-2012, 12:34 AM
I know nothing about the location. However, I would assume that these paths are not natural but to some extent man made. With dams, locks, gates, channeling, etc., one can make water do almost anything. It usually keeps doing it as long as these channeling structures are maintained. Once they fall apart, the water usually starts reverting back to a natural path, although not necessarily the original path. Here in Europe, the Rhine-Main-Danube canal even flows across watersheds. Ditto for the canal that cuts Scotland in two, going up from one coast and then back down to another.
But remember please: I am not a member of the river police!
06-18-2012, 01:08 AM
There are several dams, but no locks, gates, or channeling that I know of. I think the primary waterflows are all natural. But I don't know that for sure.
06-18-2012, 01:20 AM
Don't worry Bogie, I'm sure one of the geologist types will have a clear answer soon. It does look pretty wild though. I would think it's some kind of man made engineering that is forcing or keeping things in check there but like you guys, I'm no expert.
06-18-2012, 01:57 AM
Oy! Indeed, that's a convoluted set of stream directions. And over a small stretch of territory, not terribly rare. Figure if the land is flat enough, another two or six or ten feet of depth would cause an outright lake, from leftmost bank to rightmost bank. Then imagine the water dropping a bit and the very slightly higher land happening to be in the middle of the whole area splitting the watercourse into two, or ten. Which way the actual movement of the water occurs may be as much a matter of current striking the basin >here< and sloshing >thattaway< and etc. -- like currents within a clear, wide lake can flow this way and that according to entry of streams, bottom topography, winds, and the like.
Note though that the streams in your example do rejoin - as such, it's more a case of 'stream threading' than 'stream divergence'. Such islands or systems of islands can stretch a long way. If it's happening near the entry point of a larger body of water, it's a delta, and technically is divergent. What you *don't* see is a river forking mid-way across a county or nation, choosing to flow into widely disparate oceans or lake basins. Note the scale - how long are these several islands you show? Usually they're no more than a hundred yards or a mile or three long. Fair enough: there's such an island maybe sixty miles long in Argentina (between Rosario and Buenos Aires) - still, think of it as a bit of river that swells to some fifteen miles wide, happening to have an island 14.5 miles wide in midstream.
The absolutely delicious extreme example is the river that flows out of Cambodia... except when the river it flows INTO rises by just a foot or two in flood season, whereupon said tributary actually reverses flow and actually runs back INTO Cambodia. All so very flat that a difference of a foot here or there drastically shifts the local stream pattern. Look at the Suudd in central Sudan - nastiest swamp in Africa; stopped upstream exploration on the Nile for half of *forever*. It shifts and twists and channels open and close and generally act unreliable and sneaky. I bet that a honkin' big rainfall like a prolonged nor'easter coming ashore will temporarily alter the pattern you show in the example --- a serious flood like happens on the Mississippi, Missouri, etc making *permanent* shifts (for values of "permanent").
So yeah - that example bends the rules; such rules being more rules-of-thumb than laws. What one ought to avoid in fantasy topography construction is egregious flaunting of the river-layout-plausibility-suggestions :-) by making rivers that divide and rejoin across great swaths of non-flat territory, and ones that run 'downhill' in more than one direction. Indeed, done right, showing threading and meandering and suchlike big complex-flow island-networks can be a huge indicator that the terrain is flat-flat-flat, and borders on being swamp/bog/marsh/bayou.
Mark's guess than man's interference could be at play is another possibility. As meanders shift a riverside port away from the main channel, locals may dredge and dike and meddle to get the nice profitable barges and paddlewheelers back in town. Canals need not be ruler-straight; indeed long ones follow terrain (sidehill instead of downhill, if they're trying to avoid locks) and can work up into the kind of network of his Rhine-Main-Danube area, or the tangle the Rhine & Meuse make when they hit the Netherlands.
Almost any rule of laying out topography and hydrography can be 'broken' , just at a cost of explanations needed to keep plausibility. A tenet of storytelling is that one does not include details that detract from the story itself - but if odd, unique, strange details actually contribute to the story your map tells, then go for it !
06-18-2012, 02:02 AM
Is it possible that some of those places the water is flowing around are a lot denser stone, and the water is cutting through some narrow softer rock around/in between? Perhaps the avenues are too small to accomodate all the water, so it splits apart until it can work its way back to a big enough channel through the stone.
I am not a geologist either.
That *might* happen, but you have to keep in mind that river flow rates vary depending on the season and thus evaporation and precipitation. Smaller channels would only fill up when you had a lot of rain over a short period. If you look at alpine rivers, especially when they hit the lowlands, they tend to start threading in their streams and creating vast gravel beds with the main streams shifting around pretty swiftly - even a single massive precipitation event (MPE :P) can radically change the look of such a river - not to mention that it can simply redirect during floods (e.g. lots of rivers on the Po plain have shifted around quite a bit from Roman times to now).
06-18-2012, 04:06 AM
Two points: This map covers a very small area and has no fewer than five dams/falls on it. The dams/falls are marked in blue on the attached image. Most of the comments about river flow are over areas of dozens or hundreds of miles, assume no modifications of the river flow by artificial means, and assume roughly stable configurations from a geological perspective.
06-18-2012, 09:23 AM
yup even just dams can do that.. especially on flat lands... in my area we have a city called peterborough.. they installed an electric dam back in the day, and it affected rivers and lakes for up to 100km upstream... it would quadruple a lakes size, reroute, split up or even remove a river all together... it's amazing what a fairly small change can do...
I worked for a natural heritage conservancy there, and i worked on a "before and after" map, using old maps from before the dam was created and maps from now... the difference in the overall river/lake layout was quite easy to see.
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