Posted on March 19 2019
- There are so few things we can count on 100 percent. Certainly the doings of humankind are rife with failure, deception, and disappointment. Nature provides us with more reliable behaviors, so much so that when we get unexpected results, we are generally flabbergasted. One thing you ought to be able to be certain of is that water will always flow downhill—it seeks the lowest level it can reach because gravity never sleeps. There are, however, a few interesting exceptions to what would seem to be an immutable condition. On a really tiny scale, water defies gravity around the edge of every glass of liquid beverage you pour. Capillary attraction pulls the water slightly up the side of the glass because water molecules like to stick to each other (cohesion), and to other things (adhesion). It climbs a bit up the container wall in a little rise called a meniscus. The layer of water at the surface, where it meets the air, holds together with more strength because the water molecules there have no molecules above them with which to share their bonding forces. Hence, they grip those next to them more strongly, which creates a sort of skin on the surface called surface tension. The meniscus can only climb so high up the glass wall, because surface tension, and of course gravity, hold it back.
That’s one of the tiniest expressions of anti-gravity water that you may easily notice. It’s also going on a little less visibly inside of plants, where capillary attraction and the stickiness of water molecules, plus the siphon effect, pull water up tiny tubes all the way to leaves far off the ground. But let’s go macro—wrong-way flow can be seen in some fairly large-scale scenes too. One of them has a human origin, because humans are just so good at messing with natural processes, at least temporarily. In California’s Great Central Valley, the San Joaquin River flows into the Sacramento-San Joaquin Delta on its way toward San Francisco Bay. Channels of that river, the Old and Middle rivers, can actually have their flows reversed by powerful pumps which suck water into canals headed to thirsty Southern California. The reversal confuses migrating fish and sends some to their death in pump machinery, despite screens meant to save them. The flow-reversing pumping is sometimes curtailed to avoid the destruction of the rare delta smelt, and various salmon species. If a huge new water tunnel plan is built, the problem of reverse flows might go away, but that’s a whole ‘nother story.
Nature can outdo humans in upsetting the “natural” scheme of things. Heavy rain in a mountain setting can send so much water down a main channel that smaller tributary creeks run backward for a distance, pushed upstream by the high volume. Nature does even more impressive displays of backward water movement during certain tidal conditions. As the Geo-Joint has noted in the past, rivers such as the Amazon, the Ganges, the Severn and many others feature not only a flow reversal at particularly high tides, but also surfable waves of some size. The Bay of Fundy’s deep tides push water and waves upstream, and completely cover and make temporarily navigable some normally impassable rapids on the Saint John River. Another example of rivers doing an about-face can occur during in the storm surge accompanying powerful hurricanes. Even the Mighty Mississippi has been turned back on itself, if only for something less than a day. Hurricanes Isaac in 2012 and Katrina in 2005 had such an effect. The story is told that the Mississippi once saw itself going the wrong way for an entirely different reason—the massive New Madrid earthquake of 1811. Uplift from that quake may have caused parts of the river to reverse flow, or eyewitnesses may have been fooled by seismic waves moving north in the water, which might have created an illusion. But surely an earthquake properly placed could turn a river around.
Optical illusion plays a part in local lore in some places, where rivers are said to flow upstream along roads that parallel them, especially in mountain streams. If there is a slight upward gradient to the road while the flow of the nearby creek is following a moderate slope downhill, it can seem as though the river is climbing the rise along with the car you’re in, or that the water is going uphill as the car descends. This is all a function of human perception and roadbed construction, which for reasons entirely unrelated to water flow, may have a gradient slightly opposite that of the creekbed.
Illusion, or perhaps delusion, leads some people to think that rivers such as the Nile in Egypt, the Mackenzie in Canada, or the Lena and the Yenisey in Russia must defy gravity because they flow to the north. In this country, it may be the big, southward-heading Mississippi that tends to ingrain the idea that somehow “south” means “downhill.” Up, down, east, west—they’re all human mapping constructs of little interest to nature. Some have posited that because the mouths of rivers that flow south for a long distance are farther from the center of the earth than their headwaters (due to the oblate spheroid, or squished-sphere shape of the Earth), that these rivers flow “uphill.” Of course, normal water flow is dictated by elevation and gravity, which act upon water locally as it seeks the easiest path to the lowest place, which is usually the sea. Any centrifugal force stretching the girth of the Earth is pushing the water toward the equator as well, so with that force and gravity in balance, water is still seeking the lowest point it can reach, not caring how far away it is from the center of the planet. Sorry if that got a little convoluted. Suffice it to say that water, left to its own devices, moves like water at any point on Earth.
Oh, but under the Earth things can get weird again! An underground river, if it fills its conduit, can flow in an upward direction if it then descends to a lower elevation, due to the siphon effect, like the water in the trap under your sink. But the flow must be solid, or air gaps will break the suction, and the water will fall back to its low points. And there’s another example you can’t see—rivers between the lakes that underlie the massive Antarctic ice sheet. Yes, through compressional heating or subsurface heat sources, there are pools of melted ice at the base rock, some quite large, and they are often connected by streams and rivers flowing along the rock deep below the ice. Under the staggering pressure of the overlying ice, water can be forced uphill through these channels over buried, mountainous ridges aligned perpendicular to the ice flow. At 1,728 pounds to the cubic yard of water, think of the energy that takes. Fighting gravity to make water move upward in a big way is just exhausting—I think I’d rather let gravity do its thing, and float down a lazy river.
Just can’t wait to catch a wave on the Severn River? Don’t forget to pack your wetsuit, and let Michelin guide your travels in Wales and South West England. Maps.com can provide the map, but sorry, not the wetsuit.
caption: Climbing the walls—water fights gravity and forms a meniscus by use of adhesion and cohesion.
source: Wikimedia Commons: PRHaney (CC by SA 3.0 Unported)
caption: Water climbs trees, too. Sticky water gets siphoned up from the roots and eventually goes out the leaves or needles, sometimes hundreds of feet up.
source: Picryl: Unknown (Public domain)
caption: The Sacramento-San Joaquin Delta. In channels just west of Stockton, pumps can force the natural flow to reverse.
source: Wikimedia Commons: Matthew Trump (CC by SA 3.0 Unported)
caption: Tidal bores running upriver can create surfable waves. Here, the Severn River in England provides the locals with a little fun.
source: Wikimedia Commons: Forester2009 (CC by SA 3.0 Unported)
caption: Russia’s big eastern rivers flow north to the Arctic Sea, but they all flow downhill under the force of gravity.
source: Wikimedia Commons: Kmusser (CC by SA 4.0 International)
caption: The Nile runs north too, to its rich delta on the Mediterranean Sea.
source: Pixabay: unknown (CC 0)
caption: Under-ice lakes, like Lake Vostok in Antarctica, can move water around, even uphill, under the weight of the thick ice sheet.
source: Flickr: Zina Deretsky / NSF (Public domain)
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