Impacts of an Extra-Fast River

[Devor]

Help me out everyone,

I've got this idea for my setting that the river, maybe just for thirty minutes a day, can be sped up to hit speeds of 30 mph, and that a ship could ride that current from the source of the river out to the ocean or to any stop along the way.

But how do I do it and what are some of the implications that I maybe haven't thought of?

The most obvious problem is that it takes a lot of extra water. I was thinking the water would come from a massive natural geyser in the mountains, surrounded by a system of dams that would let people control how the river is affected. What else would I need for that to work?

 

[ScaryMJDiamcreep]

Hmm, seems like there'd need to be some kind of underground rivers feeding into the geyser's resivoir(sorry if I misspelled that).

Also, it's likely that there wouldn't be any sharp turns unless these daily speed-ups are a relatively recent thing, cause they'd just cause the river to carve through stuff it would normally have gone around. Even then, depending on how recent they started, most of the sharp bends would have become islands by now. I'm not the best at geography, so I don't know how long that would take.

 

[Svrtnsse]

You might add walls along the river. It's not unthinkable that when the water speeds up like that, the water level rises. You probably don't need to have walls, but it could be interesting?

 

[Devor]

I haven't done much of anything about the map, but I agree it'll need a pretty straight path, and walls at least in sections of it. It would probably need manmade reinforcements and changes throughout the length of the river.

 

[ThinkerX]

Tidal slough. My part of the world, we have tides in excess of 25 feet (7 meters). The world famous (for fishing) Kenai river is nearby; when the tide comes in, the last few miles of the river actually reverse course. Given the correct alignment, I suppose a tidal slough could act the other way - speed craft up for the last six or eight miles of the trip.

 

[skip.knox]

Water does a lot of damage, and the faster it goes, the more damage it does. Erosion of the banks. Sweep debris downstream. Woe to any watermills along the way. Or river craft, for that matter. It would tear up docks. Probably would disrupt fish and plant life. Maybe your magical craft could just speed along on top of handwavium?

On the Rhine River, river traffic was firmly in the hands of cities and guilds. Your goods were carried along in one bottom, land at a city, get weighed and inspected, pay some taxes, all handling done by local longshoremen, then put into a *dfferent* boat. You go ten or fifteen miles and do it again. There were scores of stops before you reached the North Sea.

I could see something akin to that. It's the locals who have the ability (and permission) to speed boats. They fly just above the water, or magically plow through the water at high speeds, or some other device. Having the water itself move that fast? I dunno.

 

[Night Gardener]

It should be a man-engineered spur, perhaps a canal next to the river, that can be sped up from a resevoir. The resevoir can be filled from diverted river waters, filled to capacity, and released into an engineered spillway canal lane a few times a day, or however long it takes to fill the resevoir.

Like aqueducts, the canal would need a slope over the run to keep the momentum of the water flowing. Locks and levvees would probably be necessary to complete very long distances, also powered by resevoirs. This could be effectively coordinated for almost no interuption in speed with signals, like oncoming trains.

Don't forget Archimedes screw, that uses the downward flow of water under gravity to actually lift the water to higher elevations to fill resevoirs.

You would NOT want to release spillway gates with boats lined up like a start line with a starters pistol. They would need to cue into the currents single file like people using intertubes to slalom into a high speed jet at a waterpark attraction. If this is an engineered canal, using underground pipes to act as waterjets would help increase efficiency, and with a massive feat of engineering could be a gravity fed relay of resevoirs, ready to boats with consistent speeds and ease currents into any navigable turns.

So, you'd have a natural rapidly flowing river, with an artificial one running parallel to it. Along the length of the canal, would be diverted artificial ponds (resevoirs) that coordinate with levees or jets, to increase and maintain speed. All with a little bit of help from engineering and good ol' gravity.

Merchants get off the real river, pay a fee, wait in a water-line cue and much like an attendent at a water park, get pushed into the currents with enough space in between to avoid collision. Hopefully..

 

[Devor]

skip.knox, Night Gardener, that sounds like modest man-made reinforcements won't be enough, and that it needs to be closer to a completely man-made water shoot. I was hoping to avoid that, but I really like what Night Gardener suggested, having it be kind of two rivers, one the natural bend and one a fast-running man made expressway that's well-connected to it, like you see sometimes with highway systems. That helps to smooth out some other questions, like what does this mean for the fish and fauna (well, there's nothing in the shoot, unless they put something there to keep it clean) and what this means for sewage water (they can dump the sewage in the normal river.... ahh, the sweet, sweet river water).

So that leaves one last question.... water from a geyser, sure the river needs a slope.... but is that enough to keep the water moving forward instead of flooding? Are there some ways of pushing the water forward?

 

[Night Gardener]

Gravity (slope rise/run) and curvatures/ embankment geometry would need some planning. Changes to the bottom topography can help stabilize or increase a current. Adding water (jets and siphons) at key points will keep the water from simply 'rising' (flooding) and keep up the momentum for miles. That's why when dams break in uncontrolled ways, the devestation is catastrophic. The same dam made to release water into controlled, engineered spillways is pretty safe and predictable, and the momentum of the water can be harnessed in all kinds of useful ways.

Water will eventually seek level. In your canal, should fast waters be released into stiller waters (not static water. Unless you dam and levee the end of the canal, the water won't be able to fill up like a bath tub) then the current will change, and get faster. Water has to move until it's blocked and is allowed to seek level. You can conduct a simple experiment with a paper plate in your kitchen sink and a glass of water. Fold the plate into a "u" shape, and hold it under a bit of running water from the tap, slightly angled to the bottom (I used a knife to prop under one end of the plate under the faucet to create a gentle slope). Now, pour a glass of water into the channel. The water will rise a bit, but monentum will increase for as long as there's water to pour from the cup. Longer channel? Add more cups.

The man-made canal would likely have water in it at all times, not be engineered to run dry between scheduled uses, like the LA canals that were recently re-routed. (If you saw the Terminator 2 movie, they were riding a motorcycle in the canals escaping the AI.)

Flora and fauna may be quite happy in a high current a few times a day. It wouldn't be much different than a tidal area in that respect. They would probably not want to be run over by watercraft zooming through at high speeds. I would recommend a solid or gated levee mechanism to keep larger creatures out of traffic.

If you don't want to render imagery of poured concrete bulkheads and engineered walls, lining the river banks with chatter (large, medium, small, gravel interlocking stones in a specific size sequence to reinforce the riverbanks and direct the flow of water) might work. A dry stacked or mortared stone wall reinforcing the banks and key areas of the bottom, if not the entirety, would suffice. Even timber pilings would hold up for years at a time.

And, a wee bit of hydrodynamics: water will always seek level. If you don't give it a level spot, it will keep flowing. That's why rivers are rivers and lakes are lakes. Rivers are literally *going* somewhere, there's an unlevelness to the run and gravity demands that it keep moving.

Lakes can be headwaters to rivers, or part of river chains, because they are level to a certain point... filling up like a bath tub.. and somewhere water will likely overflow a bank... and the water is to be influenced by gravity again... and keep moving until it can fill up the next 'level' spot.

Would a canal wash away under the sudden release of water from a spillway? If built correctly, no.

I live in a region where dams are frequently drained in the rainy season. Year to year, I haven't noticed huge drastic changes to the lower elevations that have been left in a 'natural' river condition. The water might get turbid, but I can't say I've seen anything dramatic, like impactful changes to the cliff faces or ruined river banks, uprooted trees, etc.

If it were a daily occurance, it might look very different from occassional spillway release.

But, I think the diverted resevoirs and canal next to the river would be easier to engineer and operate than trying to manipulate and move waters from further away.

Slope calculations in hydrodynamics are pretty complicated, but ancient people were able to engineer some amazingly complex devices using little mechanical action and mostly gravity. If your people master mechanical devices powered by water, it can get very interesting indeed.

I bet you could run two canals next to the river... one to flow with the existing river current, and the other against the real river current. Use the same diverted waters twice.

If you have a few minutes to kill, go to YouTube and look up hydrodynamics laboratories or experiments conducted by watershed committees. They study this exact thing you're talking about (dams impacting downstream) using TONS of water and scale models to study engineering solutions. I think NASA or the US Navy Laboratory posts videos on this kind of stuff, too.

 

[Laurence]

Potential for some cool bridges I imagine! Ie. when the river wasn't flowing fast and high, the bridge would appear to be really tall. When it's flowing the water almost laps over your feet as your cross.