Why the Amazon River Can't Be Crossed by Bridge (2018) | Hacker News Reader

Why the Amazon River Can't Be Crossed by Bridge (2018)

cntraveler.com

121 pointsapsec11250 comments

When I was young (I think I was 18 years old), me and my dad traveled across all the length of Amazon river (from Belém to Manaus) in a crowded boat sleeping on hammocks, it was a 6 days trip. https://goo.gl/maps/BFkCPx1HR1n

In some places the river was really narrow and almost could be crossed by swimming, but there where times that I couldn't see any of the two margins because of its enormous width.

Is was a really great experience, got to talk to indigenous people, saw a lot of botos cor-de-rosa (https://en.wikipedia.org/wiki/Amazon_river_dolphin) and got to eat amazing local dishes.

How did you set this up? Doesn't seem like the kind of tourist package you'd see on TripAdvisor.

The river is / was the main highway, not sure about now with more year round roads etc, but when I was last in the area, long time ago now mind,you would just turn up and get on the boat. It wasn't comfortable, wasn't all that enjoyable after (x) hours and (y) days.

Lots of being bored, interspersed with the odd enjoyable / memorable moments. Which looking back on, is all you remember :)

Isn't Belém to Manaus the trip Jules Verne described in 800 miles on the Amazon? I wanted to take that trip since I was 10.

Always happy when bridges get discussed here. Having built (a couple of) bridges across the Mississippi, i can attest that it is possible to build a bridge across the Amazon. This headline is appears to be click bait

A river rising 30 feet is no big deal. I think the Amazon rises more than that actually. The Mississippi very often rises to 40 feet.More in some years. Here's a video of a 300yr flood hitting in the middle of bridge construction - https://www.youtube.com/watch?v=Orj6B46PJbY (skip and pause at 0:17)

The real issue is that the area is sparsely populated so you'd end up with a lot of bridges to nowhere.

To natural resources ready to be looted. Much easier moving big machines to chop huge trees quickly if you have a road.

>the river rises thirty feet, and crossings that were once three miles wide can balloon to thirty miles in a matter of weeks.

My impression wasn't so much that it was the 30 feet rise, but the fact that it added 27 miles to the width of the river. Does the Mississippi do that as well? (The Ohio/Monongahela/Allegheny are my baseline, so it's harder to comprehend rivers that do stuff like this!)

This is also hardly an issue, as there are bridges longer than that [0].

As others have pointed out, the main issue is given at the end of the article: nobody needs such a bridge.

> But the real reason for the lack of bridges is simply this: the Amazon Basin has very few roads for bridges to connect. The dense rainforest is sparsely populated outside of a few large cities, and the river itself is the main highway for those traveling through the region.

[0] https://en.wikipedia.org/wiki/List_of_longest_bridges

The Mississippi would, but doesn't to that scale today, because the Army Core has leveed/dyked in most places.

You can see in the pictures here http://bit.ly/2u7f2ta that there is a lot of "marsh" beyond where the river bank ends. You just have to extend the roadway as far as you like. You can see how the bridge extends beyond the river on both sides.

This particular bridge for example has 18 miles of approach roadways. Only about 1600 feet of that, spans the Mississippi.

In short, if flooding adds 27 miles or 270 miles of width, the engineering is pretty much the same. You just have to know, where to start and finish :-)

Very interesting! Thanks for this.

The place where I was surprised to learn there's no bridge is between Kinshasa and Brazzaville, capital cities of their respective countries, with populations of about 11 million and 2 million people.

I've then heard that the lack of a bridge may be more due to politics than to engineering problems, but how hard do you think it would be to bridge the Congo in that area?

>For most of its length, the Amazon isn't anywhere close to too wide to bridge—in the dry season. But during the rainy season, the river rises thirty feet, and crossings that were once three miles wide can balloon to thirty miles in a matter of weeks. The soft sediment that makes up the river bank is constantly eroding, and the river is often full of debris, including floating vegetation islands called matupás, which can measure up to 10 square acres. It's a civil engineer's worst nightmare.

Isn't this the predominance of what the ACE (Army Corps of Engineers) deals with when it comes to the Mississippi River[0]?

[0] - https://www.tulane.edu/~bfleury/envirobio/enviroweb/FloodCon...

up to 10 square acres

I cannot fathom this 4 dimensional unit!

I think square acres might work as the article could be referring to the area moment of inertia of the floating vegetation (https://en.wikipedia.org/wiki/Second_moment_of_area). I suspect this is not the intended meaning though. :)

4D: Volume and time! Obvious!

The demonstration is trivial and is left as an exercise for the reader.

Of course, but what is the conversation factor between seconds and feet?

983571056i ft = 1s

That's because a fathom is a unit of length (or depth) so 4 in to 1 obviously isn't going to work.

What does work have to do with any of this? Sure, the water acts on the floating vegetation in the direction of displacement, but without a measure of the weight of the islands, it's somewhat meaningless.

Clearly they mean 10^2 acres = 100 acres.

BIMDAS!