Hacker News Reader

Comment by twic | Hacker News Reader

At least Boris is fixated on absurd bridges that will never be built, not walls.

A brief response from a structural engineer:

https://theconversation.com/boris-johnsons-english-channel-b...

Artificial islands, he likes those too. And why not, the UK used to do megascale engineering at the drop of a hat. Now we can't even do railways.

A response from the Telegraph. http://www.telegraph.co.uk/travel/lists/worlds-longest-bridg...

For comparison they show the following list.

  Where                                | Length in kilometres
  Danyang–Kunshan Grand Bridge, China    165
  Changhua-Kaohsiung Viaduct, Taiwan     157
  Tianjin Grand Bridge, China            114
  Hong Kong-Zhuhai-Macau Bridge, China   55
  Bang Na Expressway, Thailand           54
  Lake Pontchartrain Causeway, USA       38
  > 'Boris Bridge', UK-France            35

In light of all these other megastructures the proposed Boris Bridge doesn't sound too unreasonable? Considering the two economies it would link… Linking Ireland and the UK, that'd be another matter entirely.

The Danyang-Kunshan is mainly over land. It's an elevated railway line. It does cross the Yangcheng Lake, but that part is only 9km long. It's not a suspended bridge, there are piles every 80m. Not suitable for heavy maritime traffic. The lake has an average depth of 2m. https://www.lakepedia.com/lake/yangcheng.html It's not comparable as a channel crossing.

https://en.wikipedia.org/wiki/Danyang%E2%80%93Kunshan_Grand_...

Likewise the depth of Jiaozhou bay is 10 to 15m. The channel is 45m deep between Calais and Dover (the shortest and shallowest crossing). Moreover the strait of Dover (or Pas de Calais in french) is the busiest shipping lane in the world

http://i.dailymail.co.uk/i/pix/2014/05/22/article-2636152-1E...

The only bridge on that list even remotely comparable is the Hong Kong-Zhuhai-Macau Bridge. The rest are essentially elevated highways which are almost entirely over land.

I am not a civil engineer so this is just some uninformed speculation:

- The channel goes to about 45m deep between Dover and Calais, while the path of the HK bridge only goes to about 20m depth.

- The bay formed by the Pearl River is more enclosed and protected from weather than any part of the channel.

- The bridge would need sections elevated high enough for future mega container ships.

- The HK bridge cost $15.9b. I'd expect the channel bridge to cost much more. It might be cheaper to just build another tunnel.

Edit: and, of course, by the time I finish this comment there are 10 more saying basically the same thing.

The Hong Kong-Zhuhai-Macau includes a section of tunnel, so it doesn't need the height above the water that a pure bridge crossing would require.

The size of ships and number of ships going through the English channel are much larger than any of the bridges listed above apart from possibly the HK <-> Macau bridge.

Some of those can't admit any ships, never mind the biggest ships on the ocean.

For example, the Lake Pontchartrain Causeway impacts quite small boats:

https://en.wikipedia.org/wiki/Lake_Pontchartrain_Causeway#/m...

That's a completely different project than something that won't impact traffic that needs 50 or 70 meters of clearance.

The engineer's statements linked by the parent poster mentions Danyang-Kunshan:

"the longest bridge in the world is the Danyang–Kunshan Grand Bridge in China. It is mostly a conventional bridge made from columns sunk into the seabed, although it has a cable-stayed section. The bridge is 165km long (just over 100 miles) but the short distance between the columns would not do for the busy Channel."

the problem they say is that this would be on one of the world's most active shipping lane and that boats would need to be able to pass under the bridge, requiring it to be much higher than the other bridges of that list

Can someone explain to me why a wall can't be built?

I know people say it shouldn't be built - but I don't understand why people say we "can't" build it when they've been built before, and we've done endlessly more complex things - rockets, going to the moon, et (all while China is building artificial islands and the like).

In comparison to some of those feats, a wall seems trivial.

Cross-post: http://johnsalvatier.org/blog/2017/reality-has-a-surprising-...

Let’s consider some of these details. Something I think people don’t consider is that there are a non-trivial number of land animal species that migrate across the border. They have no concept of nation-states, and for some, our xenophobic electorate is basically passing a death sentence. The wall would devastate several important ecosystems, especially in the Rio Grande Valley.

Walls also need to be maintained, like any other piece of infrastructure. Have you ever visited the great state of Michigan? We can’t even handle roads. How will the federal government, which doesn’t have the best track record with maintaining infrastructure, deal with a 2,000+ mile-long wall?

Another issue is surveillance. Who will watch the entire thing? Who will make sure someone isn’t chipping away at the other side with a spoon or trying to dig under it? You can’t watch thousands of miles of wall very easily.

There are all kinds of issues with this (oh, funding is a big one too), and this just scratches the surface. If you Google “Trump border wall problems”, plenty of articles have already been written that go into much more detail.

>xenophobic

Yeah there's no way any friendly, rational person can look at Mexico and possibly come to the conclusion of "no thanks, I'd prefer not to have that here".

Mexico has no problem with extreme prejudice towards the rest of Latin America. Policies that people would decry x1000 if the US did them to poor Mexicans. But somehow the US applying some basic restriction to Mexico is "xenophobic" among other horrible phobias.

There are wall prototypes that allow for small/medium size animal passage, but not humans. Also, the entire southern border won be walled. If there is a natural border, mountainous terrain, etc, the wall won't be built there. While the area may be unsuitable for human crossing animals may not have a problem with it.

Roads have different material and structural requirements than walls. Maintenance will obviously cost money, but it serves a purpose. 450,000 people were caught in 2016 trying to illegally cross the southern border. Now imagine how many made it through. I assume you will not find this argument very convincing if you are the kind of person that believes that illegal immigrants make money for the state they illegally live in.

CBP border agents monitor the wall. And again, it isn't just 2000 miles of wall. It is "smart wall", where it will have the most impact to prevent crossings

So wait, we're going to have people just stare south for 8 hours a day? How is this not 'government waste'?

Well, hundreds of thousands of people try to cross the southern us border every year. It is only wasteful if they aren't accomplishing anything. And, these days we have video cameras, so one person can monitor multiple miles of the wall from an operations center

Then why do we need a wall if we're just going to use cameras anyway? It'll slow them down, yeah, but just by the amount of time that it takes to climb a ladder, cut some wire, whatever. Maybe 2 minutes max?

The cameras aren't going to be directly on the wall, and they won't be easily accessible.

I'm confused. Are there going to be cameras? If they aren't on the wall, where are they? Hidden in some cactus or in a drone? Still, why a giant wall then if all it ends up being is a concrete hurdle?

Yes, but the camera won't be easily accessible at all, let alone from the Mexican side.

The wall is so people can't just mosey across the border. Even if you had cameras there, sending out a team once you see someone crossing would be very difficult to find them. With the wall, it will be passable but will take work and a fair amount of material like ladders, ropes, etc which will all take time, and allow for security to arrive with a greater chance of catching people.

But that's like a 3 minute delay, max.

How do you know how much time it takes to get from the closest dispatch center to the furthest possible point before the next dispatch center?

Ok, so napkin math time:

Assume you need 3 people to drive out to apprehend illegal crossings for officer safety. You also then need 3 others to watch while others are out apprehending and then be able to respond for other illegal crossings.

Assume 3 minutes to cross over the barriers per person.

Assume it takes you no time to see the crossing happen, you can tell the second a ladder is put up.

Assume the roads are dirt, but in good and dry conditions. So you can travel about 40 mph on them on average, including the time to accelerate from 0mph at the remote watch tower station and then back down to 0 to apprehend people. 40mph is 2/3 miles per minute, btw.

So, the minimum distance at 3 minutes to cross would then be 2 miles. Meaning you'd need about 6 guys every 2 miles. So about 12,000 people for the 2,000 mile border.

Now you can play with the numbers, and talk about capturing people that scatter into the interior, but you're still at about 1 officer per 1 mile (ish), not 1 officer per 10 miles or 100 miles of border, with significant downtime per officer per day.

You can't build a wall on the border because 2/3 of the border is over the middle (more accurately, the thalweg[0]) of the Rio Grande and the Colorado River. So you'd have to build it on the American side, most of which is private property that would have to be taken by eminent domain, and its owners compensated, many of whom would sue to prevent that – notably, Cards Against Humanity[1].

[0] https://en.wikipedia.org/wiki/Thalweg [1] https://cardsagainsthumanitystopsthewall.com

Parent never claimed the wall can't be built. Depending on your interpretation, they claimed it will never be built, or merely claimed that Boris isn't obsessed with a wall.

To be fair to joelrunyon, he wasn't saying that i was claiming that - he was using my feeble witticism as a jumping-off point to ask a question about «why people say we "can't" build it» (emphasis mine).

FWIW, i did indeed mean to imply that Trump's wall is absurd and will never be built. I assume that, like the Channel bridge, the Hyperloop, the Freedom Ship, etc, it could be built, given enough time and money. I just don't think that there are enough people who think it's worth the cost to pay for it.

Thank you for the presumption of good will. Doesn't happen much online these days. Cheers.

Not the answer you’re looking for, but if you think about short-term and long-term political willpower, “shouldn’t” and “can’t” turn out to be the same thing.

I heard that a big portion of the border is over a mountain range, both making actual wall construction hard and almost fulfils the same role of a wall?

Saying 'walls can't be built' is just an ideological exaggeration.

Why do you think the wall isn't happening? They are building prototypes right now.

Is the wall absurd because people will find another way around? Or because you think it literally can't be built? Or it's absurd to protect the borders of a country? Or is it absurd simply because it is proposed by Trump and you just don't like him?

Also, I don't see why this bridge can't be similar to the Chesapeake Bay bridge. That has a 1km span for ships up to 60m to pass under.

I think borders between countries that keep people out are inhumane. Also building literal walls at great cost is to me the opposite of what we need - we need to connect people not separate them. I do not believe immigrants from South America and Central America are a threat to us.

Why just countries? Do you live your personal life like this? Is your private property, and private house with locks on it inhumane?

The United States isn’t your backyard.

Well, it's more my back yard than a non-citizen without a valid visa who illegally crossed the border.

The wall isn’t happening because it’s nothing more than a campaign lie and an extension of the electorate’s racism, which, like the wall, has no place in modern society and is unsustainable in the long-term.

So was the Iron Curtain. Arguments like that don't necessarily keep governments from embarking on foolish projects.

Sustainability in this case also is a question of scale and the particular design and purpose. Both Hadrian's Wall and the Limes lasted for quite some time.

Misguided and malevolent as the intent behind that wall may be if completed it quite likely will contribute to keeping people out of the US just as much as the Iron Curtain for some time was a mostly effective tool for keeping people inside certain countries.

So, is that wall desirable? No. Is it sustainable? That depends entirely on what resources the American people are willing to commit on its long-term upkeep.

Either way, building and maintaining such a wall is a colossal folly because the funds required to do so will of course be lacking for other, probably more beneficial projects.

Unfortunately, that doesn't necessarily mean it isn't happening.

So the wall isn't happening because it is a lie? That isn't a very strong argument.

The wall isn’t happening because, among other reasons, 2,000-mile long structures aren’t trivial to build, especially when subject to the whims of the political machine. Have you considered too just how long the thing would take? We’d probably be well into the next administration by the time it even got close.

No one ever argued for a 2000 mile long structure that completely disregards any natural wall that already exists

Immigration is a tough issue, and so are xenophobia and racism. But spending tens or hundreds of billions of dollars to build a wall that has countless logistical problems (say goodbye to several migratory species that cross the border; hope none of them are important for the food chain), is just so mind-bogglingly shortsighted and cruel. How many immigrants could we help for that much money?

Have Americans so quickly forgotten that, up until rather recently, there was no immigration policy? You could just come to the US to flee whatever terrible life you had before, and nobody asked any questions. I feel incredibly fortunate that my mom’s side came here from Germany well before WWII. I wouldn’t want to prevent anyone else from having a chance to be here.

Why help immigrants that illegally crossed the border? Why not help immigrants who come here legally, and US citizens? To do that you can't keep having the population of medium sized city sneaking into the country every year.

And Yes, there was immigration policy, going back hundreds of years. Remember the Chinese exclusion acts? Also, America highly favored not just white Europeans, but a specific type of white North/Western European from the beginning

Yes.

Reply on news.ycombinator.com