I took a narrowboat over the Pontcysyllte Aqueduct [0] a couple summers ago. It's really strange to be on a boat 130 feet up in the air, especially with no guard rail on the side.
Pontcysyllte is magical, not least thanks to its setting in delightful countryside.
Barton Swing Aqueduct is in an unattractive patch of urban Manchester, but impressive in engineering terms. It’s a canal-over-canal bridge which can swing aside to let big ships through:
If I'm thinking it right, the weight carried by that bridge is much greater than for something like a typical road bridge. On the other hand, the weight also doesn't increase at all when a ship passes over it.
Under-appreciated fact, this weight difference was one of the major reasons for switching from canals to railways, in their early days.
The engineering needed to hold up a train (along a hillside, never mind over a bridge) is much cheaper than that needed to hold up a canal, because a train is much lighter than all that water.
1. When a boat enters a section of canal (i.e. between lock gates), the water level rises equally along that section, and consequently the weight of the boat is spread over the bed of that section.
2. ...Except that, if the level is maintained by water flowing over a weir, the weight of the boat is compensated for by a decrease in the water content of the canal.
3. Water level changes from launching a boat, or the lock operations to bring it into a section, propagate as waves, so do not take effect throughout the section immediately.
4. A moving boat creates waves in a canal. When the boat occupies a significant part of the canal's cross-section, water flowing around the boat's hull from stem to stern lowers the water level alongside the boat. I guess that it is possible for boats crossing an aqueduct to reduce the load on that aqueduct (while the bow wave may increase it.)
And no matter how heavy are the ships that are crossing the bridge, the weight of the bridge always stays the same as when no ships are crossing it (provided that water level stays the same). See also: https://en.wikipedia.org/wiki/Falkirk_Wheel
I'm sorry but as an engineer there is no way aqeduct is from 1670, it looks mid 1800s (and definitely no earlier than 1800).
Edit: Google shows canal du midi is indeed from 1670 but this aqeduct section is later, completed in 1858 (the order was decreed by Napoleon himself according to wiki)
Ah yes, they are both very nice structures that would have taken some good engineering at the time. I wonder what would have been used as the impermeable water barrier - puddle clay or similar?
Impressive, I had no idea that it is that old. Not quite fossa carolina old ( https://en.wikipedia.org/wiki/Fossa_Carolina ) but compared to the canal du midi with all its impressive locks that one was just a series of ponds connected by slides.
Well, Roman antiquity is full of infrastructure far beyond and above anything from the middle ages, that's a given.
The surprising part about fossa carolinga is how it happened at a time when most known infrastructure projects were hardly more than permanently staffed camps for a roaming band of warlords.
Here's one in New Jersey [1], carrying the D&R Canal parallel to the Delaware, across a tributary creek. It's part of a park, you can bike or hike across here, and I was really quite astounded the first time I came across it.
This whole area is pretty much paradise to bicyclists, from the D&R Canal's 70 miles of towpath, to the 15 miles of the Colombia Trail. There's a huge amount of riding to be done, completely off roadways and safe from cars.
Or the Niederfinow boat lift, which is on the same canal system as the Magdeburg water bridge, just 200km to the east: https://en.wikipedia.org/wiki/Niederfinow_Boat_Lift. I am glad they decided not to tear down the old one (from 1934) but built the new one right beside it over the last years.
Work started in 1998, with construction taking six years and costing €501 million.
Given that large US construction projects always seem to come out costing multiple billions of dollars, this seems quite cheap. The Eastern span of the Bay Bridge ran about $8 billion and Boston's Big Dig also multiple billions.
We Germans have noticed this deficiency in our history of construction projects and are currently making up for it in one go with the new Berlin Airport: original planned opening in 2011, still not done and currently about 3.7 billion EUR over budget.
