Graeme Wall wrote:
On 17/11/2019 09:04, wrote:
On Sat, 16 Nov 2019 14:48:05 +0000
Recliner wrote:
https://www.flickr.com/photos/reclin...-friend/lightb
ox/

I wonder why the water tunnels are so deep. You'd think when pumping water
around you'd want them to be as shallow as possible since water is heavy stuff
and requires huge amounts of energy to pump back uphill.


The problem with that diagram is that it shows depth below ground level,
not sea level (or river level in this case), so it gives a distorted
view of the actual depths.

One possible reason for a deep water tunnel is to give it a straight run
so you don't have to keep pumping water uphill at intermediate points on
the route.


The tideway tunnel needs to be below both existing sewage/storm water
tunnels and the under-river rail tunnels, such as the deep Jubilee tunnels
near Waterloo. With current tunneling techniques, they don't need to stay
in the clay layer, and nor do they have to build watertight underground
stations, so they might as well go deep.