Originally Posted by
ChrisO
A website
www.merseybasin.org.uk, has a PDF document on it stating that the river has a depth of up to 30m and a tidal range of 10m
Yep. It varies depending on where in the river. The Sloyne is a natural deep channel at Tranmere, hence the tanker berth - the liners would anchor there. The Sloyne is 60 foot and 90 foot at a high tide (32 foot tides).
div>
There is a shoal just off the Pier Head which means liners can't sail at low tide. The depth at the Pier Head is deep enough, about 35 to 40 foot deep at low tide and 30 foot deeper at high. Modern liners have less depth that older ships, They are wider and flat bottomed.
The Crosby Channel has under water training walls that direct current up the channel, which keep it deep and clear. The current goes straight to the Wirral side of the river and down the dredged channel to the Manchester ship canal, keeping this side clear.
When the canal was built there was concern that currents would be affected. They were. The strong current was diverted mainly over to the Wirral side and sanded up the south end docks which required more expensive dredging. Only so much water enters the river on the rising tide and deeper channels will take most of the current (water), as water takes the line of least resistance.
The Garston Chanel is a sort of naturally deeper channel - which requires dredging to be operable by ocean going ships.
The Manchester Ship canal's first design was training walls from Runcorn to the Garston Channel. They thought the city would object. If the city had not objected the Liverpool side of the river would have been deeper with naturally water cut channels.
A barrage from New Brighton to Bootle would make it all academic and all would be deep once dredged inside the barrier, as sand, or little sand, would not be washed into the river by the strong currents.
The same sand is washed in and out from Liverpool Bay. If most of this sand is removed (big task, but not impossible), instead of removing and dumping sand back into the bay, the river would remain very deep.
New York Harbour is only about 15 foot deep on average, with a coiuple of foot tide. Dredged channels were cut for big liners.
Near the ocean the bay's depth was deepened by explosives by the US Army Corps of Engineers to accommodate large container ships. If necessary that could happen at Liverpool.
Liverpool Docks have the advantage of "impounding" - deepening the docks by pumping water from the river at lower high tides. Expensive in fuel to do this. This saved the expense of deepening some docks. Ships would enter the river locks and raised up to the dock's "impounded" depths to accommodate their deep draughts. Fast pumps would fill the locks quickly to get a number of large vessels in on the high tide.
The sea level would have to rise by many, many feet to affect Liverpool. Many feet in sea level rise would be catastrophic world-wide. Liverpool is pretty safe. London would mainly disappear.
Bookmarks