On 14/05/2010 18:21, Bruce wrote:

How many off-shore wind turbines do you get for £14M

On current estimates, the likely cost of a Severn Barrage is between
£23 billion and £30 billion.

Where are you getting your figures from?

You haven't said where your figures come from.

snip

and often would
they need replacing over the next 200 years?

A tidal barrage in the Severn would silt up after three or four
decades. What would you do then?

On what do you base that opinion?

One of my research contractors, who is also a personal friend, is a
sedimentologist has worked on every single Severn Barrage study since
the 1970s. There have been quite a few studies.

Lasting 200 years is one of the supposed advantages of the Barrage. Are
you saying that the supporters of the scheme are just ignoring
inconvenient facts?

All hydro-electric dams suffer from siltation. For example, the Aswan
High Dam in Egypt is now almost useless for power generation because
the silting has significantly reduced its capacity. To varying
degrees, the same is true of the dams on the Colorado River in the
USA. These are among the largest hydro-electric dams in the world.

But they are all sites on rivers that have a fairly low silt content.
In contrast, the Severn Barrage will be located on an estuary with an
extremely high silt content. Siltation is unavoidable. Even a design
that minimises the problem will last only a few decades.

I know I shouldn't argue with experts but why won't most of the silt
just wash through? The fine stuff will stay in suspension for a long
time and the coarser silt would be dropped upstream of the site of the
barrage regardless of whether there is a barrage or not and already be
dredged out of the deep water channel as a matter of course.