I'm sure there is lots of information out there as regards the enviromental impact of a barrier (look at Holland 30km Dyke creating a freshwater inland lake as we speak). In Brittany there is a barrier across the mouth of an estuary that produces the cheapest electricity (unit cost) in the world.

I think a lot of computer modeling went into the artificial islands off the coast of Bahrain, so hopefully we have the technology, knowledge and computing power to build this barrier with few 'unintended consequences'.
Yes I've heard of chaos theory but if all else fails the barrier is reversable.

I think the benefits of the preservation of the inhabited land round the Wash would make it cost effective, give us a 1,000 years breathing space by which time, with the loss of fossil fuels and we can remove it.
David Rossi
Address supplied