My immediate reaction is that the 'greens' are certainly not keen on the idea of the barrage - if anything, it's just something the government can be seen to be doing that seems green. Using such a sensitive area as an estuary hasn't been done in many places, and where it has been, there hasn't been proper tabs kept on the effects on wildlife - but it's pretty likely, considering you are utterly changing the tides timing and height, the mixing of the two waters - the whole habitat essentially, it is going to be utterly bad news. And this is the 2nd highest tidal change in the world! For me, the archaeology is way down the list in importance, I'm afraid. But if it gives the anti barrage arguments more leverage, then great... also there are other clean ways of making energy and we could always look at energy efficiency. phew