Disastrous to who (or what)?
It would certainly create changes to the estuary, and may adversely affect some plants and animals!
On the other hand it would generate "free" electricity that was carbon neutral (after building costs). If this proved successful other similar barrages may be built causing a loss in share value of the Nuclear and fossil fueled generators of electricity. This could have a knock on effect with the big American petrochemical industries creating panic and wholescale redundancies! Is the price of Green "Free" Electricity worth it?
Now let's see ........ insert your choice of three lettered answer here (      )



As to the previous posts concerning gravitational effects ............ Why do you think the moon always faces the same way?
I suspect the Apollo Moon landings have had a greater effect (every action .... )