How does Stuart Elding know that a barrier at the river outfall would cost four times as much ?
Certainly a barrier at the outfall would be more expensive but the cost of raising and maintaining the banks from the present proposed site to the outfall to provide similar protection would offset this. A barrier at the outfall would protect a much larger area and provide much more benefit and still be economically viable .
As for affecting shipping, the only time this would happen would be when the barrier was closed for a few hours ahead of a predicted surge.
The rest of the time it would remain open and not interfere with shipping, gravity flow, pumping or environmental issues.
Also placed there it would not cause siltation in the river which could be a major issue at the London Road site.