The empoundment can be made more cheaply and without the use of
concrete by using a Gabion Wall type construction, with dredged
material, or maybe loose rock, with an impermeable membrane
incorporated. This will reduce the carbon cost during construction.

If the wall is ever demolished the only concrete to dispose of will be
the turbine housing.

If wind turbines are constructed on the wall, they will need to be
piled, but this will still be cheaper than fabricating the wall of
concrete.