Steve,
your picture shows a great bay. I've never seen that before.
Kaplan turbine, an interesting technology for fixed hydro electric applications but probably not for coastal tidal energy sources.
My turbine knowledge doesn't go very deep. I have always worked on the side of the electrical generator.
This double inlet has massive volumes of water and a fixed hydro style application would not work there. Something that floated so it rose and fell with the tide would make more sense.
I would always ask a turbine specialist about such specific questions as you ask. My former section manager was a specialist in water and steam turbines - two very different worlds. If he
is still alive, he should be around 90 years old. I'm going to ask around. However, it will take a while - we have a pandemic here.

I'll get back to you via PM when I know more.