For something that “small” you can likely get away without using a drone.
The number of photos required depends on the location though.
My best guess would be somewhere between 500 and 1000 photos if you want to capture every little detail.
Less if you don’t need sub-millimeter accuracy.
Either way, the water is going to cause you issues. So you’d likely have to work with control points.
If you can return to the capture area you can shoot more photos as needed if what you got the first time around isn’t enough.
Mind, though, that I am basing this on the camera I use, which only takes 12MP photos at best.
If yours does better you can get away with taking fewer photos.
But maybe someone else has more/better suggestions 