I find the square openings quite puzzling too, but even more so he rectangular, vertical ones!!
edit: in the name of clarity, and as an apology for the poor quality of the picture,
There are types of elements which show
- a vertical steel girder, which looks like it may have a positionned the way it is to help support the crumbling wall
- square opening with steel doors. There are three or four of these barely visible as hidden by the vegetaion, about 2ft above the waterline and a 2 others either side of the steel girder
- two rectangular openings on the left side of the girder. they are less visible as their openings have been infilled with bricks, however the door of one is still in place - albeit not visible as at the wrong angle on this picture! The hinges to the other one are still visible on the picture so it definitely used to have a closing door in place?
-the 4th thing is possibly the most difficult to see and protrudes at a right angle about a foot from the top of the wall. It goes out for about one foot and hen has a right angle, you can just about make theoutline of its vertical element in the foliage, against the white sky.
to me this looks like it may have been a moving, mechanical element, like a governor? edit again just some sort of lever...