Interesting choice to shoot this in a portrait aspect. I think you chose wisely. The foreground is interesting and the beams of light in the sky makes this shot more dramatic.
love the rocks and pebbles. The slight curve of the horizon mimics the shape of the rocks. I would be tempted to crop half the sky out. As it is it looks like three seperate images, the sand and rocks, the band of water and the sky. Something breaking the horizon ( a boat, a bird or rock etc) would have been perfect