#1: the idea of a bench is good, but compositionally it's not quite there. Firstly, it's too close to left and bottom edges. Secondly, the top overlaps with the bridge... I think you need to shoot from an perspective, and with a focal length, such that there's a bit of water visually separating the two (i.e. shoot from higher up/closer in), and/or be looking more along the bench (requires a very wide angle to still get the bridge in) rather than through it. Finally, it's a bit big and heavy in the frame. You could also consider the Rule of Thirds, and frame or crop such that either the horizon or the main line through the bridge is a third from the top of the image.
#2: Again, the horizon is a bit low in the frame... try to divide the picture into thirds. Some more foreground would have been good.
#3: Good shot. It feels pretty "tight" around the edges, with the parts framing the water only just included in frame... angling the camera more horizontally - possibly with a step back and/or slightly wider angle - would be a more conventional choice, though not necessarily better. I'm not a big fan of the brown colour - maybe a grayscale conversion?
#4: Another where Rule of Thirds might help prevent the top seeming overly heavy/dominant. Unfortunately, from that angle the tree trunk isn't clearly differentiated from the falls by more white water, so it's a bit of an effort to visually separate from its background. I feel there's no sense of completion at the left, right or top, and the eye is carried right to the sides and top and wants to travel out. It's often a good idea to find some elements that encourage the eye to circle throughout the photo without getting too close to the edges....
Cheers,
Tony