It's too much work for me to do it for you but what I would do is to assume that the orange cable and the blue scale are always there. Then I'd do there steps
- Convert RGB into hsv color space,
- Threshold the S channel to get high S areas (the cable and blue scale) then set those pixels to zero in the v channel.
- Take the histogram of the V channel, but ignore the blackened pixels at bin 0. Find the big hump - presumably it's the large sand area on the bottom.
- Threshold the v channel to get just the sand.
- Use activecontour (demo attached) to get the "envelope" of the sand, which will jump across the gaps where the blackened cable and scale are as well as give you a smooth upper border.
Code that up and let us know how it goes.
