Computer Vision Techniques to find Slope of beach in the 2D Images !!!?

What I am planning to do is to calculate the height and estimate the slope of the segmented Object. The camera will be static and the Object of Interest is the slope of the beach. I am finding harder to use depth camera, as the minimum distance between slope and camera is 150 meters. Please see the attached Picture for more information. If you require more information please let me know, 🙂 Thanks for your help !!!.

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