In a model for a coastal section by the sea, the $x _ { 1 } x _ { 2 }$-plane describes the horizontal water surface and the line $g$ describes the shoreline. The plane $E$ represents the sea floor in the considered section. A buoy floats on the water surface at the location corresponding to the coordinate origin $O$. One unit of length corresponds to one meter in reality.
Determine the angle at which the sea floor slopes down relative to the water surface.