The system (1) has a set of segments (2) assembled together to form a gutter that is open towards a top and form a fence, where each segment comprises walls that rise laterally from a base plate (11). An inlet opening is provided in the segments and a side wall that faces away from an area to be protected. A flap closes off the inlet opening, and the segments are formed of plastic plates that are inserted into each other. Accommodation openings are provided in the side wall and receive insertion elements complementary to the accommodation openings.
