I would like to define slope classes (e.g. gentle or steep) from the separation distances of contour lines e.g if the separation distance is greater than 100 m, than the slope will be gentle. If the separation distance is smaller than 100 m, than the slope will be steep.
Thank you for your suggestions, but these usual ways don't work here on tidal flats (see attached) with low slopes. The contour lines make differences vizualising the river direction, but the method surface-slope not really. With this method I can't consider the direction. Also reclassification doesn't bring a benefit.