The Ramp tool enables you to select two locations on your Landscape and create a flat ramp between the two points, with a falloff you specify for the sides.
In the Landscape tool, in the Sculpt mode, select the Ramp tool.
In the viewport on your Landscape, Left-click and drag or simply Left-click in two different places to mark the beginning and end points of the ramp.
If you change your mind about adding a ramp after starting to set the beginning and end points, you can click Reset to clear them.
Select either marker and adjust its position. In this case, it has been moved along the Z-axis above the Landscape surface.
When you're satisfied with the position, click the Add Ramp button in the Tool Settings to create the ramp.
Now, you'll have a ramp that has been sculpted into your heightmap.
Sets the width of the ramp.
Sets the edge falloff on the sides of the ramp where it merges inot the rest of the landscape. This falloff gives a softness to the edge flow on these sides. A setting of 0 means no falloff; a setting of 1 means all falloff and no flat surface for the ramp.