The Radiate Runoff Surface feature creates a runoff surface based on a specific edge and the direction of points that you select on the edge.
Only one edge can be selected.
After you select the edge, the start point and the end point are given as the default directions. Enter different values between the X axis and Y axis to adjust the directions.
The surface you create sometimes does not suit your requirements. For example, if the continuity of the surface is poor, add extra points to the edge to improve the quality.