The runoff from tiny groves in the soil during sheet erosion is called rill erosion.

Here's a breakdown:

* Sheet erosion: The uniform removal of a thin layer of soil by raindrops and overland flow.

* Rill erosion: As sheet erosion continues, the water flow concentrates into small channels called rills. These channels become deeper and wider over time.

So, the tiny groves in the soil are the beginnings of rills, and the runoff from them is a key part of the process of rill erosion.