What is a rill? Wikipedia says:
In hillslope geomorphology, a rill is a shallow channel (no more than a few tens of centimetres deep) cut into soil by the erosive action of flowing water. Similar but smaller incised channels are known as microrills; larger incised channels are known as gullies.
Artificial rills are channels constructed to carry a water supply from a distant water source. In landscape or garden design, constructed rills are an aesthetic water feature.
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