The most common and most likely answer to this crossword clue is the 5 letter word GULLY
I've seen this crossword clue in The Times
G
U
L
L
Y
Buddy explains!

The straight part
We know that "Channel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case channel = gully.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GULLY mean?
GULLY noun- A trench, ravine or narrow channel which was worn by water flow, especially on a hillside.
- A small valley.
- A drop kerb.
- A road drain.
- A fielding position on the off side about 30 degrees behind square, between the slips and point; a fielder in such a position
- A grooved iron rail or tram plate.
- To flow noisily.
- To wear away into a gully or gullies.
- (northern UK) A large knife.