What does the cryptic crossword clue "Flow of excess water never blocking wading bird (3-3)" mean?

The wordplay uses a container (one word inside another). NO (synonym="never") in RUFF (synonym="wading bird") = RUNOFF The answer is RUNOFF.

Flow of excess water never blocking wading bird (3-3)

Independent Cryptic #11102 | 22 Across | 2022-05-13 flower