This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瀀 combines 氵 (water) with 憂, which likely contributes the sound. The exact historical development and original meaning are uncertain.
Water 氵 beside 憂 suggests a deep or abundant flow, but the exact meaning is unclear.
For ユウ, imagine a gentle 'you' sound echoing over water: you -> ユウ, as if the water is calling out.