waterfall, rapids, cascade
瀧 centers on rushing water descending steeply: a waterfall, rapids, or cascade. The core idea is powerful, fast-moving water.
瀧 combines 氵 (water) with 龍 (dragon), likely suggesting a dragon-like torrent of water. The character is the older form of 滝, which is now the standard simplified form in Japanese.
A dragon 龍 rising from the water 氵 creates a massive splash—a waterfall or cascade of rapids.
For ロウ, imagine a low, rumbling roar as the dragon-waterfall crashes down: low -> ロウ.