waterfall
瀑 centers on a powerful, rushing waterfall. The core idea is a steep cascade of water, often with force and volume.
瀑 combines 氵 (water) with 暴, which likely contributes the sound and the idea of violent or sudden force, together suggesting a violent rush of water like a waterfall.
The water radical 氵 beside 暴 (which suggests violence or suddenness) creates an image of water crashing down violently: a waterfall.
For バク, imagine a waterfall crashing into a pool with a loud 'back' splash: back -> バク, as the water hits the rocks and echoes back.