dredge, drag, clean
浚 centers on clearing out unwanted material from a waterway: dredging a channel, dragging the bottom, or cleaning out accumulated debris.
浚 combines 氵 (water) with 夋, which likely contributes the sound and may relate to the idea of moving or clearing. The exact historical development of 夋 is uncertain.
Water 氵 flows beside 夋, a shape that suggests movement and clearing. Picture a dredging machine dragging the riverbed, pulling up mud and debris to clean the channel.
For シュン, imagine a dredging boat making a shun sound as it drags the river bottom: shun -> シュン, and the water is cleaned.