wide expanse of water
淼 centers on a vast, seemingly endless stretch of water, like an ocean or great flood. The single given meaning is a wide expanse of water.
淼 is formed by tripling the water radical 水, a common Chinese character formation pattern used to intensify the meaning of vastness or abundance. The exact historical development is uncertain, but the tripled structure strongly suggests an emphasis on a great expanse of water.
Three 水 (water) components stacked together: imagine water upon water upon water, stretching endlessly in every direction. That overwhelming amount of water is a wide expanse.
For ビョウ, picture a vast ocean where a buoy (ビョウ) bobs alone on the endless water: buoy -> ビョウ, and the buoy marks the wide expanse.