淹 alone means 'to flood/submerge.' 淹没 (yānmò) is the more common compound meaning 'to inundate/submerge completely.' 淹死 (yānsǐ) means 'to drown to death.'
Left-side water radical, the three-drop form of 水. Anchors 淹 in the river-and-flood family - the verb means to drown, submerge, or steep something in liquid. Same indexing radical as 河 river, 海 sea, 溢 overflow, 浸 to soak.
Right side 奄 supplies the sound - yǎn → yān with tone shift. The 'cover, envelop' meaning of 奄 also reinforces the sense: floodwater suddenly engulfs and covers everything. Same phonetic appears in 腌 to pickle, 庵 hermitage, 掩 to shield.
