spread out, wide
氾 centers on spreading out widely, like water overflowing and covering a broad area.
氾 combines 氵 (water) with 㔾, which likely contributes the sound and suggests spreading or overflowing. The exact historical development is uncertain.
Water 氵 spreads out widely, like a flood covering the land. The right side 㔾 looks like a container being filled and overflowing.
For ハン, imagine a wide hand spreading water: hand -> ハン, and the water spreads out from your palm.
overflowing; flood; inundation; deluge
flooding within the confines of a levee (i.e. caused by surface runoff, drainage failure, etc.)
flooding caused by overflowing of rivers (e.g. breaching levee banks)
flood plain
flooding caused by overflowing of rivers (e.g. breaching levee banks)