dam, prevent, stop up
堰 centers on blocking or holding back a flow, especially water: a dam, or the act of preventing something from passing. The idea of stopping up is a direct physical application of that same blocking action.
堰 combines 土 (earth) with 匽, which likely contributes the sound and carries a sense of blocking or damming. The structure suggests an earthen barrier that holds back water.
The left side is earth 土, and the right side 匽 looks like a barrier with something enclosed inside. Picture an earthen wall built across a river to dam the water and stop it up.
For エン, imagine the dam ending the river's flow: end -> エン, and the earthen wall stops the water completely.
dam; weir; barrier; sluice
dam; weir
canal gates; river gates
earthfill dam
gushing forth; bursting out; like breaking a dam
to break a dam; to burst out
damming (e.g. a pond)
sheeting; sheathing board; cover
dammed lake (formed by natural damming of a river, esp. by landslide, volcanic eruption, etc.)