river in Hebei province
洨 is a specific proper noun: the name of a river in Hebei province. It has no broader conceptual center beyond this geographic reference.
洨 combines the water radical 氵 with 交, which likely contributes a phonetic element. It is used specifically as a river name.
The water radical 氵 beside 交 suggests a river crossing or intersecting the land, fitting its use as a river name.
For コウ, picture a river flowing through a cove: cove -> コウ, and the water radical 氵 reinforces the river image.
—