The figurative usage "to be irrigated" may well be due to Akkadian; see CAD Š/2 p. 215.
Given that what looks like a C form in CPA is found only in the late LN text and only as a participle, it is probably only an unusual late G form much as the G of the phonologically similar root škḥ becomes confused with C, although in that case it is a early and common Aramaic development.