Though both stems end in an unvoiced stop consonant, nak– doesn't have a nasalized future, whereas (en)quat– does. Did Tolkien elaborate on that or give more examples of the latter Root Verb type anywhere?

+ܤܡܝ ܦܠܕܢܝܘܤ it appears that quat- and quanta- are transitive/intransitive variants of the same root, so "the riverbed will refill with water after rain" would be i ratta enquatuva nenen nennen pó ulo:

eldamo.org - Eldamo : Quenya : quanta-

+Tamas Ferencz I see. Thank you.