במדבר כא:יט פירוש: רש״י, ספורנו, רבנו בחיי ודעת זקנים

וממתנה נחליאל — Understand this as the Targum does: And after it had been given them, it descended into the valley.

וממתנה נחליאל, in spite of this the waters neither increased nor decreased as a result of their behaving so erratically and having to traverse both depressions in the earth and hilly country.