The Euphrates is obliged to conform the thrust of partner.

TCD MS 10516 folio 87 recto

TCD MS 10516 folio 87 recto

[12th October 1916] therefore compelled to change its bed under this pressure; it is being driven southward by the Tigris which, in its effect, might be considered as a large lateral affluent of the Euphrates. Thus the course of the Euphrates is here obliged to conform to the thrust of its more powerful partner. Its main stream is broken; it is divided into two smaller channels, one of which recieves the Tigris, the other is a more recent channel gradually developing some thirty miles to the south, while in between the channels is a complex sea of swamps and lakes and water-courses, the overflow that the thrust of the Tigris is forcing across the desert.
It seems usual for the course of a river winding through an alluvial plain to depend in some degree on the volume of its lateral affluents*.
*(1) Ganges: Geology of India (2) Tarim River.