we all know liquids (in this case water) flow from high pressure to low pressure or from high altitude to low altitude .. read more
You can see the flow of 3 major himalyan rivers : Ganga, Indus and Brahmaputra.Neither of them follow this south east flow. But Krishna and Godavari river of indian peninsula flow towards south east due to inclination of peninsular land mass towards south east. so. IT IS THE INCLINATION OF THE LANDMASS WHICH DECIDES THE DIRECTION OF FLOW OF RIVERS. read more
Ps: Chenab and others flow westwards from Himalayas. Ganges in actual starts from south east to north west before bending towards east. Gradient plays an important role as simple as water when spilled on floor. read more
It flows along the northern slope parallel to the Himalayas towards the east for about 1,200 km as Tsangpo River. After making a sharp bend towards the south, it enters into India through a deep narÂrow gorge in the east of Namcha Barwa in Arunachal Pradesh as the Dihang. read more