The same gravitational force that keeps you from floating into space.
gravity
Rivers are positioned on hills, or uneven land. The rivers run downhill, so the water goes in that direction.
No
Downhill.
All streams including rivers run downhill, so melting snow, rain, etc. produce water and this water drains into rivers and the rivers run downhill until they empty into a larger river or a major body of water like a gulf or ocean.
North and south do not mean up and down. Rivers always run downhill. In the case of some rivers, downhill is to the north.
Simply, always downhill, under gravity, its course influenced by the geology of the land it crosses.
Gravity, rivers flow downhill
Downhill.
In Virginia most rivers run downhill. Or: The water in most Virginia rivers is wet. Or: Fish live in Virginia's rivers. Or: The mouth of Virginia rivers is at a lower elevation then the source. Or: No recorded Virginia river runs uphill. Or:
As with all rivers the Nile cannot defy gravity and therefore flows 'downhill'.
Bears Can't Run Downhill has 288 pages.
They are wetThey flow downhill