Answer:
The direction of rivers are usually expressed with respect to the directions we are familiar with: North, South, East or West.
A river has an origin, usually at a higher latitude and ends at the sea or ocean or a large water body. Gravity is the driving force for river flow. Hence, we gauge the ‘direction’ the water is going to flow for any river.
If we were going to get more technical, flow in rivers and streams are measured for their streamflow, which is the amount of water passing through some infinitesmal volume, i.e a point over time. The velocity of the water is determined using acoustic/Doppler based instruments, which will give the local direction of the flow of the river at the measured point along with the velocity.
Hope the answer helps!
