Why does velocity increase downstream?
Velocity downstream increases when there are more streams feeding the main stream. If the total volume of those side streams is bigger than the volume of the main stream, it means that water is “crammed” into the smaller area and has to flow faster. The same thing happens in our cardiovascular system – blood in the cappilaries flows slower than in arteries, because the total volume of the cappilaries is bigger than the volume of the artery they flow into.
