Why does a river get narrower as it aproaches a waterfall?

Question

River Breamish - Linhope Spout, if this is any help. But you can give me any old example! This is what I am studying at the moment in college.

Answer 1

because wen u hit the cliff gravity pushes down so this suks the water and the current gets faster makin the river narrow.

Answer 2

my theory is that since there is an upcoming outlet for the water in the river to travel fast, and therefore there exists a high current zone, it doesnt need to spread in width (in a low current zone, the width of a river increases)

AM

Answer 3

This isn't a hard and fast rule as some rivers widen when they reach waterfalls - it all depends on the surrounding geology and the rate of retreat of the local rocks as the river erodes them. In the ones that do narrow it's mostly down to the fact that water flow rate increases so that the river cuts down vertically rather than spreading horizontally but again local geological conditions influence specific rivers. Hope this helps.