Does ideal river velocity increase/decrease further downstream?
Velocity increases further downstream. This is because upstream, rivers start in mountains or hills, which are made up of harder rock, so is harder to erode. This means the river is narrower and the river bed is rougher. This will mean more friction from the colliding water particles, slowing velocity. This is why further upstream river flow is more turbulent. Further downstream however, the rock is softer, so the river bed is much smoother, and the rivers are much wider. This means that there is plenty room for water particles to move and they are not being shaken up by a rough river bed. So less collision between water particles means less friction and so an increase of velocity.
