Because the Width and Depth both increase downstream. This means the wetted perimeter will also increase.
steamboat
steamboat
Oars
All rivers that flow downstream are capable of producing hydroelectric power.
Oars
They reduce flow, and create a backpool which reduces flow downstream
Rivers carry silt downstream and build deltas.
Rivers carry silt downstream and build deltas.
No. The water flows downstream. Correction, I believe the Amazon flows upstream
soil flow
Since we have no idea what "this" might be, we can't answer the question properly.
The land between and around rivers, e.g. in the flood plains and deltas, is full of sediments and nutrients that were carried downstream.