Confluence- point where tributaries meet the main channel
As more tributaries join the river gets wider, deeper and has a lower gradient.

When in the upper course the river erodes downwards (V-shaped valley formed), in the middle course the slope decreases and the energy is used to carry the material eroded & erodes laterally, then in the lower course the river deposits load due to decreased gradient.

The velocity of the river is determined by the amount of water touching the river's bed and banks, if the river is deeper there is less contact so there is less friction and a greater velocity.

Water takes the easiest course wo when eroding vertically in the upper course it follows softer rock, between barriers of more resistant rock- as this continues interlocking spurs are formed.

Hydraulic action and splash back undercut the soft rock further which causes the process to repeat, gradually the waterfall moves further upstream leaving a steep sided gorge.

The outside of a meander bend has the deepest water so this is where the most erosion takes place and forms a river cliff. Water moves more quickly on the outside due to the lack of friction, deposition occurs on the inside where water is slower/shallower making a slip off slope.