CHANGING CHANNEL CHARACTERISTICS- Other changes

Further changes

The shapes of the channel - influences the velocity of the river. 

 Upper course=  narrow + uneven channel - the presence of large boulders= large wetted perimeter. 

 Wetted perimeter = total length of the river bed + banks in cross section that are in contact with the water in the channel.

River levels = rise - heavy rain / snowmelt - upper course = relatively shallow. 

Large wetted perimeter=amount of water in the river= more friction.

Friction results = energy loss = slowed velocity.

Channels = larger + smoother- middle and lower course = more efficient. 

Wetted perimeter= proportionately smaller - volume of water flowing in the channel=less friction to reduce velocity. Mountain streams = slower velocity= energy is expanded overcoming friction on the uneven channel bed in the upper course- in the lower course = little to disrupt water flow

Hydraulic radius = cross-sectional area of the channel / wetted perimeter

A high hydraulic radius = river is efficient= moving water =loses proportionately less energy in overcoming friction - than when the ratio between cross-sectional area + the wetted perimeter = low. 
Larger channels = more efficient= area increases to a greater degree than wetted perimeter.