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Flashcards in Long Profile Deck (18)
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What is long profile

The height of the channel floor from source to mouth


What is the channel cross profile like in the upper course

Narrow and uneven, because of the presence of deposited boulders.
Rectangular shapes banks.


What is the channel cross profile like in the middle course

It starts to meander, the channel becomes asymmetrical on the river bends but mainly smooth and symmetrical on the straight stretches


What is the channel cross profile like in the lower course

It widens and deepens, banks of deposition and eyots (islands of deposition) can disrupt the shape of the channel cross section, leading to a braided channel. Levees can also form.


What does the shape of the channel influence

The velocity of the river


What is wetted perimeter

The total length of the river bed and banks in cross section that are in contact with the water in the channel


What is the wetted perimeter like in the upper course

The channel is narrow and uneven due to the presence of large boulders so there is a large wetted perimeter


When is there more friction

When there is a large wetted perimeter in relation to the amount of water in the river


What does friction result in

Energy loss and the velocity of the river slows


When are rivers most efficient

In the middle and lower course as the channels are larger and smoother; the wetted perimeter is proportionately smaller than the volume of water flowing through the channel (less friction to reduce velocity)


Why is velocity slower in the upper course

Because so much energy is expended over coming friction on the uneven channel bed in the upper course, whereas in the lower course there is little to disrupt water flow


What is hydraulic radius

The channel shape


How is hydraulic radius calculated

Cross sectional area of the channel / wetted perimeter


A high hydraulic radius =

More efficient river (because the moving water loses proportionately less energy in overcoming friction than when the ratio between the cross sectional area and the wetted perimeter is low).


How efficient are larger channels

More efficient; area increases to a greater degree than wetted perimeter


What does a long profile of a river illustrate

The changes in the altitude of the course of the river from its source, along the entire length of its channel, to the river mouth


What shape is the long profile

Smoothly concave, with the gradient being steeper in the upper course and becoming progressively gentler towards the mouth


What is the channel cross profile (section)

A view of the river bed and banks from one side to the other at any one point on its course