Cross Profiles Flashcards
What is the cross profile of the upper course?
Vertical erosion, spurs, high valley sides.
What is the cross profile of the middle course?
Wide floodplain, lowered valley sides, spurs cut back to form line of bluffs, sediments below river, lateral erosion.
What is the cross profile of the lower course?
Wide floodplain, levées, bluffs, sediments below the river, oxbow lakes, flat valley sides, lack of erosion and reduced competence = large scale deposition.
What is valley cross profile?
The view of the valley from one side to another.
How and where can a braided channel occur?
In the lower course banks of deposition and eyots (islands of deposition) can disrupt the shape of the channel cross-section. Levées can also be formed (or man made created).
What does the shape of the channel influence?
The velocity of the river.
Where is the largest wetted perimeter?
The upper course (narrow and uneven due to boulders).
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.
A high hydraulic radius means that…
The river is efficient- because the moving water loses proportionately less energy in overcoming friction than when the ratio between the cross sectional area and wetted perimeter is low.
Are larger or smaller channels more efficient?
Larger; area increases to a greater degree than wetted perimeter.
How do you calculate hydraulic radius?
Cross sectional area of the channel / wetted perimeter
Define braided channels
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots.
Define velocity
The velocity of a river refers to the rate of water movement, often measured in metres per second. Mean flow velocity increases with distance from the source.
Define roughness
Channel bed roughness is a measure of how rough the bed of a river is. It can be calculated using Manning’s Roughness coefficient.
