Chapter 1 - Rivers Flashcards
What is the name for where a river begins?
The source
What are tributaries?
Smaller rivers that join to the main river
What is the watershed?
Imaginary line that separates two drainage basins
What is the point where two rivers join called?
Confluence
What is a river long profile?
A profile that shows a rivers gradient and how it changes as it flows from its mouth to the source
What is attrition?
When material in the river bumps into each other smoothing each other down into smaller particles
What is abrasion?
The process by which the bed and banks are worn down by the rivers load
What is hydraulic action?
The process by which the bed and banks of the river are eroded by the force of water against them
What is solution?
Chemicals, acids, dissolved in water slowly dissolve bed and banks
Which one erosion process in rivers has no effect on the bed and banks?
Attrition
Which one process of erosion does the load of the river not take part in?
Hydraulic action
What is channelisation?
Channelisation is where the banks and bed is man made to allow less friction therefore speeding up water flow, however it causes more flooding downstream
Name flood management methods
Channelisation, flood relief channels, flood warning systems, retention ponds, dams, doing nothing, afforestation, levees/embankments, floodplain zoning
What are retention ponds?
Allows run off to be temporarily stored therefore lessens the risk of flooding,however this takes up a lot of room and only holds a little water
What are dams?
Large concrete walls built to control discharge in a river meaning water can be held back and released in a controlled way, however this means more severe flooding upstream
What is a flood warning system?
Allows early warnings to evacuate areas of flood risk and therefore reduce damage and warn people on advance
What is a flood relief channel?
A built/dug our channel which allows water to bypass the main channel during times of flooding meaning more floodplain land is needed but main channel remains untouched
In hydrographs what is the bar and what is the line?
The bar is the rainfall, the line is the temperature
What is afforestation? How does this help prevent flooding?
Afforestation is the planting of new trees, by doing this around rivers the trees intercept rainfall meaning it takes longer to get to the river meaning it doesn’t rise so rapidly and the roots absorb some of the water meaning less enters the river
What are levees/ embankments?
They increase the potential maximum area of the river channel allowing it to hold more water before bursting its banks
What is floodplain zoning?
Considering where to build things and trying to avoid important property on areas that is likely to be flooded. Basically use common sense
What does a rivers cross profile show?
How a river changes as it moves from upper to lower course as a result in changes of the rivers energy, different features
What is the discharge? What is its equation?
The amount of water flowing through the river.
It’s the CSA (cross sectional area) x velocity
CSA = depth x width
So it is the same as width x depth x velocity
Which course has the least energy? Therefore the highest is …
The upper course has the least energy, the lower course has the most
Where is Sediment deposited in the upper course? Middle course? Lower course?
UC is on river bed
MC is on inner bend of meanders and on flood plains
LC is at the rivers mouth
What is the most dominant transportation at each course?
UC is traction, not much other sediment around
MC is saltation, although it is a mix and load has been eroded and there is more energy
LC is suspension, it’s been eroded a lot and is carried in the water, often making the water seem murky
How is a V shaped valley formed?
The river erodes downwards then the sides of the river are weathered and the rocks are pulled down by gravity over time into the river and taken away by the river, over time the rocks are eroded away leaving a v shaped valley
What must the rock be like on a river bed for a waterfall to form ?
There must be soft rock underneath hard rock
How does a waterfall form?
The hard rock is undercut and apt he soft rock underneath it is eroded, this then forms a plunge pool, the hard rock then falls due to gravity and creates a step. This step keeps occurring and getting larger and over time recedes
What is a gorge?
The cut in the Earth where a waterfall has eroded it/ receded, where their make their way upstream
When does a waterfall stop receding / eroding?
When it meets hard rock on hard rock and there is no soft rock to erode
What is capacity?
Maximum amount of things a river can carry/ hold
What is competence?
The largest seized individual particles a river can carry, the kargest rock it can move
How do small natural levees form?
Heaviest material is deposited first nearest the river bank when the river speed slows, this then builds up to form a small natural levee
What is an estuary?
The tidal part of a river where fresh water from the river merges from saltwater from the sea
What is the thalweg?
The fastest direction of flow in a river (the fastest route), such as in a river meander this is around the outside bend
