River processes and Pressures Flashcards
What happens to the gradient of a river as you go away from the source?
The gradient becomes shallower
What happens to discharge as you go down a river away from the source?
The discharge start small and becomes very large towards the lower course
What happens to the depth of the river as you go down it away from the source?
The Depth Becomes deeper
What happens to the Channel shape as you go down a river away from the source?
The shape begin to narrow with steep sides in the upper course. Then in middle course it becomes flat with steep sides. In the lower course it becomes a flat floor with gently sloping sides.
What happens to velocity as you go down the river wey from the source?
It starts off quite fast and towards the lower course is very fast
What happens to the valley shape as you go down a river away from the source?
It starts with steep sides and then toward the lower course has gently sloping sides.
What are the features of the upper course?
There are waterfalls and interlocking Spurs.
What are characteristics of the middle course?
Meanders and floodplains
What are characteristics of the lower course?
Meanders, floodplains, levees and oxbow lakes
What are interlocking Spurs?
Interlocking spurs are ridges and Valleys sides which meet together with the opposite Valley.
How do waterfalls cause erosion?
- they are bands of more resistant rock that lay over less resistant rocks
- the water pours over the edge into a plunge pool which causes erosion undercutting the hard resistant Rock
- This erosion causes a overhang to form
- after a while the overhang can no longer be supported hence the harder rock collapses.
What are meanders?
Bends in the rivers’ course
How are oxbow lakes created?
This is where meanders form and the neck of the meander narrows, eventually cutting off and forming an oxbow lake
On a corner of a meander what side does erosion happened and what side does deposition occur?
Outer - faster = erosion
Inner - slower = deposition
How are levees formed on a river?
As the water floods over the bank of the river the water does not have enough energy to carry larger silt particles. As a result the silt build-up causing levees to form.
What is a delta and how is it formed?
A delta is formed when the water in the River slows down as it approaches the mouth this is normally where the ground is flat causing the channels to fill up with sediment and the river splits and spreads into many different streams
What are the impacts of climate on River landscapes and sediment load?
Erosion rate, transportation rate, weathering and amount of discharge.
How does climate have an effect on a erosion rate?
In wetter climates there is generally more erosion as more water enters the river through rainfall
How does weathering become affected by climate?
Weathering can be caused by fluctuation of temperature e.g. freeze thaw
How can climate impact transportation rate?
In wetter climates transportation is greater.
How is amount of discharge affected by climate?
In what a climates discharge is greater hence there is a higher transportation rate
What is the equation for discharge of a river?
Area x velocity
What are the two types of slope processes that are caused by rivers?
Soil creeping and slumping
What is soil creeping?
Particles of soil slowly move down the sides of Valleys under the influence of gravity
What is slumping?
When valley sides are eroded by Rivers making them steaper and more prone to downward movement
On a hydrograph what does the line represent?
Discharge
On a hydrograph what is lag time?
The difference in time between the peak of the rainstorm and the peak of the River discharge
What physical factors that cause lag time to shorten and limbs to be steep?
- Soil type - impermeable soils absorb less water
- geology - more resistant rock will absorb less hence more run off
- vegetation - less = more run off
- slope - steeper
- drainage basin shape - wide with lots of tributaries - water enter river quicker
- anticedent conditions - more saturated with water prior to storm
What human activities contribute to flooding?
Urbanisation, land use change, deforestation and building on floodplains
When were the Tewkesbury floods?
2007
What physical causes of flooding affected the Tewkesbury floods?
- the River Severn went through mountains and hills at source to increase surface run off
- west of UK usually experiences heavy rainfall
- 2 of the largest rivers in the UK meet in Tewkesbury - Severn + Avon
- also contributes to the discharge of the River Severn