Topic 4 UK Rivers Flashcards
What is discharge
The volume of water flowing in a river at one particular point and time
What is the course
The path of a river as it flows downhill
What are features of the upper course
Steep gradient. V-shaped valley, steep sides, shallow channel
What are features of the middle course
Medium gradient. Valley sides wider, deeper channel
What are features of lower course
Low gradient. Very wide valley, deep channel.
Where does vertical erosion mainly take place
Upper course of the river
Where does lateral erosion commonly occur
Dominant in the middle and lower courses of river
What is traction (transportation)
Large particles are pushed along the river bed by the foce of water
What is suspension (transportation)
Small particles like silt and clay are carried along by the water
What is saltation (transportation)
Pebble-sized particles are bouncing along the river bed by the force of the water
What is solution (transportation)
Solube materials dissolve in the water and are carried along.
What is deposition
When a river drops the eroded material its transporting
What does antecedent conditions mean
Pre-existing conditions
In what course are waterfalls mostly found in
The upper course
How are waterfalls formed
The softer rock is eroded more than the hardrock creating a ‘step’. This gets erodedmore and more until a steep drop is then created. This is called a waterfall. The hardrock is eventually undercut by erosion and collapses. The collapsed rocks are swirled around at the foot of the waterfall and erode the softer rock by abrasion creating a plunge pool. Overtime more undercutting causes the waterfall to retreat leaving a steep-sided gorge
How are interlocking sours created
In the upper course of the river most of the erosion is vertically downwards. The creates steep-sided v-shaped valleys. They arent powerful enough to erode laterally so they have to wind around the valleys. The hillsides that interlock with eachother are called interlocking spurs
What are meanders
Large bends in rivers commonly found in middle to lower courses of the river
Describe the erosion of a meander
The current is faster on the outside of the bend because the river bend is deeper and less friction to slow the water down. Therefore more erosion takes place on the outside of the bend causing river cliffs. The current is slower on the inside of the bend because the river channel is shallower, more friction to slow down water. So eroded material is deposited on the inside of the bend causing slip off slopes
How are ox-bow lakes formed
When meanders get larger over time - they can eventually turn into an ox-bow lake. Erosion causes the outside bend ti get closer until there is only a small bit of land left between the bends. The river breaks through this land. And the river flows along the shortest course. Deposition eventually cuts off the meander creating an ox-bow lake.
What are flood plains
The wide valley floor on either side of a river which ocassionally gets flooded
What are levees
Natural enbankments (raised bits) on the edges of a river channel
How are deltas formed
Rivers are forced to slow down when coming across a sea or lake. This causes them to deposit the material that theyre carrying. The sea doesnt wash it away and this builds up intil low lying areas of land is being built up called deltas
What climates cause a higher discharge
Wetter climates
What does a higher disharge cause
An increased rate of erosion because if w river has a higher volume of water it has more power to erode river banks. Also an increase in transportation as it has more energy to transport material
What is lag time in a storm hydrograph
The delay between peak rainfall and peak discharge
What is the rising limb in a storm hydrograph
The increase in river discharge as rainwater dlows into the river
What is the falling limb in a storm hydrograph
The decrease in river discharge as the river returns to its normal level
What is lag time and how does it happen
Lag time happens becausw most rainwater doesnt land directly in the river chanel. There is a delay as rainwater gets to the channel. The rainfall gets to the channel by surface run off, soaking into the ground and flowing underground
What happens if more water flows as the runoff in a hydrograph
The lag time will be reduced. Meaning the discharge will increase and the hydrographbwill be steeper because more water gets to the river in a shorter space of time.
How does geology and soil type affect the shape of a hydrograph
If there are impermeable rocks, water wont be able to infiltrate (soak into the ground) causing more runoff making the rising limb more steep
How does urbanisation affect a storm hydrograph
With an increase in infastructure, there will be more impermeable surfaces usch as concrete so there is more runoff, gutters and drains quickly take runoffs to rivers which rapidly increase discharge
How does a flood happen
When the level of a river gets so high it spills over its banks onto the flood plain
How does deforestation increase chances of flooding
Removing vegetation and permeable surfaces mean that water that would have been stored in soil or plants and trees now flows quickly downstream
Give 4 ways river flooding threatens people
People can be killed or injured by flood water
Roads,bridges and rail lines can be damaged or destroyed
Floodwater is can contaminate with sewage leading to a lack of clean drinking water
People can be made homeless as their houses are damaged or destroyed
How can flooding create threats to the environment 4 ways
Flood water contaminated with sewage or rubbish can pollute rivers which can damage wildlife habitats
Farmland can be ruined by sediment being deposited after a flood
River banks are eroded which widens the river channel and increase deposition downstream
The firce if rainwater can uproot trees and plants
What are the two types of strategies to deal with flooding
Hard engineering
Soft engineering
What is hard engineering
Man made structures built to control the flow of rivers and reduce flooding
What is soft engineering
Schemes set up using knowledge of a river and its processes to reduce the side effects of flooding
What are 4 examples of hard engineering for river management
Flood walls
Embankments
Flood barriers (flood gates)
Flood barriers (demountable)
What are flood walls, are they expensive, effect look of environment?
Artificial barriers built along river banks. Theyre designed to increase the height of the river banks, allowing the river channel to hold more water. They are very expensive and can block the view of the river
What are embankments. Are they expensive, do they effect the view of the environment
High banks built along or near the river banks. Prevents water from reaching flood plain. They can be made from earth or other natural materials making them less unsightly than flood walls. Quite expensive to build and severe risk of flooding if water rises above the level of the embankments
What are flood gates, are they expensive
Built on river estuaries (where rivers meat the seas) to stop flooding from storm surges or very high tides. They can protect a very large area of ground however wre very expensive and need to be maintained regularly
What are demountable flood barriers, what do they do
They provide temporary protection against flooding and only put up when theres a flood forecast. Therefore a risk they wont be put up in time. They are quire expensive to build but dont spoil the look of attractive locations
What are two exampkes of soft engeneering strategies
Flood plain retention
River restoration
Explain what flood plain retention is
Maintaining the rivers flood plain by not building on it. It helps slow flood wtaers down and maintain the flood plains ability to store water. Costs no money but cant be used in urban areas
Explain river restoration, maintanance?negatives?
Involves making the river more natural so the flood plain can flood naturally. Discharge is reduced so less chance of flooding downstream. River is left in natural state so little maintanance required.
However this can cause local flooding especially if nothing is done to prevent majour flooding
