Comp 2 Topic 4 - River Processes And Pressures Flashcards
What is the path of a river called as it flows downhill?
Its course
What are the different courses of a river?
Upper course (closest to the source of the river) Middle course ( in the middle) Lower course (closest to the mouth of the river)
What does the shape of the valley or channel tell you about the river?
Whether the river is eroding more or depositing more sediment.
What is the long profile?
Shows you how the gradient changes over the course
What is the cross profile of a river?
Shows you what the cross section of a river looks like
What are the characteristics of a river in the upper course?
The gradient is steep
V-shaped valley, steep sides, narrow, shallow channel
What are the characteristics of a river in the middle course?
The gradient is medium
Gentle sloping valley sides, wider, deeper channel
What are the characteristics of a river in the lower course?
The gradient is gentle
Very wide, almost flat valley very wide, deep channel
What is vertical erosion and where does it happen most frequently?
It deepens the river valley and channel making it V shaped.
It happens most frequently in the upper course of the river.
High turbulence causes rough pieces of rock and sediment to scrape the bottom of the river bed causing intense downward erosion
What is lateral erosion and where does it happen most frequently?
This widens the river valley and channel During the formation of meanders
Its dominant in the lower and middle courses
Describe the river Eden’s upper course
- The source is 600m above sea level in an area of hard, resistant rock.
- The valley is steep sided due to vertical erosion, the channel has a steep gradient.
- The river channel is narrow and shallow, meaning discharge is slow. The velocity is low due to the rough channel sides and bed.
- The river carries large angular stones.
Describe the river Eden’s middle course
- The middle parts of the river are made from sandstone which is easily eroded, it means that the river is wide due to lateral erosion.
- The gradient and sides of the river are less steep
- the river channel also becomes wider and deeper
- Discharge increases as more streams join the main river (tributaries)
- The river has smaller rounder rocks through erosion
Describe the river Eden’s lower course
- In the lower course the valley is very wide and flat
- By the time the river reaches carlisle it is only a few meters above sea level
- The river has a high velocity because theres very little friction from the channels smooth sides
- It has a very large discharge because two other rivers join the eden
- The river in carlisle is nearly 50m wide, very wide and deep
- material carried by the river is very fine and well rounded
How does weathering shape river valleys?
Weathering breaks down rock on valley sides.
Freeze thaw happens when temperature fluctuates above and below zero degrees c
Repeated freeze thawing widens rivers by breaking the sides down
What are the 4 types of erosion and what do they do?
Hydralic action- the force of the water breaks rock particles away from the river channel.
Abrasion- eroded rocks scrape the sides and bed of the river, this is the most common form of erosion
Attrition- eroded rocks picked up by the river smash into each other and break into smaller fragments. Their edges get rounded off as they rub together. Attrition causes particle size to decrease in the course.
Solution- river water dissolves some types of rock (chalk and limestone)
What are the 4 types of transportation?
Traction
Saltation
Suspension
Solution
What is traction?
Large particles like boulders are pushed along the river bed by the force of the water
What is saltation?
Pebble sized particles are bounced along the river bed by the force of the water
What is suspension?
Small particles like silt and clay are carried along by the water
What is solution?
Soluble materials dissolve in water and are carried along
What is deposition?
It is when the river drops eroded material it is carrying, It happens when the velocity of a river reduces.
The reasons this could happen include:
-The volume of water in the river falls
-The amount of eroded material in the river increases
-The water is shallower
-The river reaches its mouth
How are waterfalls and gorged formed?
1) They are formed where are river flows from an area of hard to soft rock
2) The softer rock is eroded ore than hard rock creating a step in the river
3) The step gets bigger through repeated erosion
4) A steep drop is eventually created
5) The hard rock is eventually undercut, becomes unsupported and collapses
6) The collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rocks by abrasion, it creates a deep plunge pool
7) Over time more undercutting causes more collapses, the waterfall will retreat leaving behind a steep sided gorge
What are interlocking spurs?
In the upper course most erosion is lateral creating steep v shaped valleys
The rivers don’t have enough power to erode laterally so they wind around hills that stick out in their way
The hillsides that interlock as the river flows between them are called interlocking spurs
How are meanders formed?
Rivers develop meanders in the middle and lower course in areas of deep and shallow water.
1) The current is faster on the outside of the bend because the river channel is deeper (less friction)
2) More erosion (abrasion and hydraulic) take place on the outsides forming river cliffs
3) The current is slower on the inside of the bend because the river channel is shallower (more friction)
4) Eroded material is deposited on the inside bend forming slip off slopes.
How are Ox-bow lakes formed?
1) Erosion causes the outside bends to get closer until theres only a small bit of land between the bends (neck)
2) The river breaks through the neck usually during flooding and the river flows along the shortest course
3) Deposition eventually cuts of the meander forming an ox-bow lake
What is a flood plain?
It is wide valley floor either side of the river which occasionally gets flooded
When the river floods the floodwater deposits sediment and eroded material in the flood plain making it higher
Menders migrate across the flood plain, making it wider
The deposition that happens on slip off slopes also builds up the flood plain
What are levees?
They are natural embankments along the edges of a river channel.
During a flood, eroded material is deposited over the whole flood plain.
The heaviest material is deposited Closest to the river channel.
Over time the levees build up
What is a delta?
Rivers are forced to slow down when they meet the sea or a lake, It causes them to deposit material they are carrying
If the sea doesn’t wash it away it builds up and the channel gets blocked
It forces the river to split into little channels called distributaries.
Eventually the material builds up so much that low lying areas called deltas are formed
Identifying river landforms on a map
See page 65
How is river landscape and sediment load influenced by climate?
1) Rivers have a higher discharge in wet climates due to rain
2) Higher discharge means more erosion. The higher the volume of water the more power it has to erode. It adds more material to the river.
3) It creates V shaped valleys in the upper course and Wide flat flood plains in the lower course.
4) Transportation also increases as the river has more energy to carry material
5) Weathering like freeze thaw can increase sediment load and can affect the shape of the landscape
How is river landscape and sediment load influenced by Geology?
- Rivers flowing through areas of hard rock have a smaller sediment load becase the rocks have a slower rate of erosion.
- Areas with soft rock will experience more erosion , the rivers have a higher sediment load
- Areas with hard rock will have steep valley sides
- Areas with soft rock will have gentle sloping valley sides
- Waterfalls when there is hard rock on top of soft rock
- Interlocking spurs are formed when soft rock is eroded before the hard.
How is river landscape and sediment load influenced by slope processes?
1) Valley sides are steeper increasing movement of material down the slopes through vertical erosion
2) Mass movement can add large amounts of material to the rivers load, more likely in cold or wet weather
3) soil creep is when soil particles move due to gravity
It as caused by the expansion and contraction of the soil
Water adds weight and It moves down the slope
It dries out and contracts
It can add lots of fine material to the river
What is the peak discharge in a hydrograph?
The highest discharge in the period of time your looking at.
What is the Lag time in a hydrograph?
The delay between peak rainfall and peak discharge
What is the rising limb in a hydrograph?
The increase in river discharge as rainwater flow into the river.
What is the falling limb in a hydrograph?
The decrease in a rivers discharge as the river returns to normal levels
What is a hydrograph?
They show the changes in river discharge around the time of a storm. Its measured in cubic meters per second m3/s
How does Geology affect hydrographs?
Water cant infiltrate into impermeable rocks, so theres more runoff
how does Soil type affect hydrographs?
More impermeable soils cant absorb as much water as soil, which increase runoff. Shallower soils also become saturated more quickly than deeper soils.
how does Slope affect hydrographs?
The steeper the slope, the less infiltration and the higher the runoff
how does Drainage basin type affect hydrographs?
Circular drainage basins have a shorter lag time and higher discharge than narrow basins because water reaches the main channel at the same time. In a narrow basin the water take a long time to reach the river
how does Antecedent (previous) conditions affect hydrographs?
Previously wet or cold weather can increase runoff as water cant infiltrate saturated of frozen soil
how does Urbanisation affect hydrographs?
Water cant infiltrate into concrete and tarmac so more water is runoff into gutters and drains which is transported to rivers increasing discharge and reducing lag time
how does Deforestation affect hydrographs?
Trees take up water from the ground and store it which reduces runoff. Cutting down trees increases runoff and causes more water to enter the river channel, which increases discharge.
What physical factors are causing River Eden to be prone to flooding?
- The climate in that area is mild and wet
- its one of the wettest parts of the uk often experiencing intense rainfall
- The eden basin is surrounded by areas of impermeable rock such as the pennines and lake district. More water runs off into the river channel.
- snowfall is common during the winter months adding more water to the river in a short space of time.
What Human factors are causing River Eden to be prone to flooding?
- Carlisle is a built up area and there has been a lot of development on Edens flood plain. It has impeded the flood plains to absorb and store floodwater. Little infiltration means more runoff.
- natural woodlands have been cleared in the area so there is more surface runoff
- Parts of the Eden valley have been drained to make them more suitable for farming. Drainage ditches then flow directly into the river channel.
Why and how did Carlisle flood on the 5 and 6th of December 2016?
Previous conditions- soil saturation and discharge was high due to wet weather in summer
Rainfall- more than 3m fell in less than 24hrs. Highest in UK ever.
Short lag time- The water across the drainage basin quickly reached the main channel
Blockages- debris blocked the river forcing it to spill over
Bad drainage-runoff from impermeable surfaces flooded the river.
How is the risk of flooding in the UK being increased by the increased frequency of storms?
1) Frequency of storms in UK increasing
2) It is thought that storms are becoming more extreme-more intense rainfall is increasing scale of flood events.
3) ground is more saturated so flooding is more likely
How is the risk of flooding in the UK being increased by Land use change?
- as UK population increases mean more impermeable surfaces and more rapid surface runoff.
- Removing plants mean more goes into the river than being absorbed.
- More building is being done on flood plains which are prone to flooding.
- More people living on flood plains mean that there are more people at risk of flooding if flood defences fail.
How is flooding a threat to people?
1) People can be killed or injured by floodwater
2) roads, bridges and rail lines can be damaged or destroyed
3) Possessions can be damaged or washed away
4) People can become homeless
5) Business may be forced to shut down because of flood damages and disrupted power lines (loss of livelihood)
How is flooding a threat to the environment?
1) contaminated floodwater can kill animals and pollute rivers
2) farmland can be ruined due to the deposition of silt and sediment
3) River banks are eroded causing huge changes to river landscape. Widening of the river channel, increased deposition downstream.
4) The force of floodwater can uproot and drown trees and plants
What is soft engineering (rivers)?
Schemes set up using knowledge of a river and its processes to reduce the affects of flooding
What is hard engineering (rivers)?
Man-made structures built to control the flow of rivers and reduce flooding
What are the benefits and costs of Flood walls?
They are barriers built along the river banks
They increase the height of the river banks
The river can hold more water
But they are very expensive
Unsightly and can block river view
What are the benefits and costs of embankments?
They are high banks of soil or natural materials. They stop the river flowing into built up areas during a flood. The use of soil makes them more attractive.
They are quite expensive to build and there’s a risk of severe flooding if the water exceeds the height of the embankment or it breaks.
What are the benefits and costs of flood barriers (floodgates)?
They are built on river estuaries to stop flooding from storm surges or very high tides. They can be shut when reports of storm surge or high tides are announced.
Floodgates are very expensive and need to be maintained regularly
What are the benefits and costs of flood barriers (demountable)?
They provide temporary protection against flooding. They don’t spoil the scenery.
They are expensive and are only put up when there is a forecast so there is a chance they aren’t put up in time
What are the benefits and costs of flood plain retention?
It involves maintaining the rivers flood plain by not building on it. It slows floodwaters and allows the floodplain to do the job of absorbing the floodwater.
No money needs to be spent
But it cant be used in urban areas
What are the benefits and costs of river restoration?
It involves making the river more natural by removing man made structures. The river is left in its natural state so very little maintenance is required
There is local flooding risk and can cause major flooding
