River Processes And Pressures Flashcards
What do rovers form as the flow downhill?
Channels and valleys
What is the difference between and cross profile and a long profile?
Long- shows change of gradient over course
Cross - shows cross section
What is the valley and channel shape in the upper course?
V-shaped valley, steep sides.
Narrow, shallow rivers
What is the valley and channel shape in the middle course?
Gently sloping valley sides.
Wider, deeper channel
What is the valley and channel shape of the lower course
Very wide, almost flat valley
Very wide deep channel
How does freeze thaw weathering occur?
When water gets into cracks of rocks and freezes causing it to expand. When the water melts, releasing pressure on rock. Repetition of this in the rock eventually cause it to break up.
What is hydraulic action?
Type of erosion where force of water breaks rock particles away from river channel
What is abrasion?
Erosion where rocks picked up by river scrape and rub against channel, wearing it away. Most common type of erosion
What is attrition
Erosion where eroded rocks picked up by rover smash into each other and break into smaller fragments. Edges become rounded off as they rub. Further material travels means more eroded it gets
What is solution
Erosion where river water dissolves some types of rock eg. Chalk and limestone
What is traction
Large particles like boulders are pushed along river bed by force of water
What is saltation
Pebble sized particles are bounced along river bed by force of water
What is suspension
Small particles like slit and clay are carried along by the water
What is deposition
When the river drops the eroded material its transporting
Where do waterfalls form
Where a river flows from an area of hard rock followed by an area of soft rock
How do waterfalls form?
Softer rock is eroded creating a step in river. As water falls over step, more soft rock is eroded forming a steep drop which is a waterfall.
How are gorges formed
When hard rock from waterfall is undercut by erosion and collapses. Collapsed rocks swirl around at foot of waterfall to erode soft rock, creating plunge pool. More undercutting means more collapsing causing waterfall to retreat and forming a steep sided gorge
How do interlocking spurs form?
In upper course of river, the steep sided valleys mean rivers arent powerful enough to erode laterally so they wind round high hillsides that stick out into their paths on either side. The hillsides that interlock are interlocking spurs
How do meanders form
1 - current is faster on outside of bend as its deeper causing more erosion to occur on outside of bend, making river cliffs
2 - current is slower on inside of bend as river channel is shallower so eroded material is deposited on inside of bend - forming slip of slopes
How are oxbow lakes formed from meanders
1 - erosion causes outside of bends to get closer until only small bit of land is left between them (the neck)
2 - river eventually breaks through and flows along shortest course
3 - deposition eventually cuts off meander forming an oxbow lake
What are flood plains?
The wide valley floor on either side of a river which occasionally gets flooded.
What happens to a flood plain when the river floods?
When the river floods onto the flood plain the water slows down and deposits eroded material that its transporting, building flood plain up. Meanders migrate across flood plain, making it wider as well as migrating downstream, flattening out the valley floor. Deposition on slip off slopes builds up flood plains
How levees form?
Theyre natural embankments and during flood, the eroded material is deposited over flood plain. The heaviest material is deposited closest to river channel as it gets dropped first when rover slows. Over time, deposited material builds up, creating levees
What are deltas
Low lying area where a river meets the sea
How do deltas form?
Rivers are forced to slow down when they meet sea or lake. Causing them to deposit material that theyre carrying. If sea doesnt wash it away, then material builds up and blocks channel. Causing channel to split up into to distributaries (smaller rivers). Eventually so much material is built up that deltas form
How does climate influence river landscapes and sediment load?
Wetter climates have higher discharge
Higher discharge increases rate of erosion as river is more powerful, adding material to river load
Shapes landscapes by forming v-shaped landscapes and flood plains
Transportation increases with higher discharge as river has more energy to carry material
Weather increases sediment load and can affect shape of landscape
How does geology influence river landscapes and sediment load?
River flowing through hard rock areas have slower rate of erosion as rocks are more resistant
Areas of soft rock experience more erosion adding more material to rovers material
More resistant rock tend to have steeper valley sides
Less resistant rocks have gentle sloping valley sides
How do slope processes influence river landscapes and sediment load
Vertical erosion increases steepness of valley sides and increases movement of material down slopes
Mass movement more likely to occur during colder and wetter weather
Soil creep can add lots of fine material to rivers load
What is peak discharge?
The highest discharge in the period of time youre looking at
What is lag time?
The delay between peak rainfall and peak discharge
What is a hydrograph?
A graph to show the changes in river discharge around the time of a storm
What is the rising limb?
The increase in river discharge as rainwater flows into the river
What is a falling limb?
The decrease in river discharge as the river returns to its normal level
How does geology affect storm hydrographs?
Water cant infiltrate into impermeable rocks, so theres more run off
How does soil type affect storm hydrographs?
More impermeable soils cant absorb as much water as sandy soils, which increases run off. Shallower spils also become saturated more quickly than deeper soils
How does a slope affect a storm hydrograph?
The steeper the slope, the less infiltration and the higher the runoff
How does a drainage basin type affect a storm hydrograph?
Circular basin -shorter lag time and higher discharge than narrow basin because water reaches main river channel at same time
Narrow basins - water from far end of basin takes long time to reach main channel
How do antecedent affect s storm hydrograph?
Previously wet and cold weather can increase run off because water can’t infiltrate saturated or frozen soil
What are the human factors that affect a storms hydrograph?
Urbanisation - water cant infiltrate into impermeable so theres more runoff. Gutters and drains increase discharge
Deforestation - cutting down trees increases run off, as there are mo trees to absorb water, which increases discharge
Why is the risk of flooding increasing in the UK?
Increased frequency of storms - consequence of global warming, storms are becoming more extreme, more periods of wet weather make soil more saturated
Land use change - urban areas reduce water infiltration hence water cant go anywhere, lots of development on flood plains
How does flooding threaten people?
Can cause injury or death. Transport damaged. Can contaminate water supply. Loss of possessions and homes. Businesses destroyed
How does flooding threaten the environment?
Contaminated water can pollute rivers. Farmland can be ruined. Rapid erosion changes river landscapes. Can uproot trees and plants.
What are the hard engineering strategies to reduce the risk of flooding?
Flood walls, embankments, flood barriers (floodgates), flood barriers (demountable)
What are the soft engineering strategies to reduce the risk of flooding?
Flood plain retention, river restoration
What are the advantage and disadvantages of flood walls?
Increase height of river banks to allow river to hold more water
Very expensive and are unsightly and block view of river
What are the advantage and disadvantages of embankments?
High banks built along river banks
Stop river flowing into built up areas, protect buildings and infrastructure on flood plain, can be made from natural materials making them less unsightly than flood walls
Expensive, severe risk of flooding if fail
What are the advantage and disadvantages of flood barriers (floodgates)?
Eg. Thames barrier
Are built on estuaries to prevent flooding from storm surges or high tides. Can be shut when theres a surge forecast to protect large area of land.
Very expensive and need to be maintained regularly
What are the advantage and disadvantages of flood barriers (demountable)?
Provide temporary protection against flooding
Dont spoil view
Only put up when theres a flood forecast so theres a risk they may not be put up in time. Quite expensive
What are the advantage and disadvantages of flood plain retention?
Involves maintaining flood plain i.e. By not building on it
Helps slow floodwaters down and maintain flood plains ability to store water. No money has to be spent building flood defences
Restricts development and cant be used in areas
What are the advantage and disadvantages of river restoration?
Involves making river more natural eg. By removing man made levees so that flood plain cam flood naturally
Less risk downstream discharge is reduced. Little maintenance needed.
Can increase local flood risk, especially if nothing is done to prevent major flooding
