Component 2 - Rivers Flashcards
Describe the water cycle
- Water evaporates and condenses into clouds,
- This falls onto the land, where some of it re enters the atmosphere through evapotranspiration, some will go into rivers. The rest soaks through the soil through infiltration and will return to the sea.
- Some undergoes percolation and turns into groundwater, this will take 1000s of years to return to the sea.
What are the 3 courses of a river?
Upper, middle and lower.
Where is the upper course of a river found?
The upper course is found high up in mountains.
What are the features of the upper course?
- The river doesn’t flow fast and is small.
- River rolls stones across the river bed through traction
- The river gathers minerals from mountain rocks
- River flows in interlocking spurs
- Forms V-shaped valleys
- Waterfalls
What are the features of the middle course?
- Meanders
- River flows faster
- Carries soils and clays, as well as minerals from upper course.
- Cities found here
- Murky
Where is the middle course of a river found?
The middle course is found on wider, flatter and open plains.
Where is the lower course of a river found?
The lower course is found near the coast.
What are features of the lower course?
- Extremely wide and flat
- River is slow at high tide, fast at low tide
- Supports large shipping lanes
- Sediment and minerals deposited making soil very fertile
- Industry, farms and ports found here.
What are the 4 types of erosion found mostly in the upper course?
Abrasion, Attrition, Hydraulic action and solution
How do V shaped Valleys form?
1.The river cuts downward into the land, as stones are dragged along the river bed.
2.The sides of the valley are exposed and are eroded by weathering.
3.The weathered material falles via gravity, into the river where it is carried away. Creating a V shaped valley
How are waterfalls formed?
1.Begins on a downhill slope when a layer of soft rock sits beneath a layer of harder rock.
2.Overtime the soft rock erodes faster, creating a step in the river
3.The soft rock is eroded further, until a steep drop is created - a waterfall
How are gorges formed?
- The waterfall undercuts the hard rock, which creates an unsupported overhang
- The hard rock collapses and the waterfall recedes.
- The collapsed rocks swirl around at the foot of the waterfall, where they use abrasion to create a plunge pool.
- This creates a gorge, which gets bigger as the waterfall recedes.
How are Oxbow lakes formed?
- The river meanders so far it connects back up with itself.
- The river takes shortest path, and sediment is deposited blocking off the old meander
- Forming an oxbow lake.
What are the main types of flooding?
- Glacial outbursts
- Fluvial flooding
3.coastal flooding
4.Saturation flood
5.Sewer flood - Flash flood
7.Catastrophic floods
8.Liquefation floods.
How do glacial outbursts happen.
1.Volcano erupts, or there is increased activity beneath a glacier.
2. Melting of huge volumes of ice causes torrent of water.
How does Fluvial flooding happen?
- When a river bursts its banks due to the inflow being greater than the outflow.
- Caused by heavy rain
What is the most common type of flooding in the UK?
Fluvial flooding
What is fluvial flooding good for?
Creating fertile land
What is coastal flooding caused by?
1.Sea storms and rising sea levels cause low lying land to flood
2. Worsened by climate change
How do Saturation floods work?
- Days of moderate rainfall cause the soil to become saturated, so it floods
How does sewer flooding work?
1.Sewer drainage becomes overwhelmed
What is dangerous about sewer flooding?
It is a significant biohazard, contamination can take weeks to clean
Why is sewer flooding common in the UK
Sewers are old.
Why are flash floods dangerous
It happens suddenly and violently, it is more common in cities because there is nowhere for water to go.
Hard to predict
How does liquefaction flooding work?
After an earthquake, groundwater is pushed out of the ground by the vibrations. It is near instantaneous, however is rarely deep. Makes rescue harder though.
What is traction?
Material rolled along the riverbed during high flow
What is suspension?
Material floating in the water, making it murky
What is saltation?
Material bouncing along the riverbed
What is solution?
Dissolved material such as salts, invisibly carried in flow
How do you work out the base flow of a river?
Depth X width X velocity = base flow
What does base flow mean?
Normal rate of discharge of a river.
What is a hydrograph?
A type of graph used to show how the flow of a river changes over time.
What does cumecs stand for?
Cubic Metres Carried per Second
What are hydro dams?
Huge concrete structures that block rivers and produce electricity
What are raiseable barriers?
Huge structures that can be opened or closed to prevent water surging up or down a river.
What are wiers?
Small walls that slow a river down.
What is hard engineering?
The use of large structures to control natural processes
What is soft engineering?
The use of ecology and the natural environment to control natural processes.
What is vertical erosion, and where is it most common?
1.It deepens the river valley and channel, making it v shaped
2.It is dominant in the upper course
What are some reasons why a river would deposit material?
1.The volume of water in the river falls
2.The amount of eroded material in the water increases
3.The water is shallower
4.The river reaches its mouth
Why do rivers form interlocking spurs in the upper course?
1.The rivers aren’t powerful enough to erode laterally, so they wind around the hill side, creating interlocking spurs.
How are meanders formed?
1.The current is faster on the outside of the bend, because the river channel is deeper so there’s less friction
2.So more erosion occurs there, forming river cliffs, and bending the river outwards
3.The current is slower on the inside of the bend, as the river channel is shallower so there is more friction
4.This means eroded material is deposited here, forming slip off slopes and causing the river to bend further
What are levees and how are they formed?
1.natural embankments along the edges of a river channel
2.During a flood, material is deposited across the whole flood plain
3.The heiest material is deposited closest to the river channel, because it gets dropped first when the river slows down.
4.Overtime this builds up, creating levees.
how are deltas formed?
1.The rivers slow down when they meet the sea
2.This causes them to deposit material
3.This builds up and blocks the channel, forceing the river to split up into distributaries
4.This then becomes a delta.
What is peak discharge?
The highest discharge in the period of time you’re looking at
What is the rising/falling limb?
1.The increase/decrease in river discharge as rainwater flows into, or out the river.
What is the lag time?
The delay between peak rainfall and peak discharge
What physical factors affect hydrographs?
1.geology/soil type - water can’t infiltrate impermable rocks or soil, so the river fills faster
2.Slope - the steeper, the quicker the river fills
3.Previous weather conditions - if it was wet, the water will be saturated, making the river fill quicker
How can human factors affect hydrographs?
1.Water can’t infiltrate into impermeable surfaces like roads, so there’s more runoff
2.Drains quickly take water to rivers
3.Deforesting trees reduces the amount of water taken up by them, increasing runoff too
What are some soft engineering ways to manage flooding?
1.Flood plain retention
2.River restoration
What is flood plain retention?
1.Not building on the rivers flood plain, so that the river has somewhere to flood
What is river restoration?
1.Making the river more natural, so the flood plain can flood naturally
2.This means there is less risk of flooding downstream, as the discharge is reduced.
