Topic 4 - River Processes And Pressures (set B)✔️ Flashcards
Define a flood plain?explain how they ‘build’ up?
Wide valley floor on either side of a river which occasionally gets flooded - when a river floods onto the flood plain, the water slows down and deposists the eroded material that its transporting which builds up the flood plain
Explain how meanders effect flood plains?
Meanders migrate across the flood plain making it wider - meanders also migrate downstream, flattening out the valley floor - deposition of meanders on slip-off slopes also builds up the flood plain
What are levees?
Natural embankments along the edges of a river channel - built up from eroded material being deposited over the whole flood plain during a flood - the heaviest material is deposited closest to the river channel
What are deltas?
Low lying areas where a river meets a sea or a lake caused when the river slows down and deposits the material its carrying which if not washed away builds up over time
How are distributaries formed?
When material is deposited as a river meets a sea a low-lying area of land (delta) is formed and because the sea doen’t wash it away the channel gets blocked so it is forced to split up into smaller rivers
Effect of a wetter climate on a river
wetter climates have higher discharge because there is more water which will increase the rate of erosion and transportation (because the river has more power as it has a higher volume of water) - also shapes the landscape forming v-shaped valleys and a wide , flat flood plain
How does freeze-thaw increase rivers seidment load?
Weathering increases the rivers sediment load and can make rockfalls more likley through freeze-thaw weathering
How does geology effect rivers?refer to sediment load and type of valley?
- rivers flowing through areas of hard rock have a slower rate of erosion so the river will have a lower sediment load - landscape will have gentler valley sides
- areas with softer rocks will experience more erosion resulting in increased sediment load - landscape is more likley to have steeper valley sides
How does slope processes effect rivers?
vertical erosion by rivers makes valley sides steeper, increasing the movment of material down the slopes - mass movement eg slumping can add large amounts of material to a rivers load
What is soil creep whats its effect on rivers?
Soil creep - when particles move down a slope because of gravity caused by the expansion and contraction of the soil (water adds weight to the soil and makes it expand which causes it to move down the slope) - soil creep adds lots of fine material to the river
What is river discharge?what is its unit?how is it represented?
The volume of water that flows in a river per second and is measured in cumecs (m^3/s) and shown on storm hydrographs
Explain 4 of the main points on a storm hydrograph?
- peak discharge - highest discharge in that period of time
- lag time - delay between peak rainfall and peak discharge
- rising limb - the increase in river disharge as rainwater flows into the river
- falling limb - the decrease in river discharge as the river returns to its normal levels
4 things which affect storm hydrographs?
- urbanisation
- deforestation
-geology
-soil type
How does urbanisation effect storm hydrographs?
Water can’t infiltrate into impermeable surfaces so theres more runoff - gutters and drains quickly take water into rivers
How does deforesation effect storm hydrographs?
Trees take up water from the ground and store it which reduces runoff - however when they are cut down they no longer can do that so this increases runoff and causes more water to enter the river channel
How does geology and soil type effect storm hydrographs?
Water cant infiltrate impermeable rocks of impermeable soil (eg clays) and shallower soils become saturated more quickly which results in more runoff
Human factors which result in the river Eden being prone to flooding?
- urbanisation and removal of soil/vegetation means less water is stored or infiltrates the soil so there is more water runoff into rivers
-removal of natural woodland and heathland - addition of drainage ditches means water flows rapidly to river channels
Physical factors which result in the river Eden being prone to flooding
- mild and wet climate - so there is more rainfall, therefore the river as a higher disharge
- has areas of hard, impermeable rock which doesn’t allow the water to soak into the ground
- snowfall is common on higher ground which can melt and add more water to the river channel, in a short period of time
Why is flooding increasing in the UK?
- increased frequency of storms and more periods of wet weather leaves the soil saturated and increases chance of flooding
- greater urbanisation as population grows and there is more expansion over flood plains and increased removal of vergetation and trees
How can flooding effect the enviorment?
- floodwater contaminated with sewage and rubbish can pollute river, damaging wildlife
- farmland can be ruined by silt and sediment deposited after a flood
- river banks are eroded which causes huge changes to the river landscape - trees/plants can be uprooted
How can flooding affect people?
- loss of possesions - damage to houses which can result in poeple made homeless
- buisness may be forced to shut down - can lead to loss of livelihoods
- people can be injured or killed
How do flood walls help prevent flooding?features?
Hard engineering - use of artificial barriers built along river banks to allow the river to hold more water - very expensive and not to attractive
How do embankments help prevent flooding?features?
Hard engineering - high banks that are built along or near the river banks which stop the rver flowing into built up areas during a flood, proetcting infrasturcture and buildings - can be buit with natural materials but are expensive and there’s a risk of severe flooding if the water rises above the level of the embankment
How do flood barriers (floodgates) help prevent flooding?features?
Hard engineering - built on river estuaries to stop flooding from storm surges or very high tides - they can protect large areas of land but are very expensive
How do flood barriers (demountable) help prevent flooding?features?
Hard engineering - provide temporary protection against flooding and are only put up when there’s a flood forecast so there is a risk they might not be put up in time and they are expensive however they dont spoil the look of locations
How does flood plain retention help prevent flooding?features?
Soft engneering - involves maintaining the river’s flood plain (ie by not building on it) so that the floodplain can flood naturally, so there is less risk of flooding downstream because discharge is reduced - requires little maintainace however can increase local flood risk
How does river restoration help prevent flooding?features?
Soft engineering - involves making the river more natural so that the river can flood naturally and there is less chance of it flooding downstream becauase discharge is reduced - very little maintance required - but can increase local flood risk
What is some evidence for the upper course of a river on a map?
- waterfalls are often marked on maps - close contour lines can also be evidence
- if the river crosses lots of contour lines in a short distance it indicates its steep
- if contour lines are very close together it indicates the valley floor is narrow and the river is in a steep-sided v shaped valley
What is some evidence for the lower course of a river on a map?
- river meanders across a large flat area (no contours) which is the flood plain
- the river’s wide
- river doesn’t cross any contour lines so its very gentle sloping
