topic 4 : the UK's evolving physical landscape

storm hydrographs

storm hydrographs

to measure a river's flow and show the change in river discharge over a short period of time after a storm

hydrograph

record of river discharge over a period of time

river discharge

cross sectional area x river mean (average) velocity

discharge

the amount of water in a river at any given point and time

what is discharge measured in?

cumecs (cubic metres per second)

velocity

speed of a river

what is velocity measured in?

m/s

lag time

the time taken between peak rainfall and peak discharge

rising limb

shows the increase in discharge on a hydrograph

falling limb

shows the return of discharge to normal / base flow on a hydrograph

peak rainfall

maximum rainfall (mm)

peak discharge

maximum discharge (cumecs)

base flow

normal discharge or flow of the river

list five factors influence the storm hydrograph

vegetation, urbanisation, intensity and duration of rain, saturated soil, climate, drainage basin size

why would vegetation influence the storm hydrograph?

influences the amount of rain intercepted more vegetation means more interception, so it takes longer/less water reaching the ground and therefore the river

why would urbanisation influence the storm hydrograph?

more impermeable surfaces so therefore there is no infiltration to rapid run-off which means the peak flow is achieved quickly

why would the intensity and duration of rain influence the storm hydrograph?

in a downpour the ground isn't able to abosorb the water quickly enough therefore the water reaches the river quickly

why would saturated soil influence the storm hydrograph?

this has absorbed as much water as it can therefore anymore water will run-off, reaching the water quickly

why would the climate influence the storm hydrograph?

extremes in weather e.g in winter the ground will freeze, so the water cannot infiltrate the ground causing rapid run-off

why would the drainage basin size influence the storm hydrograph?

if it's a large area it will have more land to drain and therefore more water

storm hydrograph

evaporation

the transfer and change of water from the ground into water vapour in the air

evapo-transpiration

the transfer and change of water from plants into water vapour in the air

condensation

water vapour in the air changing back into a liquid

how are clouds formed through condensation?

it forms small droplets which are visible as cloud

precipitation

the transfer of water from the air to the land. water can fall as snow, rain, or sleet

overland flow (surface run-off)

the transfer of water back to the sea over the ground surface

groundwater flow

the transfer of water through the ground back to the sea

perlocation

water seeping deeper below the surface into the ground layer

interception

water being prevented from reaching the surface by trees or grass

the water cycle diagram

explain how surface run off could be impacted by human actions (4 marks)

key points:

-human actions can speed up surface run-off

-buildings roads because roads can be large, flat and impermeable

-human actions slows down surface run-off

-planting more trees because trees can intercept rainfall preventing it from reaching the ground

drainage basin

an area of land drained by a river and its tributaries

what is the source in a drainage basin?

the starting point of the river

tributaries

the streams and smaller rivers that feed into a main river

most rivers flow down towards sea level even if they don't reach the sea. true or false?

false. the correction should be "all rivers flow down towards sea level

confluence

the point where two rivers join

watershed

an imaginary line that seperates one drainage basin from the next

flood plain

the area of low-lying ground that gets flooded when the river overflows

the river gets ________ as you go from the source to the mouth.

wider

surface storage

where water is held on the ground surface e.g. lakes, puddles

infiltration

where water sinks into the soil or rock from the ground surface

water table

the current upper level of saturated rock/soil where no more water can be absorbed

throughflow

water flowing through the soil layer parallel to the surface

groundwater

water stored in rock

when did tewkesbury flood?

july 2007

where is tewkesbury located?

tewkesbury is in the south-west of england, in the county of gloucestershire.

it’s in between the cities of bristol and birmingham, near the border of wales.

social impacts

• 13 people died and hundreds have to be evacuated

• 30000 properties without power for 48 hours

• infrastructure severely affected - roads were cut off and badly damaged

• most properties were damaged in the area

economic impacts

• more than 18000 insurance claims

• 9000 businesses affected

• flooding cost local councils £140 million

• argiculture sector severely affected

environmental impacts

• soils became degraded due to contamination from roads and industrial sites

• soils became waterlogged, destroying plants and crops

human causes

• building on floodplains

• no flood defences in Tewkesbury

physical causes

• little sunshine meant evaporation rates were low

• the geographical location of Tewkesbury is vulnerable to flood events due to two rivers meeting in the town

• soils were already saturated due to the heavy rainfall occuring in the months leading up to the flooding

• the summer of 2007 in England and Wales was the wettest

short term responses

• evacuation of vulnerable people

• flood warnings were issued by the environment agency

• 920 requests were made to recover flooded items

• army personnel supply food to the cut-off town of Upton-on-Severn

long term responses

• additional funds to protect important public utility buildings such as electricity substations and water purification funds

• £800 million to be spent on flood defences

freeze thaw

when rainwater enters gaps in rocks and freezes, the ice puts pressure on the rock and causes it to break

acid rain

rain containing high amounts of chemical pollutants such as nitric and sulfuric acids, which when it falls can react with the minerals in the ground and cause dissolving and decay.

biological weathering

when the roots of plants grow into cracks of gaps and pushes the rock apart

soil creep

individual particles of soil move slowly down a slope due to gravity

slumping

when the bottom of a valley side is eroded, the slope becomes steeper and the material slides downwards

hydraulic action

sheer force of water hitting the river bed and banks, wearing them away

abrasion

material scraping or rubbing along the banks and bed of the river

solution

river water is slightly acidic so can dissolve some rocks and minerals

attrition

particles in the river bashing into each other, wearing each other down and becoming smaller and rounder

traction

stones rolling along the river bed

saltation

smaller particles bouncing along the river bed

suspension

the water flow carries silt and sand particles

erosion

the breaking away and removal of materials by a moving force e.g. river, wave, glacier

four types of erosion?

hydraulic action, abrasion, attrition & solution

weathering

the breakdown & decay of rock by natural processes acting on rocks, cliffs & valley sides

three types of weathering?

physical, chemical, biological

mass movement

the movement of material down a slope due to gravity

four types of mass movement?

falls, slumps/slides, creeps and flows

mudflow

saturated soil flows down a slope

landslide

large blocks of rock slide downhill

rockfall

bits of rock fall off the cliff face, usually due to freeze-thaw weathering

transportation

the carrying of sediment downstream from the point where it has been eroded to where it is deposited

four types of transportation?

solution, suspension, saltation, traction

deposition

when a river loses energy it drops/deposits the sediment it has been carrying

freeze-thaw weathering

1. water enters cracks in the rock.

2. when air temperature drops below freezing, the water will freeze and expand by 9-10 percent putting pressure on the rock

3. the ice will melt and contract when the temperature rises above freezing

what happens if the process of freeze thaw weathering is repeated?

the rock will weaken and eventually shatter into angular fragments - the fragments may then be deposited as scree at the foot of a slope

onion skin weathering/exfoliation

when a rock's outer layer peels off due to extreme variations in temperatures

describe what happens with different temperatures in exfoliation

when temperature is high, the rocks expand e.g in desert areas, when temperature drops during the night, the rocks contract

describe how river processes of erosion, transportation and deposition change downstream (8 marks)

"You need to start at the upper course, then talk about the middle and lower course. Don't forgot to mention deposition. You must use correct terms."

what is the upper course like?

• narrow/shallow channel

• high bedload

• steep/v-shaped valley

what is the middle course like?

• open/gentle sloping valley with floodplain

• wider/deeper channel

• more suspended sediment

what is the lower course like?

• open/gentle sloping valley with floodplain

• flat and wide floodplain

• very wide and deep channel

upper course features

• interlocking spurs

• gorges

• waterfalls

• ‘v’ shaped valleys

middle course features

• meanders

• river cliffs

• slip off slopes

lower course features

• ox-bow lakes

• floodplains

• levees

why certain fluvial processes occur at different places along the river?

modal answer:
deposition processes occur in the lower course, e.g by the mouth of the river, this is because the river is moving slowly and will lose energy, causing it to drop sediment.

secondly, vertical erosion ocurs mainly in the upper course, e.g by a waterfall, this is because the water is travelling down a steep gradient and therefore erode downwards.

why is flood risk increasing in the UK?

• increasing population so more housing being built on floodplains

• changes to land use e.g more impermeable surfaces so greater surface run-off

• changes to weather patterns due to climate change e.g storms, drought

dams and reservoirs - hard or soft?

hard engineering

river straightening and dredging - hard or soft?

hard engineering

embankments (levees) - hard or soft?

hard engineering

flood relief channels - hard or soft?

soft engineering

demountable flood banters - hard or soft?

soft engineering

flood barriers/storm surge barriers - hard or soft?

hard engineering

flood warnings and preparation - hard or soft?

soft engineering

floodplain zoning - hard or soft?

soft engineering

river restoration - hard or soft?

soft engineering