rivers and coasts

-evaporation of water into atmosphere, wind moves it inland, condensation to form clouds and then precipitation falls

FLOWS:

• surface run off- overground
• groundwater flow- underground through rocks
• throughflow- underground through soil
• infiltration- seeping of water into soil
• percolation- vertically down through soil and rock

STORES:

• channel storage- river
• surface sotrage- puddles, lakes
• groundwater storage- underground in soil and rock
• interception storage- vegetation

-part of the hydroglogical cycle on land is in a drainage basin

drainage basin- area of land drained by a river, seperated by a watershed

same flows and storages

but inputs and outputs as well:

INPUTS:

• precipitation

OUTPUTS: 

• evaporation
• transpiration
• river flow into sea

WEATHERING- break down of rocks where they are by chemical, mechanical or biological processes

MECHANICAL: without changing chemical composition- freeze thaw weathering (continuation widens the cracks and causes rock to break up)

CHEMICAL- changes chemical composition- carbonation- co2 in rainwater reacts with rocks containing calcium carbonate 

BIOLOGICAL- living things- plant roots or animals burrowing

course- path of a river as it flows downhill

long profile- how gradient changes 

cross profile- cross section, so how size of valley and channel changes

HYDRAULIC ACTION- force of water breaking rock particles away from channel

CORRASION- eroded particles scrape against channel and wear it away

ATTRITION- eroded particles banging into eachother and breaking into smaller fragments- rounded shape 

CORROSION- water dissolving some types of rock

transportation:

TRACTION- large boulders being pushed

SALTATION- pebble sizes particles bouncing along bed

SUSPENSION- small particles carried around 

SOLUTION- soluble materials dissolved and being carried along

deposition happens when river doesnt have enough energy to transport material any more

• velocity falls
• volume of water falls
• amount of eroded material increases
• shallower water- more friction
• mouth 

WATERFALLS:- form where a river flows over alternating layers of hard and soft rock

1. softer rock erodes quicker- step in river

2. continued erosion by hydraulic action and corrasion creates a steep drop 

3. hard rock is undercut by erosion- overhang becomes unstable and collapses- waterfall formed

4. collapsed rock forms a plunge pool and continuation of retreat forms a gorge 

V-SHAPED VALLEY- vertical erosion and mass movement 

INTERLOCKING SPURS- rivers arent powerful enough to erode laterally so have to wind around hillsides

MEANDERS- bend in a river formed because an obstruction in the path of a river causes it to bend

1. at a bend in the middle/lower course of a river- water flows faster on outside of bend because deeper so less friction.- more erosion forming river cliff 

2. water flows slower on inside of bend as shallower water so more friction- slip off slope

3. continued erosion of neck of meander causes river to break through, so river takes quickest route (straight)

4. deposition cuts off meander- OX BOW LAKE 

FLOODPLAIN- low-lying flat land that surrounds the edges of a river in its lower course and gets covered when the river floods

LEVEES- natural embankments formed when a river floods onto a floodplain and deposits its heaviest material first- closest to river, which builds up

DELTA- when material deposited at the mouth of a river builds up so much, low lying areas of land are formed and the deposition blocks the channel, causing the river to split into many distributaries 

• arcuate- rounded, many distributaries- NILE
• cuspate- triangular and few distributaries- TIBER
• birds food- MISSISSIPPI

rising limb, falling limb, peak discharge, lag time 

things that increase steepness:

• impermeable surfaces
• impermeable rock
• high rainfall
• saturated soil 
• steep slopes
• less vegetation

urban areas have drainage systems which increase discharge and more impermeable surfaces

PHYSICAL CAUSES OF FLOODING

• prolonged rainfall- saturated soil
• heavy rainfall- lots of water at once
• snow melt- lots of water at once
• relief (gradient of land)- faster run off
• geology- less percolation

HUMAN CAUSES:

• deforestation- less interception and soil erosion raises bed 
• urbanisation- impermeable surfaces

impacts of flooding:

• houses lost
• businesses destroyed
• schools shut
• no elec
• polluted water- disease
• deaths
• jobs lost

worse in LEDC's as:

• less money to spend on flood defences, l
• ess money to help people afterwards,
• farms are more easily destroyed and more people depend on farming,
• poor transport links- harder to get to people

HARD ENGINEERING- man made structures to try and reduce chances of flooding

• dams and reservoirs- store water and control flow
• channel straightening- get water out of area quicker
• man made levees- river channel can hold more water

SOFT ENGINEERING: schemes set up to reduce impacts

• flood plain zoning- restrictions preventing houses being built on floodplain so less damage
• flood warnings- people have time to prepare
• preparation- modify homes and businesses, make a survival kit etc to reduce impacts

weathering processes are the same 

erosion processes:

HYDRAULIC ACTION- when waves crash into cliffs, they compress air into crack which puts presure on them and causes them to expand and rock to break off

corrasion and attrition the same

CORROSION- weak carbonic acid in sea water dissolves some rock

DESTRUCTIVE WAVES: waves that erode coastlines 

• backwash > swash
• steep
• high frequency 
• formed by strong winds and large fetch (distance of water wind has blown over to form wave)

CLIFF RETREAT:

1. waves crash into foot of cliff- erosion- wave cut notch 

2. cliff above notch is unstable due to erosion and weathering- it collapses (mass movement)

3. collapsed material washed away and process starts again

4. continuation forms a wave cut platform and cliff retreats 

rate depends on geology of rock and whether its covered in vegetation (more veg= more stable)

types of MM:

• slide- straight line 
• slump- rotation
• rock fall- vertical

HEADLANDS AND BAYS:

formed where there are perpendicular alternating bands of hard and softer rock along a coast

1. less resistant rock eroded quicker forming a bay- gentle slope

2. resistant rock sticks out as headlands either side- steep sides

COVES:

formed where there are parallel bands of hard rock with soft rock behind it on a coast

1. weaknesses in outer band of hard rock- creates narrow gap

2. softer rock behind it is then exposed and it erodes much quicker to form a cove- a wide circular bay with a narrow entrance

CAVES, ARCHES, STACKS AND STUMPS:

1. crack in headland expand by hydraulic action and corrasion, forms a cave

2. continued erosion deepends the cave until it breaks through the other side- forming an arch

3. rock supporting the arch becomes unstable and collapses

4. one side of the arch is seperated from rest of headland in the sea- stack

5. erosion of top of stack wears it down to form a stump 

LONGSHORE DRIFT- transportation of material along a coast by waves

1. waves hit the coast at an oblique angle, swash carries material up the beach in same direction

2. backwash carries material back down the beach at 90 degrees- material zigzags along coast

coasts are built up when deposition is greater than erosion. 

the amount of material deposited on the coast increases when:

• theres more erosion elsewhere
• more transportation brings more material into the area

constructive waves are waves that build up coastlines by depositing material:

• swash > backwash
• low and long 
• low frequency 
• formed by weaker winds and shorter fetches

BEACHES: found on coasts between high water mark and low water mark 

formed by constructive waves

SAND: flat and wide, gentle slope- as smaller particles so weaker backwash can move them back down the coast 

SHINGLE: steep and narrow- weaker backwash cant move bigger particles down the beach

SPIT- formed when there is a sharp bend in the coastline- LSD continues to transport material beyond bend and deposit it in the middle of the sea. strong winds and waves cause a recurved end 

area behind recurved end is sheltered so can form salt marsh

BAR- when the spit joins 2 headlands together. a lagoon is formed behind 

ECONOMIC REASONS TO PROTECT COASTS:

• loss of tourism
• businesses destroyed
• property pries fall
• house insurance increases
• farmland destroyed as salt reduces soil fertility 

SOCIAL:

• deaths 
• homelessness
• unemployment 
• water supplies damaged
• infrastucture damaged

ENVIRO:

• nature reserves destroyed and salt can kill animals 

HARD ENGINEERING- man made structures to reduce flooding and erosion

• sea wall- reflect waves back to sea to reduce erosion + physical barrier for flooding
• groynes- prevent LSD to create wider beaches which slow the waves- reduce erosion 
• rip rap- absorb wave energy
• revetments- deflect waves back to sea to prevent erosion 
• gabions- absorb wave energy
• breakwaters- blocks boulders offshore- make waves break further out so they lose their power

SOFT ENGINEERING- schemes to reduce effects 

• managed retreat- allowing land to flood- creates marshland and reduces flooding behind
• beach replenishment- pumping sediment to create wider beaches to slow waves