river geography

attrition (erosion)

load carried by river bump into each other leading to them being smooth and broken down into smaller particles

solution/corrosion (erosion)

acids in water slowly dissolve the bed and banks

confluence

two rivers join together

saltation (transportation)

pebbles bounce along river bed commonly at source

suspension (transportation)

lighter sediment is suspended within water most commonly at mouth

solution (transportation)

dissolved chemicals is transported

how does the long profile change of the river?

height decreases rapidly from upper to lower course

how does cross profile in the upper course look?

low amounts of water so large amounts of vertical erosion so channel is shallow and narrow

how does cross profile in middle course look?

some vertical erosion but more lateral erosion so channel is wider and deeper as a result

how does cross profile in the lower coarse look?

lot less lateral erosion yet channel at its widest and deepest

Bradshaw Model characteristics

increases-discharge, channel width, channel depth, velocity,load quantity

decreases-load particle size, channel bed roughness, slope angle (gradient)

interlocking spurs (u)

land jutting out causing the river to meander, as the river flows downstream it winds and bends avoiding har rock and eroding soft rock leading to interlocking spurs (looks like a zip)
-steep gradient
-convex slopes
-narrow valley floor

watershed

edge of a drainage

source

start of a river

mouth

where river flows into the sea

tributary

a smaller river that joins into a larger river

hydraulic action (erosion)

1) water forces against bed and banks entering cracks causing them to widen

2) eventually beds and banks become weaker and break up

3) the material ends up in the river

abrasion (erosion)

the river throws the material in it against the bed and banks sometimes at high velocity causing a sandpaper effect

traction (transportation)

large, heavier pebbles are rolled on river bed

when is load deposited?

larger rocks-upper coarse
finer sediment-further downstream

v-shape valley (u)

1) river's volume and discharge is low and uses most of its energy to overcome friction with channel ,using hydraulic action to deepen channel (vertical erosion)

2) Upland area are hard rock (granite/slate) freeze thaw weathering broadens the valley forming v shape. Repeated weathering weakens hill rock fragments becoming loose and tumble downhill as scree which river removes

3) winding path of river as it takes the easiest route which is the soft rock and avoiding hard rock leading to interlocking spurs

rapids (u)

fast flowing turbulent white water sections of river which has steep gradient. formed by bands of hard rock and soft rock which erode at different differential rates leading to bed becoming uneven and water is turbulent

waterfall (u)

steep descent of river over a rocky cliff

1) water flow over a band of hard rock overlaying soft rock, due to differential erosion soft rock erodes first

2) overtime erosional processes such as hydraulic action and abrasion will erode soft rock below making a plunge pool

3) soft rock further erodes forming an undercut causing an overhang of hard rock, but as its unsupported it will collapse

4) process repeat continually resulting in waterfall to retreat upstream creating a steep sided gorge

gorge (u)

a narrow steep sided valley found downstream of a waterfall

1) as waterfall retreats upstream it leaves a gorge

2) every time a section of overhanging rock breaks the gorge grows

meander (m)

series of regular sinuous curves,bends,loops,turns or windings in river channel

1) forces of water erodes the outer bend using abrasion and hydraulic action as water flow has most energy due to the decreased friction as water is deeper causing a river cliff

2) inner bend doesn't have much energy so deposition occurs creating slip-off slopes or beach

3) overtime causes a horseshoe shape river, cutoff loop is called oxbow lake

oxbow lake (m)

1) meander loop becomes large and neck of meander narrows due to lateral erosion

2) only narrow land separates river

3) when river floors at high discharge the main flow of river cuts straight through neck

4) meander is abandoned as river continues on straight path

5) after flood velocity of water decreases

6) former meander left as horseshoe shaped oxbow lake cut off from main channel

7) marsh plants colonise area further widening gap

8) eventually dry up to form meander scar

levees - characteristics (l)

-naturally raised river banks (2-8)
-made of gravel, sand, alluvium
-heaviest material closes to river
-flat tops so can be used as footpath

levees - formation (l)

1) during a flood, volume of water is spread across the large floodplain creating large surface area so lots of friction, therefore reducing velocity so losing energy so deposits

2) heavier, coarser sediment deposited closest to the river and finest particles of sediment carried further on flood plain

3) after every flood banks get higher as bed load deposited but also river bed builds up so increases flood risk

floodplain - characteristics (l)

-large flat area of land
-prone to flooding
-made up of alluvium (silty soil) which is excellent for farming as it makes soil fertile

floodplain (l)

flat land in lower course prone to flooding

esturary - characteristics (l)

-tidal part where freshwater meets salt water
-high tidal range
-mudflats visible at low tide
-may have tidal bore

mudflats (l)

1) formed in sheltered area where tidal water flows slowly

2) where sea and river meets, velocity is reduced leading to deposition

3) layers of sediment builds up forming mudflats

4) visible at low tide and may have small creaks (streams) running through

Physical factors affecting flood risk

Precipitation - torrential rainstorms and/or prolonged periods of rain can lead to flooding. (e.g. flash floods occur in summer and associated with heavy rainstorms)

Geology - impermeable rocks don't allow water to pass through, so it flows overland into river channels.

Relief - steep slopes mean water flows quickly into river channels.

Vegetation-reducing risk of flooding by increasing lag time therefore increasing infiltration

Human factors affecting flood risk

New infrastructure and disappearing gardens- precipitations can't infiltrate ground so surface run off straight to river so river overflows causing flood

New houses- houses built on Greenfield sites so greater amount of impermeable surface

deforestation- precipitation is no longer intercepted by vegetation

farming- downhill ploughing rather than contour ploughing can increase speed at which water gets to river on hill
- cattle compacting soil leading to ground becoming more impermeable

Hard engineering strategies for flood defences

-dam

-channel straightening

-embarkments

-floor relief channel

what is dam?

large concrete barrier built across a river to impede it’s flow causing a valley forming behind dam forming a reservoir

dam benefits

-boots tourism

-promotes new habitats

-source of drinking water

dam consequences

-displacement of people (area behind is flooded)

-expensive

-wildlife interruption (migrating fish)

channel straightening

meandering part of river is engineered to be wider, deeper and straighter course

channel straightening benefits

-reduces flood risk (moves water out the area and has fast flowing water so no build up of sediment)

-confident home owners

channel straightening consequence

-pushes problem downstream

-expensive but less than dams

-wildlife interruption

embarkment

artificially raises banks so river can hold more water

embarkment benefits

-cheap compared to other methods

-walking routes

-new habitats

embarkment consequence

-breached embarkments (water takes a long time getting back to river and lies on land for too long)

-maintenance

-recreation (deprive people of access to fishing and boating)

flood relief channel

artificially made channel that is designed as a backup channel for river that frequently floods

flood relief channel benefits

-recreation (for boating, footpaths, cycle routes)

-increased house prices

-habitats

flood relief channel consequence

-flood downstream as channels merge

-displacement of people

-expensive

soft engineering strategies for flood defences

-flood warning and preparation

-flood plain zoning

-afforestation

-river restoration

flood warning and preparation

warning issued by environmental agency through TV, radio and internet giving chance to protect homes and evacuate

flood warning and preparation benefits

-protection for valuables

-low costs so cheap

flood warning and preparation consequences

-only effective for those who listen and take action

-doesn’t avoid flood so still high insurance

-could be distressing

flood plain zoning

land next to river used as farmland or recreational use but buildings further away

flood plain zoning benefits

-reduce impermeable surface as building restriction on flood plains, so reducing flood risk

-low costs only administration

-leaves habitats near river

flood plain zoning consequence

-too late as cities have already been made on floodplains

-housing shortages

-habitats destroyed as buildings would be on Greenfield sites

afforestation

trees planted near river so higher interception of rainwater preventing soil from becoming saturated too quickly

afforestation benefits

-more co2 absorbed so less affect on global warming

-adds variety of biodiversity

- relatively cheap

afforestation consequence

-loss of potential grazing land

-unhappy farmers as trees will take nutrients from the soil

river restoration

river previously hard engineered allowed to go on it’s natural course

river restoration benefits

-adds biodiversity

-aesthetically pleasing ,boosting tourism

-increased water storage in flood prone area reducing flood risk

river restoration consequence

-loss of land (such as agricultural land)

-expensive like a million

-not always practical

why was Jubilee relief channel needed?

-contains Windsor which attracts many tourists

-very high properties in the area that need to be protected

-historic prestigious public school attended by MPS and royal families

Jubilee relief channel characteristics

-cost 330 million pounds funded by environmental agency

-opened 2002, 11.7km long, 50km wide

-UK’s largest artificial river

-designed to look natural with reef beds and meanders

-5 weirs/dams on course

Jubilee relief channel social issues

-3000 properties protected in affluent Windsor but less wealthy downstream suffers higher discharge

-much higher discharge as two channels merge

-paddle boaters promised navigable river but two weirs to carry boat around as too dangerous to cross

Jubilee relief channel economic issues

-most expensive flood relief scheme but after a year weirs damaged by floods

-EA ran short of funds to alleviate flooding downstream so businesses will have to make up 110 million pounds shortfall

-small business can’t contribute due to high insurance and if floods will have to close

Jubilee relief channel environmental issues

-algae collecting behind weirs disrupting natural environment

-concrete weirs ugly under normal flow conditions