Geography > Rivers > Flashcards
Rivers Flashcards
Precipitation
any source of mositure reaching the ground (rain and snow)
Strorage
Water held on the ground surface
Infiltration
water sinking into the soil/rock from the ground surface .
Percolation
water seeping deeper below the surface .
Groundwater
Water strored in the rock .
-water flowing through the soil layer parralel to the surface .
Transpiration
Water lost through pores in vegetation
evaporation
water lso from ground/vegetation surface .
run-off
water flowing on top of the ground .
interception
water being prevented fromr eaching the surfae by tree orgrass .
throughflow
water flowing though the soil layer parralel to the surface .
water table
current upper level iof sturated rock . soil where no more water is absorbed .
water shed
boundary of the drainage basim
confluence
where two rivers mee
channel
dip where the river flows .
tributary
small river which flows into the main river
meander
the bend of a river
source
the point where the river begins
How does a river erode
fluvial procesesses
hdyraulic action
attrition
abrasion
solution
hydraulic action
sheer force of fast-floowing eater hits the river anks and river beds and forces water into the cracks compressig air into crkcs , repeaed changes in air pressure weaken channel .
repsonsible for verticla eriosion in upper course
ltaeral in banks ,
abrasion
small boulders ad stones may scracth their ay down a iver wearing down river banks and beds .
journe a river amkes to sea is logn profile
jagged , n stuff also . ongoingabrasion responsible for verticla and lateral erosion of the channel .
attiriton
when stoens frrst eneter river jagged and angular , transprted downstream , stones collide iwth eachother as wella s river hbank and bed , and the jaged edges become more smooth and roundeds.
what is vertical erison
deepenign or river bed mosly by hydaulic action evient inupper coure ittle energyt he river ha left over overcomign friciton used to deepn channel .
lateral erison
Sideways erosion , wears away the bank of the river . Most evident in the lower course of the river .
wha is erosion
tranpsortation
depostion
the wearing away and removal of sedminet from the chnnael due to flwoing water
transportation
the way the sediment is moved b y the flowing water , sedimen carried withitnn the water is called LOAD
depostion is the sdiment dropped by the flwing water .
check book for river transport porcesses.
-Solution minerals are dissolved in the water , this affects soft rocks such as limesone and chalk . Load transported in this way is called solute load .
Suspension - fine light material is held up and carried wihin the rivers flow . This is called suspended load .
Saltation - small pebbles and stones are bounc The load is alternately lifed then dropped in line with a local rise and fall in the velocity of the water
Traction - large boulders and rocks re rolled along the river bed . Load carried in this way is called bedload.
upper course
msotly has vertical eriosion by hydruaic action
tration large boulders
depostied large boudlers
hih relief steep gradeint waterfaal rapid .
middle cours e
less verical eriosin more lateral eriosn atrition abrasion and solution
load trapsorited by suspension as laod is smaller
depostioed on meanders
hilly mounynioud . fidvhstgr invtrsdrf .
low course
evry little erisoin onl lateral eriosn
mostly suspensiona nd solutoin
sml particles of load . depositon now fluvial fin mterial deopstied
closes to rer mouth eriosn now confiend to lateral eriosn in meanders , flat gradient .
dischrge i he volume of water pasing thoruh a given point on the river .
waterfalla nd gorge
A waterfall is a sudden drop along the river course. It forms when there are horizontal bands of resistant rock (hard rock) positioned over exposed, less resistant rock (soft rock).
The soft rock is eroded quicker than the hard rock and this creates a step.
As erosion continues, the hard rock is undercut forming an overhang.
Abrasion and hydraulic action erode to create a plunge pool.
Over time this gets bigger, increasing the size of the overhang until the hard rock is no longer supported and it collapses.
This process continues and the waterfall retreats upstream.
A steep-sided valley is left where the waterfall once was. This is called a gorge.
interlocking spours
In the upper course there is more vertical erosion. The river cuts down into the valley. If there are areas of hard rock which are harder to erode, the river will bend around it. This creates interlocking spurs of land which link together like the teeth of a zip
oxbow lake
Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time.
Erosion narrows the neck of the land within the meander and as the process continues, the meanders move closer together.
When there is a very high discharge (usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route.
Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.
flood plain
A floodplain is an area of land which is covered in water when a river bursts its banks.
Floodplains form due to both erosion and deposition. Erosion removes any interlocking spurs, creating a wide, flat area on either side of the river. During a flood, material being carried by the river is deposited (as the river loses its speed and energy to transport material). Over time, the height of the floodplain increases as material is deposited on either side of the river.
leveee
Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.
Sediment that has been eroded further upstream is transported downstream.
When the river floods, the sediment spreads out across the floodplain.
When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away.
After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water (a greater discharge) and flooding is less likely to occur in the future.
estuary
An estuary is where the river meets the sea. The river here is tidal and when the sea retreats the volume of the water in the estuary is reduced. When there is less water, the river deposits silt to form mudflats which are an important habitat for wildlife.
rapids
Rapids are areas of shallow, fast-flowing water in a stream.
when the water goes from one hard rock that resists the water’s erosion to a softer rock that is easier eroded
check book for phycsical and human causes of flooding
.ri
hard engineering strategies
damns and rrsevoir
involves building artificial structures which try to control rivers
The dam traps water, which builds up behind it, forming a reservoir. Water can be released in a controlled way.
adv-Can be used to produce electricity by passing the water through a turbine within the dam.
Reservoirs can attract tourist
disadv-Very expensive.
Dams trap sediment which means the reservoir can hold less water.
Habitats are flooded often leading to rotting vegetation. This releases methane which is a greenhouse gas.
hard egnineering strategies
striaghtenrng
Straightening the river speeds up the water so high volumes of water can pass through an area quickly. Dredging makes the river deeper so it can hold more water.
Advantages
More water can be held in the channel.
It can be used to reduce flood risk in built-up areas.
Disadvantages
Dredging needs to be done frequently.
Speeding up the river increases flood risk downstream.
soft engineering
does not involve building artificial structures, but takes a more sustainable and natural approach to managing the potential for river flooding.
floodwarnigns and preparations - montioring so people can be preapred using sellites nd tv.
People have time to protect their properties, eg with sandbags.
Many possessions can be saved, resulting in fewer insurance claims.
Disadvantages
Some people may not be able to access the warnings.
Flash floods may happen too quickly for a warning to be effective.
They do not stop la
flood plin zoinign
Allowing only certain land uses on the floodplain reduces the risk of flooding to houses and important buildings.
More expensive buildings and land uses are further away from the river, so have a reduced flood risk.
Less damage is caused, leading to fewer insurance claims.
Disadvantages
Not always possible to change existing land uses.
Planners have to decide what type of flood to plan fo
how is relief a cuase of flooding ?
Physical cause
a stepepr releif means that therei s more runoff into the river compared to a flttr rellief which is wider so slower runoff .
How is rock type a cause of floodign ?
More impermeable rock causes more runoff s water cannot be absorred ,
-Compred t permeable rock as mroe water is absored so less run off .
How is soil a cuase of floodign ?
More saturated soi as thin layer of soil less through flow l , means more runoff les water is being absorbed .
Thick layer of soil means more though fow .
How is natural vegetation a cuase of flooding ?
vegetation mena sinterceptoopom od wayer as water is abroebd by the roots of th eplant os less run off .
Not a lot of vegetation , nothing can intercept the water so mroe run off
How is land use a cause of flooding ?
Urbanisaition like (tarmax) increases the impermebale layer .
Compared to rural areas , llittle armaxc more tree crop sin farming , so omre interception of wayer in increased irrigation .
How is land use a cause of flooding ?
Limitied use of river so all the water stays in the channne .
-Wter used for industry , dams built water either extracted frp river or flow is restricted .
How is draianage density a cuase of flooding ?
Higher density - mroe streams and tirbutaries to collect eater from land to chaneel into rivver .
Lower denisu fewer streams to collect water or more the for water to be increased or infilitrated , slowign journery into channel .
