Topic 4-Rivers Flashcards
What is river course
The path of rivers as it flows downhill
What us upper,middle andlower course
Upper course is closest to source of the river and lower,middle course is closest to mouth of river
What is river valley
Changes along river depending on erosion or deposition is having most impact
What is long and cross profile
Long profile-shows you how gradient steepness changes over different courses
Cross profile-shows you what a cross sevtion of river looks like
What is dischare
The volume of water flowing in a river measured in m3/sec or cumes
Upper,middle and lower course of river differences
Upper-steep-v-shaped valleys,steep sides narrow,shallow channel,more sediment,less dicharge,less velocity.more erosion from traction and saltation
Middle course-medium-gently sloping valley sides wider,deeper channel,more discharge,meanders,more velocity
Lower course-gentle-more velocity and discharge,very wide,almost flat valley,deep channel
Vertical and lateral erosion
Vertical erosion-this deepens the river valley and channel making it v-shaped. Its dominant in upper course of river. Hight turbulence causes the rough,angular particles to be scraped along river bed, causing intense downwards erosion
Lateral erosion-widens river valley and channel during formation of meanders. Dominant in middle and lower course
What is freeze-that weathering
Water gets into cracks and then freezes when temeprature goes below 0 degrees.
When water freezes it exoands which puts rock under pressure. Whe water thaws it contracts which releeases pressure on rock
Repeated freezing and thawing widens crack and causes rock to break up
4 processes of erosion
Hydraulic action-the force of water breaks rock particles away from river channel
Abrasion-eroded particles picked up by river scrape and rub against channel wearing it away.
Attrition-eroded particles smash into each other and break into smaller fragments. Edges get rounded off as rub together.
Solution-river water dissolves some types of rocks e.g chalk and limestone
Transportation-traction,saltation,suspension,solution
Traction-large particles like boulders are pushed along river bed by the force of water.
Saltation-pebble-sized particles bouncing along river bed by force of water
Suspension-small particles like slit and clay are carried along by water
Solution-soluble materiaks dissolve in water and are carried along
Deposition in rivers
When river drops eroded material. Happens when river slows down and loses velocity.
Rivers slow down:
-voume of water in river falls
-amount of eroded material in water increases
-water is shallower
-river reaches mouth
Waterfall formation
-forms over an area of hard rock followed by area of sot rock
-aofter rock is eroded by hydraulic action and abrasion more than hard rock creating a step in river
-as water goes over step it erodes more and more of softer rock
-a steep drop is eventually created called waterfall
-the hard rock eventually is undercut by erosion. Becomes unsupported and collapses
-collapsed rock swirled around at foot of waterfall wher bed is eroded causing plunge pool
-more undercutting causes more collapses causing waterfall to retreat leaving a gorge behind
V-shaped valleys and interlocking spurs
-slow river discharge in upper course so can only erode vertically downwards.
-valley sides are slowly borken down by weathering
-weathered material is transported via gravity and rainfall towards channel which steepens valley sides
-steep-sided narrow valley shape created
-rivers wund way through upper course and move around areas of hard rock as can’t erode them which forms interlocking spurs
Middle course landformsxmeander formation
-when river epare un middle stage they begin to erode lateralky and form large bends called meanders
-the current is faster on the outside of the bend because channel is deeper so more erosion takes place on the banks creating a river cliff
-the current is slower on the inside of the bend because the river channel is shallower so eroded material is deposited on inside of the bend forming slip-off slopes
-over time the erosion and deposition continue changing the coursebof the river and moving it slowly down the valley
Oxbow lakes formation
-erosion causes the outside bend to get closer until there only a small bit of land left brtween the bends
-the river breaks through this land, usually during flood and river flows along shortest course
-deposition eventually cuts off meander forming an ox-bow lake
Floodplain formation
Floodplain is wide valley floor on either side of river which occasionally gets flooded
-in the lower course the main river process is lateral erosion and deposition.
-on outside of meander bend river erodes on outer bend and river migrates. Usually moves down stream and outwards.
-after time meander erodes into hills and creats wide and flat area next to river called floodplain.
When river floods water spreads onto floodplain
-river slows slower due to friction so adds sediment and makes floodplain very fertile
Levee formation
-when a river floods it will slow down due to friction and will deposit heaviest material first.
-shingle are first deposited then sands and silts
-over time deposition builds up creating levees kn edge of channel
Delat formation
When river reaches sea or ocean it loses velocity and deposits sediment
- if river deposits sediment faster than coastal processes erodes it, sediment builds up in layers and channel gets blocked which forces channel to split up into distributaries.
- eventually material built up so fast low-lying areas called deltas are formed
Factors affecting hydrographs
Geology-wtaer can’t infiltrate through impermeable rocks so more runoff
Soil type-more impermeable soils can’t absorb as much water as sandy soils, which increases run off. Shallower soils also become saturated more qucikly than deeper soils
Slope-steeper slope less infiltration and higher run off
Drainage basin type-circular drainage basins have shorter lag time and higher discharge than narrow basins because water reaches channel at same time. Narrower basin it takes longer
Antecedent conditions-wet or very cold weather can increase runoff because water can’t finfiltrate staurated or frozen soils
Urbanisation-water can infiltrate into impermeable surfaces so more runoff
Deforestation-trees take up water from ground and store it which reduces run off. Deforestation increases run off which increases discharge
Physical factors increasing flooding
Impermeable rock is common in area,mainly igenous in lake district and limestone in pennies.
Wet anteceden conditions
Mountainous areas of the uk sith mountains been almost 1k high
Human factors affecting flooding
Carlise Impermeable and was an issue with drainage. The drains weren’y big enough to hold all the rain and quickly blocked with strom debris
Reservours in lake district became ful, quickly and couldn’t hold anymore water
Embankments-description?advantage?disdavantge?
High banks built on or near riverbanks
Stop water spreading into areas where could cause problems
Flood water may go over them
Flood walls
Artificial flood barriers designed to raise hieght lf river banks to hold more water
Prevent water spreading where high impact
Expensive to build and may cause flooding downstream
Demountable flood barriers
A temporary structure that is only installed when needed
Put up when a flood is forecast,then take down afterwards
Can only be used in specific locations and there is a risk that defence is not installed
Flood barriers
Floodgates built near river mouth to prevent storm surge or spring tide from flooding area behind barrier
Can be closed when high tide or surge is forecast and can protect large areas
Construction costs are high and need regular maintenance
Flood plain-rentention
Stratgeies to maintain and restore the river orginial flood plain
Allowing rivers to flood helps slows down water and recover sediment processes
A change in farmland can be a disadvanatge
River restoration
Using a variety of strategies to restore river original course
Allows river to flod but slows them down.natural rivers more attractive and create natural habitats
Flood banks are often still needed and flood-pain retention,changes in land use may bring disadavnatges
