rivers Flashcards
whats a tributary
a stream or river that joins a larger river
whats a drainage basin
area of land drained by a river system
whats a watershed
line of seperation between 2 river systems
whats a confluence
the point where 2 rivers meet
whats a interception
precipitation thats collected and stored by vegitation
whats infiltration
movement of water into a soil, rate at which water enters soil depending on intensity of rainfall,permeability of the soil and extent of water saturated in soil.
whats a throughflow
downslope movement of water into soil
whats abrasion (corrasion)
the wearing away of river bed by the sediment carried througha river
whats attriciton
wearing away of sediment as 2 particles colide and hit eachother to become smaller and rounder particles
whats hydraulic action
the force of air and water on cracks and sides of a river
whats groundwater flow
underground movement of water from the land to river
whats suspension
small particles held up by flow in the river
whats saltation
heavier particles bouncing along the river bed
whats soloution
when sediment dissolved in water
whats traction
when sediment is dragged or rolled along the river bed
how does the hydrologocal cycle start
when precipitation or condensation occurs and water gets inflitrated through soil then leaves the system during dischararge,evaporation or transpiration
whats the source of a river
area where the river begins
whats the mouth of a river
the area where a river meets the sea
what happens in the uppercourse of a river (4 features)
-gradient is at its peak
-sediment shape is large
-slow average velocity
-mainly transporation of sediment
what happens in the middle course of a river (4 features)
-sediment is broken up and smoother
-gradient is less steep
-mainly erosion occurs
-wide cross section
what happens in the lowercourse of a river (4 features)
-flat gradient
-super small sediment
-mainly deposition (discharge of minerals)
-very fast average velocity
whatre the 3 features in the upstream of a river according to bradshaws model
-larger particles sizes
-channel bed is rough
-a steep gradient
whatre the 5 features in the upstream of a river according to bradshaws model
-increase in discharge
-wider channel width
-inc in channel depth (due to water pressure pushing channel down)
-inc in sediment quantitiy
-increase in average velocity due to wwater buildup
what does vertical erosion do
dominant in the upper course of rivers. It increases the depth of the river and valley, as the river erodes downwards
what does lateral erosion do
dominant in the middle and lower course of rivers. It increases the width of the river and valley as it erodes sideways
what are the 4 erosion processes
-Hydraulic action (water and air forces create cracks and damage river bed)
-Abrasion (sediment wears away river floors)
-Attrition (2 rocks colide and break eachother down)
-solution (sediment dissolves in water)
what 5 factors increase erosion
-heavier and sharper load
-greater velocity and discharge
-steeper gradient
-soft rocks (more easily eroded)
-water acidity (inc solution)
whatre the 4 processes of transporation
-Traction (larger rocks roll along river bed)
-Saltation (smaller material bounces along river bed)
-Suspension (lighter sediment carried by river flow)
-Solution (sediment dissolves)
why does deposition occur
due to a decline in energy or velocity
compare hydraulic action with abrasion
hydraulic action is the force of water and air on sides and cracks in rivers while abrasion is when large pieces of sediment erode the river bank
whatre the 4 landforms created by uppercourse rivers
Waterfalls
Gorges
V-shaped valleys
Interlocking spurs
what are the 2 main erosional processes in the formation of waterfalls
abbrasion and hydraulic action
describe how a waterfall forms
-The soft rock erodes quicker, undercutting the hard rock and creating a plunge pool
-This leads to the development of an overhang of hard rock which eventually over time, collapses
-the overhang falls into the plunge pool increasing abrasion and making the plunge pool deeper
-The process then begins again and the waterfall retreats upstream leaving a steep sided gorge
describe the formation of v shaped valleys
- Vertical erosion is dominant in the upper course of the river
-This cuts down into the river bed and deepens the river channel
-Weathering and mass movement leads to material from the valley sides collapsing into the river forming a steep v-shaped valley
describe the formation of interlocking spurs
-in the upper course of the river the channel starts to meander
-Erosion happens on the outside of the bend
-in the upland areas this forms interlocking spurs
what are the 4 landforms created by the lower course
Meanders
Ox-bow lakes
Floodplains
Levees
whats a floodplain
how do meanders form
-in lowland areas lateral erosion is dominant
-Meanders increase in size
-The fastest water flow (thalweg) is on the outside of the river bends, leading to erosion:
-The erosion undercuts the riverbank forming a river cliff
-The riverbank collapses and the edge of the meander moves further out
-The slowest flow is on the inside of the river bends, leading to deposition:
-the deposits form a slip-off slope
-Deposition on one side and erosion on the other leads to the meander migrating across the valley
how do oxbow lakes form
1- erosion and deposition form around ameander
2-increased erosion during floow conditions which exaggerates the meanders
3-river hreaks through during floods which causes firther depoisition which causes the meander to turn into an oxbow lake
explain how waterfalls and gorges are formed (4)
waterfalls occur on horizonally bedded rocks,soft rock is undercut by hydraulic action and abrasion to form a plunge pool. softer rock is eroded by fractions of the harder rock that break off,weight of water and lack of support causes the waterfall to collapse and retreat which forms a gorge
what is an impermeable rock
rock that does not allow liquid or gas to flow through it
what is lag time
The time taken for river levels to rise after a storm
when does flodding occur
When the amount of water exceeds the capacity of the river’s channel. The excess water overflows the river’s banks and spills out across the flood plain. It can occur as a result from persistent rain over a relatively long period of time.
what are the 6 physical causes of flooding
1) Weather - Intense rainfall greater than the infiltration capacity of the ground. Prolonged rainfall leading to the satiation of the ground. Rapid snow melt as temperatures suddenly rise about freezing.
2) Rock - Impermeable rocks limiting percolation and encouraging rapid surface run off.
3) Soil - Low infiltration rate in certain soils (clays)
4) Relief - steeps slopes causing fast run off
5) Drainage Density - High drainage density means many tributary systems can carry the rainwater quickly to the main river.
6) Vegetation - Low density vegetation absorbs little water
what are the 4 human causes of flooding
1) Deforestation - cutting down trees reduces interruption and speeds up run off.
2) Urbanisation - concrete and tarmac surfaces together with drains mean quicker delivery of rain water to the main river.
3) Agriculture - Risk of flooding increase by leaving soil bare.
4) Climate Change - Burning fossil fuels causes melting of ice sheets and glaciers as well as more rainfall and more frequent storms.
how can rivers be used as an advantage
-the silt deposited during flooding is often rich in minerals and nutrients, making it ideal for growing crops
-Rivers are a source of food
-The floodplains are flat land which makes the construction and building of transport networks easier
-Water can be used to irrigate farmland
-Leisure and tourism
-Generating electricity
-Transporting goods and people
whats a levee
A embankments on the sides of the river made from layers of sediment deposited from flooding.
what do dams do
-reduce speed of water flow,control amount of water in a river,cause deposition behind dams,increase erosion downstream of the dam,change ecosystems,increase pressure on rocks and maaybe cause earthquakes
how can we manage the impacts of flooding
-building dams to hold back excess water
-raising river banks
-create new flood relief channels
whatre the hazards of floods and river erosion
-Flood waters may increase the spread of water related diseases;
-Deaths and injuries as floodplains are often densely populated due to the fertile soils
-Bridges and transport routes may be damaged or destroyed by the flood waters
-erosion of the river banks leads to the loss of farmland, housing and transport routes
-Destruction of crops
-Increased insurance costs
-Lower house prices
Explain how a waterfall is formed on a river. You may use a labelled diagram or diagrams (5)
-Hard rock overlies softer rock / (passes over) hard then soft / alternating
hard and soft;
-Hard rock resists erosion / softer rock is eroded rapidly;
-Undercutting / overhang develops;
-Overhang collapses;
-Retreat of waterfall / process repeats;
-Specific named methods of erosion or description of it
For a named river you have studied, explain the causes of flooding.(7)
-Heavy rainfall,
-Rainfall over a long period of time,
-Impermeable rocks,
-Rocks reach saturation level,
-Snow / ice melt,
-Deforestation,
-Urban development
-Storm surges
-High spring tides
-Cyclones – so coastal flooding idea fine at estuary
-Lack of river management
