Rivers Flashcards
definition
bed
bottom of river channel
definition
bank
sides of river
each river has two banks
definition
wetted perimeter
length of the bed and the banks in contact with the river.
definition
channel
route course that a river flows. The flow of the river is often described as channel flow.
definition
thalweg
fastest part of river, always near middle as there is less friction
describe the river processes
Erosion: the process of wearing something away. The river erodes in four main ways; attrition, corrosion, corrasion and hydraulic action.
Transportation: The river can transport material when it has excess energy. The river transports in four main ways; traction, saltation, solution and suspension. Material carried by a river is know as load.
Deposition: When a river does not have enough energy, it will start putting down the load.
describe the 4 types of river erosion
Corrasion (abrasion): load crashing and rubbing into a rivers’ banks and bed causing pieces to break off.
Corrosion (solution): water dissolving load, bed and banks.
Hydraulic action: Water and air getting into cracks in a rivers banks and bed causing erosion through increased pressure.
Attrition: Load crashing into each other in a river.
describe the types of river transportation
Traction: large pieces of load rolling along a river bed.
Saltation: load bouncing a long a river bed.
Suspension: smaller pieces of load being carried in a rivers flow.
Solution: dissolved pieces of material being transported in a solution.
what is the Hydrological Cycle (also known as the water cycle)?
continuous movement of water through the land, oceans and atmosphere. The hydrological cycle is known as closed system because water cannot be added or lost.
difference between open/closed system
Open System: water can be added or lost. A drainage basin is known as open system because water can be added in the form of precipitation and lost in the form of evaporation and transpiration
Closed System: where water can not be added or lost. The hydrological cycle is known as a closed system because it includes all the water on our planet and no water can be added to it, or lost from it.
what is:
Porous
Non-porous
Porous: An object (or ground) that can hold water i.e. it has pores where water can be stored.
Non-porous: An object (or ground) that can not hold water i.e. it does not have any pores
equation for river discharge
velocoty x cross section area
= velocity (in cumers - cubic metres per second)
what is river discharge?
amount of water flowing in a river at certain point
how does a v-shaped valley form?
there is vertical erosion on a narrow channel
erosion caused by rain, wind, frost
gravity causes slope to slip downwards
debris left in channel
how do potholes form?
material rubbed/thrown across river bed and banks and it becomes worn away
currents within river may swirl the material around the same spot to form a hole, known as pothole
how do waterfalls form?
river flows over a layer of hard rock, then over soft rock
softer rock erodes faster, creating a step called a nick point
vertical erosion is created, making nick point deeper
water & stones will erode backwards underneath (undercutting) the hard rock
plunge pool created by hydraulic action
an overhang of hard rock is created
overhang eventually collapses and waterfall retreats
formation of a meander and Ox -bow lake
river is flowing in a gently curving path as it enters the middle course
it flows faster and water is deepest outside the river bend
erosion and deposition cause bends to get bigger & are now called meanders
erosion on the outside creates a river cliff
deposition inside the bend creates a slip-off slope , it is like a small beach
as the meander develops the neck of the meander gets very narrow
eventually the river will break through the neck and the channel will straighten
very little water will flow around the meander loop and deposition will take place, creates ox bow lake
the ox bow lake will eventually dry out and may fill up in wet conditions
the meander process will begin again
formation of a delta
all rivers eventually enter the sea
as it reaches the mouth, it will be carrying a lot of load
as it enters the sea the velocity reduces so it starts to deposit the load and it builds up so much the main channel might be blocked
the water forces through and creates distributaries (smaller rivers)
more material is deposited, making the delta bigger, creating moire distributaries
delta becomes more stablished and stronger and bigger
people start to form villages and farm on the fertile land
conditions for a delta to occur
shallow sea shelf no currents, no strong tides or waves slow flowing river large load sheltered coastlines
case study
flooding in ledc
ganges delta/river - bangladesh - bay of bengal
likely to flood:
over half of banglsdesh lies below 6m above sea level, water can spread easily
monsoon climate, lots of rain in short period
heavy rain at same time as highest temp. ice on himalayas melts and adds to discharge of the river
global warming
human mismanagment: building on flood plains, deforestation
problems: transport links swept away no electricity for several weeks full hospitals, diseases (cholera, diarrhoea) no safe drinking water
how do waves form?
they are formed by the transfer of energy from the wind over the surface of the sea. It breaks because the top of the wave moves faster and the bottom is slower because of friction and the top eventually falls & wave begins to break
4 processes by which waves erode land
Corrasion (abrasion): load crashing and rubbing into a cliff
Corrosion (solution): salts & acid dissolve a cliff.
Hydraulic action: Water and air getting into cracks in a cliff.
Attrition: Load crashing into each other in beach.
formation of
headlands, caves, sea arches, stacks, and stumps
(landforms created by erosion)
coastline made up of different bands of hard rock and soft rock
soft rock will erode more quickly, creating bays
hard rock will stick out creating headlands
waves will hit headlands. Hydraulic action will erode more of any weaknesses in the rock, eventually creating a cave
the cave will eventually expand through the headland creating a sea arch
as the arch gets bigger gravity will cause the top to collapse, creating a stack
the stack will be worn away, creating a stump
this process will repeat leaving a series of arches stacks and stumps
formation of
cliffs and wave cut platforms
(landforms created by erosion)
a cliff will erode between the low tide mark and the high tide mark, the undercutting will increase, creating a a wave cut notch
the top eventually falls and the cliff retreats
formation of a spit
landforms created by deposition
prevailing wind is the direction the wind normally blows, waves hit the coast in that direction
longshore drift moves in the direction of prevailing winds, that also moves sand and stones
as the direction of the coast changes but winds stay the same direction, material will build up to form a beach that stretches out into sea, this is called a spit
the end of the spit often becomes hooked due to storms from the opposite direction
a salt marsh may develop behind the spit where there is less energy
grass may grow making the spit stronger and more permanent
what causes rivers to flood or not to flood?
amount of precipitation
soil and underlying rock, (in)permeable
land use of river basin, e.g. vegetation
human activity, e.g. deforestation, concrete, (low infiltration and more run-off
steep/flat slopes
rainfall duration, e.g. fast & heavy (flood), long & light (no flood)
how deep soil is
processes in upper/middle/lower course
upper: vertical erosion
middle: vertical + lateral erosion
lower: deposition
valley shape in upper/middle/lower course
upper: v shaped
middle: }
lower: wider }
velocity in upper/middle/lower course
upper: 2nd fastest (bc lots of friction)
middle: fastest (no friction)
lower: slowest (flat gradient)
land forms in upper/middle/lower course
upper: waterfalls, rapids(small waterfalls), potholes, v shaped valleys, gorges
middle: erosion/deposition, meander, ox bow lakes, flood plain
lower: levees, flood plains, deltas, salt marshes
what is
long profile
river from its source to mouth
case study
river flood management
Danube, Ulm, Germany
cycle path on raised ground - levee
Friedrichschau - recreation, low value, not protected, used as place for flooding (spreading ground - flood without financial lost)
concrete flood protection wall (not everywhere bc it’s ugly & expensive
man-made piles of stones protects river bank from erosion (cheaper & prettier than a wall, & dissipation of energy)
dredging - making river deeper (reducing friction makes it faster)
cheap stone cages that prevent flood (gabian walls)
river is straightened (no meander) - protects buildings, gets water out quickly
thalfingen dam - controls water levels, electricity
what is coral reef and coral?
coral reef: line of coral polyp in warm shallow seas
coral: tiny carnivore animals
where is coral reef found?
within tropics
high sea temperature
shallow water
clear water (so sunlight reaches them)
3 types of reefs
fringing reef: close to coast & only separated by small stretch of water
barrier reef: larger reefs, parallel to coast, and separated by shallow seas
atolls: near surface of sea when islands surrounded by reef subside
why are coral reef so important?
support 25% of marine species protect coastline from erosion natural recycling agent from CO2 contribute as material to formation of beaches raw material (jewellery, ornaments) compounds useful in medicine
how are coral threatened?
increase in tourism people diving motor boats overfishing upsets food chain of choral pollution disposed in sea, pesticides global warming affects water temp and depth hurricanes, storms
how can we protect coral?
banning damaging fishing practices conservation zones where tourism isn't allowed no farming of coral banning dropping of anchors near reduce use of fertilisers near educating people
how do sand dunes & salt marshes form?
strong winds, large expanses id dry sand, and small grains cause saltation & sand moves up the beach
something stops sand from moving (seaweed, vegetation, or rubbish) and traps it
embryo dunes are the first, they are made stable by marram and lyme grass
they grow into yellow dunes (due to lack of humus) then into foredunes (great amount of humus)
sand dunes are destroyed by humans as they walk/build on them
dune slacks: depressions between dune ridges, damp in summer, & water-filled in winter
blow outs: holes, often evidence of over use by humans
what are some cost management methods?
sea walls - ugly, expensive, strong
revetments - don’t last long, ugly, but wave will go through but lose energy & traps sand
breakwaters
gryones
gabions
rip rap
