Rivers Flashcards
(40 cards)
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
