River Environments - River and Landforms Flashcards
Define stores
features such as lakes and rivers which receive, hold and release water
Define groundwater
water contained in the soil or underlying rocks, derived mainly from percolation
Define transfers
the movement of water between stores in the hydrological cycle
Define evapotranspiration
The loss of moisture from the ground through the direct evaporation of water from the soil as well as transpiration from plants
Infiltration and percolation
the transfer of water downwards through soil and rock and into an aquifer/groundwater store
Throughflow
takes place between the ground surface and the groundwater store; water moves slowly through the soil until it reaches a water body due to gravity
Groundwater flow
happens in rock in aquifers and is the underground transfer of water to rivers, lakes, sea, etc
Why is the hydrological cycle a closed system?
because it contains a fixed amount of water, as no water enters or leaves the atmosphere
why is a drainage basin an open system
because it has external inputs and outputs, with the amount of water in the basin system varying over time
inputs of a drainage basin
energy from the sun
precipitation from moisture picked up outside the basin
water from tributary drainage basins
outputs of a drainage basin
the river’s discharge
water in the basin which enters the atmosphere through evaporation/transpiration
define discharge
the quantity of water flowing in a river channel in a particular location and time
watershed
the boundary between neighbouring drainage basins
estuary
the mouth of a river as it enters the sea
channel network
the system of surface and underground channels that collect and transport the precipitation falling on the drainage basin
factors influencing drainage density of a river basin
size, shape, rock type, soil type, relief, land use, vegetation
define river regime
the seasonal variations in the discharge of a river
what is a hydrograph
a graph showing the discharge of a river over a given period of time
unit for discharge
cumecs (cubic metres per second)
define lag time
the delay between peak rainfall and peak discharge
storm hydrograph
records the changing discharge of a river after a rainstorm
define base flow
the usual discharge of a river
define storm flow
the additional discharge of a river as a result of a rainstorm
6 factors affecting river regimes and storm hydrographs
- amount and intensity of rain
- temperature affecting the form of precipitation and may affect throughflow and run off
- steep vs gentle slopes
- vegetation and land use (plants intercept and delay rain from reaching the ground whereas bare soil and concrete speed up run off and reduces lag time)
- human intervention (dams and reservoirs can hold back discharge, decreasing the risk of flooding downstream)
5 processes which play a part in shaping landforms (3 of them are river processes)
- erosion
- transport
- deposition
- weathering
- mass movement
explain physical weathering
this breaks rock down into smaller pieces; it is done by changes in temperature and rainfall freezing and thawing in rock cracks
explain chemical weathering
this causes rocks to decay and disintegrate; largely done by slightly acidic rain seeping into porous rocks
explain biological weathering
the roots of plants growing into cracks in rocks gradually split the rock apart
two forms of mass movement
- slumping
- soil creep
explain slumping
this occurs when the bottom of a valley side slope is cut away by the river, making the slope unstable and causing weathered material to slump down towards the river
this is also helped when weathered material on the slope is saturated with rain, which makes it heavier and acts as a lubricant
explain soil creep
where weathered material moves slowly down the slope under the influence of gravity, collecting at the base and being eroded by the river
4 methods of erosion
hydraulic action
abrasion
corrosion/solution
attrition
explain hydraulic action
water hits the river bed with enough force that the material is dislodged and carried away
explain abrasion
material carried by a river is rubbed against the sides and floor of the channel, widening and deepening the channel
explain corrosion
minerals in the rocks of the river channel are dissolved by the water flowing past them
explain attrition
particles being carried by the river become rounder and smaller as they collide with each other
4 methods of transport
traction
saltation
suspension
solution
explain traction
when large rocks or boulders are rolled along the river bed
explain saltation
when small boulders are bounced along the river bed
explain suspension
where lighter material is carried by the river flow
explain solution
where material is transported as it is dissolved in the water
what is deposition
the laying down of material transported by the river; it occurs when there is a decrease in energy, speed and discharge
it is most likely to happen at the mouth of a river or where there is a decrease in the gradient of the river channel
long profile
the section through a river or glacier course, from its source to its mouth
things which increase as you go downstream in the long profile
discharge
occupied channel width
channel depth
average velocity
load quantity
things which decrease as you go downstream in the river profile
load particle size
channel bed roughness
slope angle (gradient)
describe the upper course of the river
long profile is steep
river flows fast
most of the river’s energy is spent on vertical erosion
hydraulic action and abrasion erode the river bed and make the valley deeper
mass movement down slopes of valley due to its steepness and depth
valley floor is narrow and usually completely occupied by river
describe the lower course of a river
river channel and valley become wider, deeper and smoother
river velocity and discharge continue to increase
valley cross-section is wider and flatter
valley floor is occupied by flood plain
formation of interlocking spurs
streams in the upper course are not strong enough to erode into interlocking hills, so they have to flow around them instead
upper course landforms
interlocking spurs
steep V-shaped valleys
waterfalls
gorges
formation of waterfalls
- they occur where a band of hard rock meets a band of soft rock
- the softer rock is readily eroded by the force of the water as it fall over the hard cap rock
- plunge pool is excavated at the bottom of the falls by the falling water
- softer rock under hard rock is eroded by hydraulic action and abrasion, undercutting the hard rock
- the hard rock overhangs until it cannot carry its own weight
- overhang collapses and breaks up in the river below, causing the gorge to retreat
- gorge is prevented from widening by the hard cap rock
lowland landforms
levees
deltas
meanders
flood plains
ox-bow lakes
formation of levees
sediment is deposited on the flood plain when the river leaves its channel, as the velocity decreases when the river returns to its channel, causing the most sediment to be deposited on the river banks
formation of meanders
the river flows faster on the outside of bends and faster on the inside of them, causing lateral erosion on the outside of the bends and deposition on the inside of them
formation of ox-bow lakes
eventually the neck of a meander is eroded so much that the river flows straight again, cutting off the meander from the rest of the river as deposition during flooding seals the ends of the meander. This cut off meander is known as an ox-bow lake
deltas
these are vast areas of alluvium at the mouths of rivers, which are deposited sediment carried by the river as it flows into the sea, decreasing its velocity
the load is dropped faster than tides can wash it away, blocking the river flow, so the river splits up into smaller channels known as distributaries, which deposit sediment over a wide area to create new land where there was once sea
