rivers Flashcards
upper course gradient, valley and channel shape
steep gradient, v-shaped valley, narrow and shallow channel
middle course gradient, valley and channel shape
medium gradient, gently sloping valley side, deeper channel
lower course gradient, valley and channel shape
gentle gradient, almost flat valley, wide and deep channel
vertical erosions
deepens the river valley and channel making v-shaped
lateral erosion
widen the river valley and channel
4 processes of erosion
-hydraulic action
-abrasion
-attrition
-solution
hydraulic action
force of the river water colliding with rocks breaks rock away from the river channel
abrasion
eroded rocks picked up by the river scrape and rub along the channel, wearing it away
attrition
eroded rocks picked up by the river crash into each other and break into smaller fragments
solution
river water dissolved some types of rock
4 processes of transportation
-traction
-suspension
-saltation
-solution
traction
large particles are pushed along the river bed by the force of the water
suspension
small particles like silt and clay are carried along by the water
saltation
pebble-sized particles are bounced along the river bed by the force of the water
solution
soluble materials dissolve in the water and are carried along
what is deposition
when a river drops the material it’s transporting
why does deposition occur
when the river loses velocity and energy
how does particle size affect deposition
smaller particles are transported further and are deposited closer to the river’s mouth
formation of waterfalls
-softer rock is eroded more than the hard rock, creating a step
-a steep drop is eventually created, a waterfall
formation of gorges
-hard rock is eventually undercut by erosion, it becomes unsupported and collapses
-the collapsed rock erodes the softer rock by abrasion creating a deep plunge pool
-more undercutting causes more to collapse. The waterfall retreats leaving behind a steep sided gorge
interlocking spurs
-in the upper course of a river most of the erosion is vertical, creating v-shaped valleys.
-the river doesn’t have enough power to erode laterally so they have to wind around the hillsides
landforms formed by erosion
waterfalls, gorges and interlocking spurs
landforms formed by erosion and deposition
meanders and oxbow lakes
how are meanders formed
-the current is faster on the outside of the bend because the river channel is deeper
-more erosion takes place on the outside of the bend forming river cliffs
-the current is slower on the inside of the bend because the river channel is shallower, so eroded material is deposited on the inside of the bend, forming slip-off slopes
oxbow lake formation
-meanders get larger over time, erosion causes the outside bends to get closer
-the river breaks through the small bit of land in between and the river follows the shortest course
-deposition eventually cuts off the meander forming an oxbow lake
landforms formed by deposition
-levees, flood plains and estuaries
floodplains
-the wide valley floor on either side of a river which occasionally floods
-when rivers flood, the water slows down, loses energy and deposits the material that its transporting
levees
-natural embankments along the edges of a river channel
-during a flood, eroded material is deposited closest to the river channel because it get dropped first when the river slows down and loses energy
-the deposited material builds up creating levees along the edges of the channel
estuaries
-found a the mouth of the river
-when the water floods over the banks of the river it carries silt and sand onto the valley floor
-as the tide reaches its highest point, the water moves slowly and has little energy so it deposits sediment
-over time, more mud builds up creating large mudflats
-at low tide the muddy banks are exposed
physical factors affecting flood risk, 4
-heavy rainfall
-geology
-prolonged rainfall
-relief
human factors affecting flood risk
-land use
how does land use affect flood risk
-buildings made from impermeable materials increase surface runoff, man-made drains transport runoff to rivers, increasing discharge
-trees intercept rainwater on their leaves which then evaporates, cutting down trees increases the volume of water that enters the channel
peak discharge
highest discharge in the period of time
lag time
delay between peak rainfall and peak discharge
rising limb
increase in river discharge as rainwater flows into the river
falling limb
decrease in river discharge as the river returns to its normal level
why does lag time occur
most rainwater doesn’t land directly in the river channel, it flows quickly overland or soaks into the ground then flows to the channel
what is hard engineering
man-made structures built to control the flow of rivers and reducing flooding
hard engineering strategies
-dams and reservoirs
-channel straightening
-embankments
-flood relief channels
what are flood relief channels
-channels built to divert water around built-up areas or to divert excess water if the river level gets too high
benefits of dams and reservoirs
-used to generate hydroelectric power
-prevent floods downstream
benefits of channel straightening
water leaves the area more quickly rather than building up
benefits of embankments
the river can hold more water, less flooding
benefits of flood relief channels
gates on the channels mean that the release of water can be controlled
dams and reservoirs disadvantages
-expensive
-floods existing settlements
channel straightening disadvantages
-flooding downstream instead
-faster-moving water may cause erosion downstream
embankments disadvantages
-expensive
-severe flooding if the water level rises or if they break
flood relief channel disadvantages
-increased discharge where the relief channel rejoins the river could cause flooding
what is soft engineering
schemes set up using knowledge of a river and its processes to reduce the effects of flooding
soft engineering strategies
-flood warnings and preparation
-flood plain zoning
-planting trees
-river restoration
benefits of flood warnings and preparation
warnings give people time to move possessions and evacuate
benefits of flood plain zoning
fewer impermeable surfaces created, no buildings to damage
benefits of planting trees
discharge and flood risk decreased
reduces soil erosion creating habitats
benefits of river restoration
less risk of flooding downstream, little maintenance needed
flood warnings and preparation disadvantages
warnings don’t prevent floods, expensive
flood plain zoning disadvantages
expansion of an urban area is limited if there aren’t any suitable building sites
planting trees disadvantages
less land is available for farming
river restoration disadvantages
local flood risk can increase
why was a flood management scheme needed on the river tees
-the steep v-shaped valleys in the upper course of the river are made of impermeable rock, increasing run-off and causing river levels to rise
-almost 23,500 people at risk of flooding
river tees management strategies (6)
-flood gates
-gabions
-flood warnings
-flood plain zoning
-the Tees barrage
-Cow Green reservoir
river tees flood management - social issues
-hard engineering is unattractive
-flooding continues to disrupt
river tees flood management - economic issues
-tees barrage cost £54 million
-flood defences are expensive to maintain
river tees flood management - environmental issues
-28 environmentally designated sights in the area at risk from flooding that require protection
