River Land Forms- The River Valley Flashcards
what is the course
the path of a river as it flows downhill
features found in the upper course of a river
steep gradient
v shape valley
shallow chanell
fast flowing water
erosional processes
waterfalls
gorges
features found in the middle course of a river
medium gradient
gently sloing valley
meanders
ox-bow lakes
levees
deeper channel
features found in the lowe course of a river
gentle gradient
very wide channel
deep channel
estuaries
mouth of the river
vertical erosion
erosion that deepens the river valley and channel causing V-shaped valleys.
found in the upper course of a river.
high turbulence of the water causes the rough angular particles to be scraped along river bed,
lateral erosion
widens the river valley and channel during formation of meanders.
usually in middle and lower courses of the river
hydraulic action
the force of the river water colliding with rocks breaks rock particles away from the river channel
abrasion
eroded rocks picked up the river scrape and rub against the channel wearing it away.
most erosion happens by abrasion
attrition
eroded rocks picked up by river crash into each other and break into smaller pieces
causes particle size to decrease from source to mouth
solution
river water dissolves some type of rock (chalk and limestone)
traction
large particles are pushed along the river bed by water force
saltation
pebble sized particles are bounced along the river bed by force of water
suspension
small particles (silt, clay) a carried by the water
solution
soluble materials (limestone) dissolve and are carried by the water
deposition
.a river drops eroded material
.occurs when river loses velocity and energy
dominant in lower course
why do rivers slow down and deposit material
.volume of water falls
. the amount of eroded material increases
. the water is shallower
the river reaches mouth
how are waterfalls formed
1.)when a river flows over an area of hard rock
2.) the softer rock is eroded(hydraulic action and abrasion) forming a step in river
3.) over time, a steep drop is created (waterfall)
4.) hard rock undercut by erosional processes- collapses
5.)
how is a plunge pool created
hard collapsed rocks undercut the soft rock at the bottom of the waterfall, via vertical abrasion
how is a gorge formed
over time more undercutting leads to waterfall being pushed back, causing behind a steep gorge
what a meanders
large bends in a river
found in the middle and lower courses in a river formed by erosion and deposition
how are meanders formed
1.)current is faster on the outside of the bend (river channel is deeper)
2.) more erosion takes place on the outside of a bend- forming river cliffs
3.) current is slower on the inside bend of a river, because river channel is slower
4.) more material is deposited on the inside of the bend, forming slip of slopes
how are ox-bow lakes formed
1.)erosion over times causes the inside bends to get closer until only a small bit of land between rock (neck)
2.) river breaks through this land and flows through the shortest course
3.) deposition over time cuts of meander, forming an ox-bow lake
flood plain
wide valley floor on each side of the river that flood
found in middle and lower courses of river
how do flood plains build up
when rivers flood, water slows down losing energy and deposits material on each side of the river- building up the flood plain
deposition that happens on the slip of slope of meanders build up the flood plain
levees
natural embankments along the edges of a river channel
how to levees build up
during a flood, eroded material is deposited over whole flood plain
over time deposited material builds up, creating levees along the edges of the channel
esturies
tidal areas where the river meets the sea
found in the lower course of a river
estuary water is tidal- water level rises and falls each day
river discharge
the volume of water flowing in a river per second
what is river discharge measured in
cumecs (cubic metres per second
hydrographs
show how the discharge at a certain point in a river changes in relation to rainfall
1.) peak discharge
the highest discharge in the period of time that is being recorded
2.) lag time
the delay between peak rainfall and peak discharge
3.)rising limb-
the increase in river discharge as the river returns to normal level
4.)falling limb-
the decrease in river discharge as the river returns to normal level
how is lag time affected by physical and human factors
lag time occurs because most rainfall doesnt land in a river channel
either flows as surface runoff or soaks into the ground (infriltration)
Heavy rainfall
Heavy rainfall means that water arrives too quickly to infriltrate, so there is more surface runoff- increases discharge
geology
clay soils and some rocks (granite) are impermeable(don’t allow infiltration) so runoff is increased
prolonged rainfall
prolonged rainfall can saturate the soil. Any further rainfall cannot infiltrate, increasing runoff in river channels
relief (changes in land heights)
if a river is in a steep sided valley, water will reach river channel quicker increases discharge
Hard engineering
.Man made structures built to control water the flow of rivers and reduce flooding
This can reduce the risk of flooding
What Dams and reservoirs
Barriers built across rivers
Found in the upper course
Reservoirs are artificial lakes formed behind a dam
Benefits of dams and resovoirs
Reservoirs store water after heavy rain, control water flow and prevent flood’s downstream
Generate hydroelectric power
Disadvantages of dams and reservoirs
Dams are very expensive to build.
Reservoirs can flood existing settlements
Material is deposited in the reservoir,. So farmland downstream can become less fertile.
What is channel straightening
Meanders are removed by building artificial straighter channels
Benefits of channel straightening
Water leaves the area more quickly so flood risk is lower
Disadvantages of channel straightening
Flooding may happen downstream instead.
Faster moving water causes erosion downstream
What are embankments
Raised walls are built along river banks
Advantage of embankments
River can hold more water so floods are less frequent
Disadvantages of embankments
Very expensive
Risk of severe flooding if water rises above level of embankment
Flood relief channel
Channels are built to divert water around Built up areas to divert excess water if level gets to high
Benefits of flood river channel
Gates on the channel mean the release of water can be contolled- reducing flood risk
Disadvantages of flood relief channels
Increased discharge where the relief channel rejoins the river- causing flooding in that area
Soft engineering
Schemes set up using knowledge of a river and its processes to reduce the effects of flooding
Reduce effects of flooding
What is Flood warning and preparation
Environment agency issues flood warning through forms of media eg radio, tv.
Buildings are modified to minimise flood damage- residents also prepare sandbags and boards prior to flooding
Benefits of flood warnings and preparation
Residents have more time to prepare and move possessions upstairs use sandbags etc
This reduces impact of flooding
Disadvantages of flood warnings and preparation
Warnings don’t prevent actual floods
People may not have access to the warnings
Expensive to modifying buildings
Flood plain zoning
Restrictions prevent building on parts of flood zone that are likely to affected by a flood
Benefits of flood plain zoning
Flood risk is reduced (fewer impermeable surfaces are created)
Impact or flooding is reduced
(No buildings to damage)
Disadvantages of flood plain zoning
Expansion of urban is limited
Can’t help in existing buildings
Planting trees
Planting trees in the river valley increases interception of rainwater
Benefits of planting treesc
Discharge and flood risk decrease
Vegetation reduces soil erosion- provides habitats for wildlife
Disadvantages of planting trees
Less land available for farming
River restoration
Making river more natural, by removing man made levees, so plain can flood naturally
Benefits of river restoration
Discharge is reduced so there’s less risk of flooding downstream
Little maintenance is needed
Disadvantages of river restoration
Local flood risk can increase. Especially if nothing is done to prevent flooding
