River Landscapes Flashcards
what is the long profile of a river
the long profile takes the form of a concave curve. the steepest gradient is in the uplands near the source of the river. further downstream, the gradient is reduced
how does the cross profile change throughout the river
The channel becomes wider and deeper with the distance downstream
why does the upper course of the valley be narrow and steep sided
due to vertical erosion by the river combined with weathering and mass movement of the valley slopes
why does the middle course of the valley be wider
due to lateral erosion from meandering rivers
why does the lower course be wide and flat
sediment dumped by the river as it slows down and loses its energy
what is a fluvial process
river process
what are the three types of fluvial process
- erosion
- transportation
- deposition
what is hydraulic action
the power of flowing water to erode the river’s bed and banks
what is solution (the type of erosion)
dissolving of solubles in water such as limestone and chalk
what is traction (type of transportation)
large particles rolled along the river bed by the force of the water
what is saltation (type of transportation)
a bouncing or hopping motion by pebbles too heavy to be suspended
what is suspension (type of transportation)
particles suspended in the water
what is solution (type of transportation)
particles/chemicals dissolved in the water
what landforms result from river erosion
- interlocking spurs
- waterfalls
- gorges
where are interlocking spurs commonly found
in the upper course of the river
why do interlocking spurs occur
there is mostly vertical erosion rather than lateral in the upper course which means that the river is forced to flow around the jutting out pieces of land rather than cutting into them
what two erosion processes erode the plunge pool
- hydraulic action
- abrasion
Characteristics and formation of landforms resulting from erosion – interlocking spurs, waterfalls and gorges.
. - use rivers booklet
how are waterfalls created
- when water flows over hard rock then soft rock, the soft rock erodes faster through hydraulic action and abrasion to form a step
- the step is eroded further and deeper to form a plunge pool, as well as starting to undercut the rock
- the undercut leaves very little support for the hard rock so it cracks and falls into the plunge pool
- the fallen rock is used in abrasion which further erodes the plunge pool
the process repeats and the waterfall recedes upstream
what is a gorge
a steep sided valley where the river once was
how are meanders formed and why are slip off slopes formed
- most water is directed towards the outside of the bend which means it flows faster so had more energy - eroding fast
- the inside bend there fore has less water which means it is shallower, slower and has less energy so it deposits its material
- this builds up over time to form the slip off slope
where are meanders commonly found in a river course
middle and lower course
what are riffles and pools
the shallow and deep areas of a meander respectively
how are oxbow lakes formed
- the neck of the meander narrows due to erosion on opposite sides
- the neck is finally broken through and the water then adopts the shorter route
- deposition occurs at the edges and cuts off the old meander until it is completely separate
what are three landforms that result from deposition
- leveés
- flood plains
- estuaries
how do leveés form
when rivers flood:
- as the water overtops the river banks, there is a sudden localised drop in velocity of the water that had previously been flowing very fast along the river
- this causes sediment in suspension to be deposited at the river bank
- heavier sediment is deposited first and this traps the finer sediment
- with each successive flood the deposited material raises the river banks
what are flood plains and how do they form
- extensive, flat areas land mostly covered by grass
during a flood:
- water containing large quantities of alluvium (river silt) pours out over the flat valley floor
- the water slowly soaks away leaving behind the deposited sediment
- repeated flooding forms a thick alluvial deposit which is fertile and often used for farming
how are estuaries formed
- incoming tides force seawater and sediment up the river channel, mixing with river water flowing in the opposite direction
- where the fresh and salt water meet, velocity falls rapidly resulting in significant deposition
- over time these muddy sediments break the water surface to form extensive mudflats
- vegetation colonises the mudflats to form saltmarshes
characteristics of a waterfall
- a step in the long profile of a valley which fast flowing water falls off
- considerable drop
- deep plunge pool eroded by hydraulic action and abrasion
what is an estuary
where the freshwater of a river meets the sea (saltwater)
example of a waterfall along the River Tees
high force
where is the source of the River Tees
at Cross Fell in the Pennines
where along the river Tees can a meander be found
the town of Yarm is enclosed by a meander on 3 sides
list all the major landforms of erosion and deposition along the River Tees
it has all the landforms that we study:::
- source
- v-shaped valleys and interlocking spurs
- waterfall
- floodplains and meanders
- leveés
- estuary
what physical factors affect the flood risk of an area
- heavy or prolonged precipitation
- impermeable rock
- steep slopes (water travels fast down slopes and also collects in one area instead of being spread out)
what human factors affect the flood risk of a river
- deforestation (not being used as well as not being caught by their umbrellas)
- urbanisation (concrete)
- farming (bare soils transfer water quickly, ploughing creates runnels for water to rapidly flow through)
what is a hydrograph
a graph to show how much water gets into a river after a rain storm
what are four hard engineering strategies for flood management
- dams and reservoirs
- channel straightening
- embankments
- flood relief channels
benefits of building a dam/reservoir - flood management
- hydroelectric power
- recreation
- wetland habitats
- source of drinking water
costs of building a dam/reservoir - flood management
- high costs
- loss of farmland and homes and habitats(flooded area)
- can affect migrating fish
how does channel straightening help to prevent floods
cutting of meanders to create a more efficient channel better suited to the rapid transfer of water
costs of channel straightening - flood management
- increases flood risk downstream in meandering sections
- can be expensive and high maintenance
- aquatic life affected by change in velocity of the water
benefits of channel straightening - flood management
- effective
- insurance premiums may be reduced for home owners
- navigation improved
how do embankments help to prevent flooding
increase the amount of water the river can hold by building up the sides of the river
costs of embankments - flood management
- can be expensive
- look artificial and unattractive
- more serious flooding if the embankment fails
benefits of embankments - flood management
- river channel has an increased capacity for carrying water
- create walkways
- new river bank habitats can be created
costs of flood relief channels - flood management
- expensive
- regular maintenance is required
- habitats may be disturbed
benefits of flood relief channels - flood management
- be very effective in reducing risk in high value areas
- new recreational opportunities
- new aquatic habitats
- insurance premiums reduced
examples of soft engineering strategies for reducing flood risk
- flood warnings
- floodplain zoning
- planting trees
- river restoration
costs of flood warnings - flood management
- need for monitoring equipment, scientific expertise
- people might not respond and react appropriately
benefits of flood warnings - flood management
- sustainable
- safety at a lower cost
what is floodplain zoning - flood management
local planning to restrict land uses in high-risk areas
costs of floodplain management - flood management
- restricts economic development
- hard to implement when urban developments have already taken place there
- land could be used to alleviate housing shortages
benefits of floodplain management
- low cost
- protects and conserves wildlife habitats
- reduces additional impermeable surface coverage
how does planting trees help reduce flooding
increases the interception and also absorb it to use themselves
disadvantages of planting trees - flood management
- can reduce habitat diversity
- loss of potential farmland
- can lead to increased acidity in soils
benefits of planting trees - flood management
- creates habitats
- natural method
- helps to absorb carbon
- relatively inexpensive
what does river restoration involve - flood management
creating meanders to slow down water flow. this increases risk of flooding in that area but decreases the risk downstream
costs of river restoration (putting a meander into the river) - flood management
- can be expensive to construct and maintain
- change in land use
- creates more flooding in that area which can inconvenience people trying to use the land
benefits of river restoration - flood management
- recreates a natural, attractive environment
- effective
- restores wetland areas, increasing biodiversity
location of York
in the north of england at the confluence of the River Ouse and river Foss
why was a flood management scheme required in York
- York regularly floods: serious flooding has occurred in six of the last 60 years
- the floods in 2000 were the worst on record
facts about the flood in York in 2000
- over 500 properties flooded
- 19,000 hectares of farmland affected
- ouse rose 5.5 meters above its normal level
what management strategies were put in place for flooding in York
- the Foss Barrier
- Embankments at Leeman Road
- Floodplain zoning: Clifton Ings
- Flood relief channels around acomb
- Flood gates on Marygate
what did the Foss barrier do
built to prevent water from the River Ouse backing up the River Foss
what do the embankments at Leeman road do
increase the capacity of the river channel
what has happened at Clifton Ings to prevent flooding
floodplain zoning
it has been left as an open, undeveloped floodplain that can store millions of meters of water
what do the flood relief channels around Acomb do
divert water directly into the Ouse downstream of York
what were the social issues with the flood management schemes in York
- reduced risk of flooding
- transport disruption during times of flood reduced
- cycleway made wider and resurfaced
what were the environmental issues with the flood management schemes in York
- some habitat destruction needed
- however two ponds were created which have created new wetland habitats
what were the economic issues with the flood management schemes in York
Foss Barrier upgrade cost more than double what was estimated
- total cost estimated £83 million
however
- increased potection for homes and businesses
- lower insurance premiums
