Rivers Flashcards
define drainage basin
an area of land drained by a river and its tributaries
define watershed
the border between drainage basins E.g hills
source of a river
the beginning of the river
mouth of a river
the end of the river
where it meets the sea
what is a confluence
where 2 rivers meet
what is a tributary
when a smaller river joins a larger river
river channel
the area the water takes up
where does vertical erosion occur and what does it form
occurs in the upper course
forms V-shaped valleys
where does lateral erosion occur and what does it form
occurs in the middle & lower course
forms wide valleys
when does a river deposit material
- going around a bend- material deposited on inside bend
- during flooding
- at the mouth when freshwater meets seawater- mudflats are formed
-at the end of the river
what is a long profile
describe the long profile of a river
shows changes in the height of the course of a river from its source to its mouth
Upper course - river’s load is large as it hasn’t been broken down by erosion yet. narrow valley sides
Lower course - land is flatter. river’s load is fine sediment, as erosion has broken down the rocks.
what is a cross profile
describe the cross profile of a river
show a river’s cross section as it changes with distance downstream
upper course- narrow and steep-sided river channel due to vertical erosion
middle course- wider valley floor due to more lateral erosion than vertical erosion
lower course- almost flat valley floor, only some lateral erosion, river at its widest
fluvial processes
processes found in a river
what is erosion
describe the 4 types of erosion
erosion is the process which wears away the river bed and bank
- hydraulic action- power of water as it smashes against river banks. Air gets trapped in cracks of river bank and bed, causing the rock to break apart
2.abrasion- pebbles grind along the river bank and bed in a sand-papering effect.
3.attrition- rocks carried by the river hit each other. They break apart to become smaller and more rounded
4.solution- the water dissolves certain types of rocks, eg limestone
what is transportation
describe the 4 types of transportation
transportation is when the river picks up sediment and carries it downstream.
- traction- large, heavy pebbles are rolled along the river bed- most common near source of a river as load is larger.
- saltation- pebbles bounce along the river bed, most common near source
- suspension- lighter sediment is carried within the water, most common near mouth of the river.
- solution- transporting dissolved chemicals
define load
the particles of rock carried by a river
describe deposition
when does deposition occur
deposition is when the river loses energy and drops material
-shallow water
-at the river’s mouth
-when volume of the water decreases
-areas of low velocity
what landforms result from erosion
waterfalls
gorges
interlocking spurs
what landforms result from erosion and deposition
meanders
oxbow lakes
what landforms result from deposition
levées
floodplains
estuaries
explain the formation of a waterfall and gorge
where are waterfalls found
found in upper course
- soft rock is eroded quicker than hard rock
- hard rock is undercut by erosion (hydraulic action & abrasion), forming an overhang
- this forms a plunge pool
4.plunge pool gets bigger and overhang collapses
5.process continues and waterfall retreats upstream
- A steep-sided valley is left where the waterfall was. This is a gorge.
explain the formation of interlocking spurs
where are interlocking spurs found
found in upper course
In upper course there’s more vertical erosion.
the river bends round areas of hard rock instead of eroding them
This creates interlocking spurs of land which link together
explain the formation of a meander
where are meanders found
in middle & lower course
As river goes around bends, water is pushed towards the outside.
This increases speed and increases erosion (hydraulic action and abrasion).
lateral erosion on outside bend undercuts the bank to form a river cliff.
Water on inner bend is slower, so water slows down and deposits material,
creates a slope of sand and shingle.
The build-up of deposited sediment is a slip-off slope/river beach.
explain the formation of an oxbow lake
in middle and lower course
meander neck narrows due to lateral erosion
during high river discharge, meander neck breaks.
river takes the shorter, straight route
deposition at the edges cuts off the old meander
the old meander forms an oxbow lake, is horseshoe shaped- separate to river
oxbow lake silts up to form marshland
explain the formation of a levée
where are levees found
found in lower course
during high river discharge and flooding
Sediment eroded upstream is transported downstream.
during floods, the river loses energy.
large material is deposited first on the sides of the river banks and small material deposited further away.
After many floods, sediment builds up to increase height of the river banks,
the channel can carry a greater discharge
flooding is less likely to occur in the future
explain the formation of floodplain
in middle and lower course
A floodplain is an area of land covered in water when a river bursts its banks.
Erosion removes interlocking spurs, creating a wide, flat area on both sides of the river.
During a flood, material carried by the river is deposited (as the river loses its speed and energy).
Over time, the height of the floodplain increases as material is deposited on either side of the river.
Floodplains are agricultural land, as the area is fertile because it’s made up of alluvium (deposited silt from a river flood).
explain the formation of a estuary
lower course
An estuary is where the river meets the sea. (mouth)
The river here is tidal and when the sea retreats, the volume of the water in the estuary is reduced.
When there is less water, the river deposits silt to form mudflats which are habitats for wildlife.
3 physical factors of floods
precipitation- heavy rainfall saturates soil so water cannot infiltrate into the soil = surface runoff
geology- impermeable rocks don’t let water infiltrate into them =surface runoff
steep slopes- causes rapid water transfer which means a SHORT LAG TIME
define lag time
the time taken between peak rainfall and peak discharge.
3 human factors of floods
farming- bare soils transfer water quickly, short lag time
urbanisation- construction using impermeable surfaces such as concrete, water cannot infiltrate
deforestation- trees intercept rainfall and reduce flood risk. if there are less trees, less rain is intercepted= higher flood risk
define peak discharge
the maximum amount of water held in the channel
define peak rainfall
the maximum amount of rainfall (mm)
define rising limb
the increase in discharge on a hydrograph
define falling limb
the return of discharge to normal/base flow on a hydrograph.
define base flow
the normal discharge of a river
what factors decrease lag time
large drainage basin
little vegetation
steep valley sides
impermeable soil type
what are hard engineering strategies
list the 4 hard engineering strategies
building artificial structures which try to control rivers.
-dams & reservoirs
-river straightening & dredging
-embankments
-flood relief channels
what are soft engineering strategies
list the 4 soft engineering strategies
takes a more sustainable & natural approach to managing river flooding
-flood warnings and preparations
-floodplain zoning
-planting trees
-river restoration
explain dams/reservoirs
gives advantages
give disadvantages
dam traps water, which builds up behind it, forming a reservoir. Water is released in a controlled way.
Advantages:
-Hydro-electric power
-water sports attract tourists
-creates wetland habitats
Disadvantages:
-Very expensive
-reservoir silts up which reduces storage capacity
-locals are displaced
-Habitats destroyed
explain river dredging/straightening
gives advantages
give disadvantages
Straightening the river speeds up water so high volumes of water can pass through an area quickly. Dredging deepens the river so it holds more water.
Advantages:
-More water held in the channel
It can be used to reduce flood risk in built-up areas.
Disadvantages:
-expensive
-faster water flow increases flood risk
explain embankments
gives advantages of
give disadvantages of
Raising the banks of a river means that it can hold more water.
Advantages:
-more water can be hold
-create walkways for locals .
Disadvantages:
-expensive
-Looks unnatural
explain flood relief channels
gives advantages
give disadvantages
The floodwater flows into the relief channel is taken to an area where it’s absorbed, or re-enters the river
Advantages:
-Removes excess water from the river channel
-recreation-walking, fishing
-aquatic habitats created
Disadvantages:
-Expensive to build
-can look unattractive
-regular maintenance needed
explain flood plain zoning
gives advantages
give disadvantages
restricts land uses in high-risk areas, high-value land uses away from flood-prone areas.
Advantages:
-expensive buildings & land uses are far from the river, so have a reduced flood risk.
-so less damage is caused, leading to fewer insurance claims.
Disadvantages:
-restricts economic development in areas as land use is prohibited
explain flood warnings and preparation
gives advantages
give disadvantages
EA issues online warnings about floods so people can evacuate
Advantages:
-gives time to evacuate and prepare
-possessions can be saved, fewer insurance claims.
Disadvantages:
-Some people may not be able to access the warnings.
-Flash floods- too quick too prepare for
-does not stop floods
explain planting trees
gives advantages
give disadvantages
trees intercept rainfall, reduces runoff
advantages:
-creates habitats
-reduces carbon emissions
-inexpensive
disadvantages:
-reduces biodiversity
-loss of farmland
explain river restoration
gives advantages
give disadvantages
restores straightened channels to meandering pattern to slow water flow.
advantages:
-restores wetland areas
-reduces downstream flooding
disadvantages:
-expensive to construct and maintain
Jubilee river
a flood relief channel on the River Thames, built in 2002
12km in length
50m wide
low flow conditions
removes excess water from thames
Jubilee river social issues
-protection of wealthy properties such as windsor, but not less affluent towns downstream
-paddle boaters are disrupted by weirs
Jubilee river economic issues
- cost £110 million
-floods damaged weirs- high maintenance cost
Jubilee river environmental issues
-flooding in 2014 damaged habitats
-concrete weirs are unattractive
-algae collects above weirs
describe the path of the river tees
River Tees is located in north of England.
The source of the River is located in the Pennines
river flows east to its mouth where it joins the North Sea
describe the upper course of the river tees
-Hard, impermeable rocks.
-interlocking spurs (cauldron snout)
-Vertical erosion formed a V-shaped valley.
-High Force (UK’s largest waterfall)
-area of hard rock, called
Whinstone is located above soft rock (limestone)
describe the middle course of the river tees
As the River Tees erodes sideways (lateral erosion), it forms meanders.
These are seen in the middle course near Barnard Castle.
describe the lower course of the river tees
-Near Yarm, meanders are larger, oxbow lakes have formed.
-levees have formed when the river has flooded.
-a very large estuary with mudflats and sandbanks which supports wildlife in the area.
Sites such as Seal Sands are protected areas.
define relief
the difference in heights of land’s surfaces
