River Landscapes Flashcards
Size and shape of the source
Narrow v-shaped valley
Size and shape of middle reaches
Flat and broad v-shaped valley
Size and shape of mouth
Wide and deep
Landforms of the source
- v-shaped valley
- gorge
- waterfall
Landforms of middle reaches
- meanders
* ox-bow lake
Landforms of mouth
• estuary
Processes at the mouth
- erosion
* large sharp bedload
Processes at the middle reaches
- erosion
* depositing small rock
Processes at the mouth
• depositing fine material
Where is the river tees source?
Cross fell, in an area above 300m
What landforms are at the middle reaches of the river tees?
Meanders, ox-bow lakes, there are many meanders around the town of Yarm
What landforms are there in the upper-valley of the tees?
V-shaped valley, interlocking spurs, and many small tributaries and streams
What is at the estuary of the river tees ?
One of the largest container ports in the U.K.
The source of the river tees
- there is a cow green reservoir
- there is a nature reserve
- not many meanders
- sinuosity of 1.41
- v-shaped valley
- a high force waterfall
Middle course of the river tees
- has 10 meanders
- sinuosity of 3.64
- there are campsites,farms and woodlands e.g. Low hail farm
- meanders around a town called hurworth on tees
Mouth of the tees
- it widens and enters a industrial area
- there are oil terminal,car depot, steel works and chemical works
- surrounded by dunes and mud sands called seal sands
About the river tees waterfall
- it’s called high force waterfall
* it has a whinstone ontop of limestone
Changes in the river tees course
1) river flows straight although two meanders one going around crockley pasture
2) v-shaped valley and high force waterfall
3) gains a tributary in upper course called harwood been
4) middle course has many meanders and prone to flooding due to flat land
5) this causes ox bow lakes
6) river widens at mouth where it meets tees bay
7) mud and sand lands and enters industrial businesses
Abrasion
Rocks carried along by the river wearing down the river bed and banks
Attrition
Rocks carried along by the river smashed together and break into smaller smoother rocks
Hydraulic action
the motion of the water against a rock surface causes it to wear down
Vertical erosion
Erosion of the river bed which makes a deeper river
Lateral erosion
Erosion that occurred on the side of a river and makes it wider
Traction
Large boulders and rocks are rolled along the river bed
Saltation
Small pebbles and stones are bounced along the river bed
Solution
Minerals are dissolved in the water and carried along in solution
Suspension
Fine light material is carried along in the water of the river
Deposition
The process where material is transported by a river and is deposited somewhere else
Why does the deposition occur?
A river deposit sediment where the velocity of the river drops
How do pot holes occur ?
Potholes form when boulders pebbles and sand have swirled around in the plunge pool and caused a circular hole
How do waterfalls occur?
- hard rock overlies soft rock
- hydraulic action and abrasion occur eroding the soft rock quicker than the hard rock
- this creates an overhang
- overhang collapses
- waterfall retreats upstream when repeated
How do v-shaped valleys occur?
- vertical erosion occurs due to abrasion and hydraulic action
- sides of the river are steep and unsupported
- sides are weakened by weathering
- they break off and create a v-shaped valley
Interlocking spurs
The land has rocks various resistances, river wind its way around the more resistant rock and cuts down into the weaker rock leaving interlocking spurs
How do meanders occur?
- fast flowing water on the outside bank causes lateral erosion through abrasion and hydraulic action widening the river
- the slow flowing inner part of the river deposits silt and builds up a curve creating a slip off slope
How does a oxbow lake occur?
- the river erodes the outside bank of a meander leaving a narrow neck
- when the river floods the main flow cuts across the neck, this breaks down the neck and carves a new channel
- this process is repeated
- every flood causes lateral and vertical erosion at the neck and becomes the main channel
- the loop of the old river channel becomes detached by no longer receiving water and deposition on the banks
- leaving an ox-bow lake
How do levees occur?
- the river floods and the sediment that was in the river is washed up onto the sides of the flood plain
- every flood raises the river bank by deposition and creates levees
- the river bed builds up deposit over time increasing the chance of floods
Flood plain
A relatively flat area forming the valley floor on either side of a river channel which is sometimes flooded
Why are flood plains good for farming?
When the floods have receded the flood pain is slightly higher and more fertile due to the deposit of silt caused by the river flooding
What causes a bigger floodplain?
Meander migration
- more meanders = bigger floodplain
Estuaries
The title mouth of a river where it meets the sea
Characteristics of an estuarie
- high tidal range
- very wide
- mudflats
- tidal bores
How does an estuary occur ?
- salinity increases towards the sea
- there are two sources of sediment from the river and the sea
- The Estuary is tidal so fluvial and marine processes occur
- can also occur from an ice age
• after the ice age melting ice caused a rise in sea level this caused low-lying valley sides either side of the river to become flooded
Physical factors affecting flood risk
• precipitation - amount - type - duration • relief • vegetation -type -cover • geology
Human factors affecting flood risk
- urbanisation
- deforestation
- increase in population density
- changes in farming
- land use
Factors of high flood risk
- lots of surface run-off
- cities
- road and buildings
- heavy rainfall
- frozen ground
- impermeable rock
Factors of low flood risk
- permeable rock
- forests
- countryside
- dam on river
- little surface run off
Hydrograph
Shows the discharge of the river related to the rainfall over a period of time
What does a ‘likely to flood’ hydrograph look like ?
- steep rising limb
- high peak discharge
- short lag time
What does an ‘unlikely to flood’ hydrograph look like ?
- gentle rising limb
- low peak discharge
- long lag time
Discharge
The amount of water flowing through a river at any one time
How can discharge be measured ?
Discharge = cross sectional area
X velocity
Lag time
Difference between peak rainfall and peak discharge
What is hard engineering?
Uses heavy machinery to build artificial structures which worked against nature to reduce the risk of flooding
What is a Dam and reservoir
Restricts water using a concrete barrier
Benefits of dams and reservoir
- affective against flooding
- source of drinking water
- provides hydroelectric power
- promotes new habitats
- can be used for water sports
Disadvantages of dams and reservoir
- expensive and ugly
- costs £170 million
- soil downstream can become less fertile
- interfere with migrating fish
What is channel straightening
Make a widened, straightened
And deeper course
Benefits of channel straightening
- reduces flood risk
- faster-flowing water removes sediment which would increase the risk of flooding
- improves navigation
Disadvantages of Chanel straightening
- water flows fast through a straight section however when meets a meander floods the banks
- expensive £5.8 million
- £1.2 million was spent in lewisham putting meanders back in
- floods downstream endangering animals
- concrete lining is unattractive
What is embankment ?
Artificially raised river bank
Benefits of embankment
- safer from flooding
- habitats for riverbank animals
- walking routes created
- cheap
Disadvantages of embankment
- stops easy access for fishing
- false sense of security which means they may not be prepared for floods
- high macitence costs
- unattractive
- when floods takes a long time to drain back
What is a flood relief channel ?
And artificial channel that is designed as a backup channel if the area is prone to flooding
- runs parallel to the actual river
Benefits of flood relief channel
- removes chance of flooding
- new footpaths and cycle tracks
- calm water provides ideal areas for boating
- values of homes increase
- new habitats are created
Disadvantages of flood relief channel
- people living in the path of the relief channel have to be moved
- expensive £8 million on river exe
- long time to build 12 years on river exe
- in times of low flood it is unattractive
- water varies so habitats are unreliable
What is soft engineering ?
Soft engineering involves managing a river using natural materials and mimicking natural processes to protect more vulnerable areas
What is flood plain zoning ?
more permeable structures are built further away from the river, the area closest to the river are used for low-cost uses such as playing fields and pastures
What is flood warning?
- meteorological office analyse data from its 200 weather stations
- Environment agency provide updated flood alert information
- media publicise the information
- Environment agency provides information on how to prepare
What is River restoration?
When a river that has previously been hard engineered is restored to its natural channel
Benefits of river restoration
- increase biodiversity
- aesthetically pleasing
- reduces flooding
Disadvantages of river restoration
- expensive £1.2 million on lewisham
* not always effective as flood risk is the same as it was in the beginning
Benefits of planting trees
- reduce surface-runoff
- increase lag time
- creates new habitats
- more CO2 absorbed
- cheap
Disadvantages of planting trees
• loss of grazing
Where are trees planted to reduce flood risk
Across slopes and flood plains
Facts about river miles location, and area
- lowland area
- south east England
- runs under Gatwick airport
- 80km long
- catchment of 512cm2
Causes of flooding at the river mole
- geology
- rainfall
- urban growth
- blocked drains
- land use
How does the river moles geology cause floods?
- bedrock is mostly impermeable
- this causes high discharge
- increasing the chance of floods
How does the river moles rainfall cause flooding?
- rainfall during the 23-24 of December 2013 was the wettest in 35 years , yielding over 71mm
- 50mm fell in 24 hours
- if the ground is saturated surface-runoff increases when raining causing floods
How does urban growth near the river mole cause flooding ?
- expansion of Gatwick airport and Crawley has increased surface run-off by expanding impermeable surfaces
- removal of vegetation increases like time and surface run-off
How does land use cause flooding in the river mole?
- Industrial parks around the moles basin increases surface run-off
- lack of vegetation causes increase lag time and surface-run off
Impacts of the 23-24 December 2013 river mole flooding
- Gatwick airport power failure cause 100 delayed flights
- Power cuts left 100 homes in Merstham and Sidlow without power for 3 days
- 40 homes in Fetcham underwater throughout Christmas
- landslides in forking
- cars swept away
- damage to telephone lines in Brockham
Management of the river mole
- £15 million pounds was spent on the upper mole flood alleviation scheme
- built a dam wall at tilgate park
- flood ponds
- weirs and bank defences at molesy
- restored natural wetlands
- added meanders of vegetated banks to delay high discharge
How do you floodplains benefit and affect Gatwick airport?
- flood ponds were created around Gatwick airport runways to slow down the flow of water off hard surfaces so there is not a large peak discharge
- however the ponds attracted birds which is dangerous around planes also the ponds can be contaminated with oils from the runway
- however they aren’t going to put up netting
Economic issues with the river mole management
• very expensive it will cost £15 million
Social issues of the river moles management
- demand for houses causes homes to be built on floodplains increasing risk of flood as more impermeable surfaces
- chance of a second runway
Environmental issues of the river moles management
- runoff from runway contaminates the ponds as water contains oils
- bird flock to flood ponds which are dangerous to planes
