Rivers Flashcards
Describe the features of the middle course?6
- deeper as is being joined by multiple tributaries
- gradient is less steep
- less friction so the river has more power to erode
- river continues to erode vertically, but there is more lateral erosion as less gradient ( valley is flatter and with gentler slopes)
- increase in lateral erosion leads to meanders being formed
- erosion on the outside of meanders removes interlocking spurs and the valley thus becomes wider
Describe abrasion?
When load carried hits the beds and the banks
How can compacted or dry soil cause flooding?
This reduces the capacity for infiltration therefore increasing surface runoff
Water table
Current upper level of saturated rock/ soil where no more water can be absorbed
How is load affected downstream?
The mean particle size decreases with distance downstream
Describe how a river transports load via solution?(eg)
Soluble rocks will dissolve eg limestone and are carried in solution
Infiltration
Water sinking into soil/rock from the ground surface
disadvantage of dams and reservoirs?
Expensive to build Sediment is trapped behind the wall of the dam - erosion further downstream
Basin
An area drained by a river and all its tributaries
How does the channel roughness help the river to be more efficient in the lower course?3
Pebbles, stones and boulders in the beds and banks increase the roughness of the channel This increases friction and reduces the velocity of the river Channel roughness is higher in the upper course than further downstream
Features of a waterfall?
Steep drop Plunge pool White water Gorge V shaped
Describe attrition?
Reduction in size of the load itself as it knocks into other items of material
How much water can kielder water supply?
1,200,000 cubic meters
In a meander, describe the features of the outside bend?5
- deeper
- steeper
- a-symmetrical river channel
- larger bedload
- faster velocity
What does velocity of a river mean?
The rate of water movement
How can snowmelt cause flooding?
Fast runoff after winters or heavy snoefall
There is more time for erosion downstream, why does this mean the particle size decreases?3
- the major source of pebbles and stones in the river is from the rivers upper course - the further these rocks are carried downstream the more time there will have been for them to have been eroded by attrition and abrasion - abrasion and attrition makes rocks both smaller and rounder
Disadvantages of land use zonation?
Insurance premiums go up Deposition will occur (if eg a park is used as a zone) spoiling it Requires lots of free space
Explain the formation of a waterfall?
- hard rock underlain by soft rock
- the less resistant soft rock erodes faster (by hydraulic action and abrasion)
- resulting in undercutting occuring
- the overhang forms as under cutting countinues
- a plunge pool develops at the base
- the overhang eventually becomes too heavy and collapses into the plunge pool
- the plunge pool is then enlarged becaused of continued hydraulic action
How will a river transport soluble rocks?
Solution
What is the outside bend also know as?
River cliff
How can compacted or dry soil cause flooding?
This reduces the capacity for infiltration therefore increasing surface runoff
Describe solution?
When rock types such as limestone or chalk are dissolved by slightly acidic rainwater
Channel straightening?
Destroys natural habitats Spoils natural scenery Rivers will start to meander again so not permanent Expensive Will speed the river up, causing more erosion or flooding downstream
Physical causes of floods in Bangladesh?
Sea levels rising - there is no time for drainage and water comes at same time 10 degrees north equator so is prone to tropical cyclones 1.7 million km of flood plain Flat + low lying land (1/2 country is less than 10m above sea level) 3 major rivers which all flood
Source
A natural spring, the start of a river
What is the waters main loss of energy?2
Friction - 95%
What is the most important thing in determining a rivers velocity?
Efficiency / bed roughness are more important than gradient in determining velocity
what type of farming occurs in the middle course?
dairy farming, arable, crop farming
How can snowmelt cause flooding?
Fast runoff after winters or heavy snoefall
How can water be carried to different places in the UK?
Aqueducts and pipelines
Effects of Queensland floods?
- an area large than France + Germany was kept underwater - 100,000 homes had electricity cu off - mud + debris left - crops were damaged - loss for farmers
Disadvantage of channel deepening and widening?
Destroys natural habitat Hard engineering is expensive Material will be deposited on the river bed so not a permanent technique Only certain rivers have room to be widened
What is a levee?
Levées are raised banks that occur along the river and are made up of material that has been transported by the river.
List soft engendering methods?3
Afforestation (trees planted near to a river) - greater interception of rainwater and lower river discharge Flood warning systems - allows people time to evacuate and saves lives Land use zonation - putting less important land used in areas likely to be flooded, policies to control urban development - reduced damage
Describe the features of the lower course?6
- channel is wide and deep (wide valley floor)
- velocity is greatest as there is les friction
- river flows through a wide flat valley called a flood plain
- deposition of ALLUVIUM (sand and silt) because of karge load of eroded material
- still some lateral erosion
- very gentle gradient
How will a river transport smaller pebbles?
Saltation
Tributary
A stream that flows to a larger stream/other body of water
Describe how a river transports load via suspension?
Fine material is carrier within the water itself which is suspension
How does the shape of the channel help the river to be more efficient in the lower course?5
The river is deeper, wide and had a higher discharge Relatively less water is in contact with the wetted perimeter so friction from the bed and the banks is reduced
How might land use influence discharge?
Discharge is higher in unvegetated, urbanised and deforested basins because there is greater surface run off
Describe how a river transports load?
Large boulders traction - material is rolled along the bed Smaller pebbles - saltation - hopping motion Fine material - suspension - carried within the water itself Soluble rocks - dissolve eg limestone in solution
What are anomalies to particles decreasing with distance downstream?4
Influence of tributaries : stones and pebbles entering from a short tributary may be large and more angular than those in the main river Human activity : stones and pebbles can be added by people, e.g. Mining spoil can be large and angular
List hard water engendering methods?4
Channel straightening - water moves out of an area quicker Channel widening/ deepening - river can hold more water Channel course alteration - moving floodwaters away from settlements Dams and reservoirs - controls the release of water controlling flooding
In the upper course, what features can be found in river valleys?5
- vertical erosion DOMINANT PROCESS
- river channel narrow and shallow
- lined with large, angular bolders
- steep gradient
- low velocity because most of the energy is used to overcome friction with the rocky beds and banks of the river
How can bar flood defences cause flooding?
Lee es and dams can fail causing high river discharge and flooding
How many visitors per year go to kielder water?
300,000
How can a steep sided channel cause flooding?
A river channel surrounded by steep sided slopes cause fast surface runoff
List additional examples of anomalies to bradshaw’s model? ( discharge ) 3
Dames - decreases Urban areas - increases Vegetation - decreases
Mouth
Where a river empties into another body of water
Describe how a river transports load via traction?
- large boulders are transported via franc thin where material is rolled along the bed
Describe how a river transports its load?3
- Deposition off hrs when the amount of speed there is is reduced - The river thus has less energy - This can occur when there is a change in gradient
What landforms can be found in the lower course?4
Ox-bow lakes
Flood plains
leeves
deltas
Precipitation
Any source of moisture reaching the ground eg. River, snow
why don’t as many people live in the upper course?
- land is hard to build on
- area of high rainfall
How does extra water enter the river?4
From tributary streams, surface runoff, through flow and base flow
What is a hydrograph?2
Hydrograph a are graphs which show discharge ( the amount of water passing a particular point at a particular time )
Overland flow/ surface run off
Water flowing on top of the ground
Information on the Queensland floods?
- 36hrs non stop rain - amounting to 160mm - global warming increases intensity
How can bar flood defences cause flooding?
Lee es and dams can fail causing high river discharge and flooding
How does the shape of a river change downstream?6
- near the source the river valley starts in a V shape - it changes into a broad flat U in the middle - then becomes very wide near the mouth - it has steep sides at the start and a narrow valley floor with a river - further down the valleys sides are lower and gentler and have a wider floor - at the very end it is even wider and the river takes up only a part of the valley floor
Groundwater flow
Water stored in rock
Example of a reservoir?
Kielder water
What is the inside bend also known as?
Slip off slope
Through flow
Water flowing through the soil layer parallel to the surface
What landforms can be found in the upper course?
- V-shaped valleys
- Interlocking spurs
- Waterfalls
Human causes of floods in Bangladesh?
Increasing population (150 million ppl) houses built next to lakes so water can’t drain Deforestation increasing as people are desperate increase surface runoff Irrigation - more silt raises river beds with same discharge = flood Surface runoff increased by urbanisation ( concrete) less drainage Little infrastructure to take water away
Disadvantages of afforestation?
Requires a large area of land on a floodplain Less effective in winters if deciduous trees are used Takes a long time for trees to mature so is not an instant flood defence
How will a river transport large boulders?
By traction
What is discharge?
The volume of water flowing through a river channel at any given point
How might rock type and structure influence discharge?
The surface runoff component of discharge is lower in the drainage basins of permeable rock than impermeable rock
How might human influences influence discharge?2
Humans can either increase the discharge eg at a sewage outfall Or decrease the discharge eg abstraction of drinking water
Watershed
The boundary between 2 drains and basins
Disadvantages of flood warnings?
Can be inaccurate Does not save property farmland and businesses
How might tributaries influence discharge?
The increase in discharge when a tributary meets the main river depends on the size of the the tributary
Interception
Water prevented from reaching the surface by grass/trees
Describe how a river transports load via saltation?
Smaller pebbles are carried by saltation and move in a bouncing (hopping) motion
How can a steep sided channel cause flooding?
A river channel surrounded by steep sided slopes cause fast surface runoff
Describe how a river erodes?
Hydraulic action Abrasion Attrition Solution
What is load?
The total mass of material transported by the river
Case study of an MEDC river response?
Queensland floods - sand bags distributed - residents moved out - E v A. cricket match raised money for flood victims through their match fee - Nadal + Federer raised $70,000 in a charity match for flood victims
What are hydrographs measured in?
Cumecs ( cubic meters per second )
How will a river transport fine material?
Suspension
In a meander, describe the features of the inside bend of the river?5
- gentler, flatter
- smaller bedload
- deposition
- shallower
- slower velocity
Confluence
The junction of two or more rivers/streams
