Rivers Flashcards
What is the chain of stores in the hydrological cycle?
Interception storage - surface - soil storage - groundwater storage
What is the transfer from soil to groundwater?
Percolation
What is the flow from surface to the river channel?
Overland flow
What is the flow from interception to surface?
Throughfall stem flow
What is the flow from groundwater to the river?
Base flow
What is the transfer from surface to soil?
Infiltration
Define precipitation
Water in any form that falls from atmosphere to surface
Define evapotranspiration
Total amount of moisture removed by evaporation and transpiration from a vegetated land surface
Define run-off
All the water that enters a river and eventually flows out of the drainage basin
What are the inputs and outputs of the drainage basin?
Inputs: precipitation
Outputs: run-off and evapotranspiration
Define river discharge? And what unit does it take?
The volume of water passing a measuring point in a given time. Unit is ‘cumecs’
Define lag time
Delay between maximum rainfall and peak discharge
Define receding limb
Fall in discharge from the peak back to base level
Define peak discharge
Highest level of flow in the channel
Define rising limb
Rise in discharge from base level to peak discharge
Define base level
Level of flow in the channel without rainstorm effects
What urbanisation processes increase effects of storm
Building roads : more run-off as roads are permeable. Therefore, water cannot regulate or transfer through the normal systems
Straightening river channels: leads to faster delivery of water downstream
Building drains and sewers
Define erosion
The break-up of rocks by the action of rock particles being moved over the earth’s surface by water
Define transport
Movement of particles from where they were eroded to where they are deposited
Define deposition
The laying down of solid material, in the form of sediment, on the bed of a river
What factors determine a river’s total energy?
1) weight of the water
2) height of river above base level
3) steepness of channel
4) smoothness of wetted perimeter
What are the dominant processes in a high-energy river?
Erosion and transportation
What are the dominant processes in low-energy rivers?
Deposition
What are the four main erosional processes?
1) abrasion
2) hydraulic action
3) corrosion
4) attrition
What direction of erosion dominates in the upper course?
Vertical
What type of erosion dominated in the lower course?
Lateral
What is abrasion?
The scraping action of the river load acts to wear away the river banks and bed
What is hydraulic action?
The movement of unconsolidated material due to frictional drag of moving water
(Particularly good at removing the banks from meanders)
What is Corrosion?
Where rocks are dissolved by weak acids in river water.
This is most effective on rocks that contain carbonates
What is attrition?
The reduction in the size of fragments and particles in a river as a result of sediment bumping into one another
It takes energy for a river to transport its load. What other processes expend a river’s energy at the same time as transportation?
Erosion and friction
What are the two main sources of the sediment that makes up a river’s load?
Material washed and fallen into river from valley sides
Material eroded itself from banks and the bed
Identify four main types of river transport. Provide a very short definition of each.
Traction
Saltation
Suspension
Solution
Define capacity
The measure of the amount of material it can carry
Define competence
The diameter of the largest particle it can carry for a given velocity
If the velocity of a river triples, by how many times will its competence increase?
A river’s competence increases according to the sixth power of its velocity
From small to big: what is the offer of sediment?
Clay - silt - sand - gravel - coarser material
Why are small silt/clay particles more difficult to transport than sand?
They are hard to pick up (entrain) because they tend to stick together
Why are large particles deposited soon after being swept up in a flow?
There is a small difference between critical erosion velocity and settling velocity for the larger particles
What do particles get smaller the further downstream the river travels?
Attrition
Average velocity is highest here and therefore able to transport more material
Define the long profile
Illustrates the changes in the altitude of the course of the river from its source, along the entire length of its channel, to the river mouth.
Define the cross profile
View of the valley from one side to another
Describe the valley shale in the upper course
V shaped , steep sides narrow bottom. With interlocking spurs.
Describe the valley shape in the middle course
Wide flood plain where valley sides are steadily lowered
Describe the valley shape in the lower course
A wide flood plain with:
- levées
- oxbow lakes
- bluffs
What does a graded profile represent?
It shows the long profile after the irregularities are worn away by erosion. It’s ‘smooth’
What determines the potential energy of a river at a given point?
Fixed by the altitude of the source of the stream in relation to base level
What determines the kinetic energy of a river at a given point?
Generated by the flow of the river which converts potential energy into moving energy. It is determined by volume of flowing water.
Explain formation of river terraces
Rejuvenation -base level change (isostatic)
River erodes vertically into former flood plain to produce features called river terraces
Remnant of a former flood plain left at a higher level after rejuvenation
When a river renews its downcutting power, it sinks its channel leaving former floodplain above
If vertical erosion is rapid, what kind of terrace does it leave?
Paired terraces
If vertical erosion is slower, what kind of terraces does it leave?
Unpaired terraces as river meanders
Describe and explain an incised meander
They are particularly well developed
River’s base level falls, vertical erosion (due to rate it occurs)
Results in becoming incised or deepened
describe entrenched meanders
They are symmetrical
They form when a river down cuts quickly
Therefore, little opportunity for lateral erosion
The vertical erosion leaves steep sides and a “gorge-like” appearance
Ingrown meanders
These are asymmetrical
Form when a river downcuts less rapidly
River can then downcut laterally and vertically
Steeper cliffs in our bends and gentle cliffs on inner bends
Formation of potholes
Where depressions exist in the channel floor, turbulent flow can cause pebbles to spin around and erode hollows through abrasion
Above river level (circular, round, oval)
Upper course - high GPE so sediment erodes downwards
Created during hugh stages of discharge
Original potholes join together through further erosion= bigger potholes
As holes get bigger, even bigger debris can become trapped in the pothole
Formation of braided channels
Occurs in river’s where discharge rapidly fluctuates
Where the river is split into several channels
Features of river’s that have large loads of sand and gravel
Banks formed are generally unstable and easily eroded
As a result river comes very wide and not so deep
River can become choked - sandbars
Formation of levées
Middle and lower courses
River is at risk from flooding during times of high discharge
If it floods the velocity of water falls as it goes over bank
Results in deposition (decrease in competence)
Coarse material deposited first
Subsequent floods increase the size of the banks
Formation of deltas
Form when rate of deposition exceeds rate of sediment removal
They are a feature of deposition
Located at mouth of river
Occurs where velocity decreases and sediment increases
Bedload and suspended material dumped
Flocculation - Clay - Settles
What is a meandering river?
Large, sweeping curves in a river’s middle and lower stages
How do meanders form?
Form where alternating POOLS (deep) and RIFFLES (shallow) develop at equally spaced intervals
The spacing and distance between riffles and pools causes the river’s flow to become uneven and maximum flow to be concentrated one one side of the river
Turbulence increases in and around pools and the water speeds up, so the flow begins to twist and coil. Thalweg
This causes corkscrew-like currents in the river called helicoidal flow, which spiral from bank to bank between pools
This causes more erosion and feeling of the pools. Also, it causes eroded material to be deposited on the inside of the next bend, where river loses energy
What are the human causes of floods?
Urbanisation
• often built on flood plains, susceptible to flooding
• tarmac = permeable
Deforestation
• increased soil erosion
• loss of interception
(REDUCED LAG TIME)
Physical causes of floods
High levels of precipitation over a short period of time
Melting of snow
Lack of vegetation cover
Climatic hazards
When do flood’s occur ?
Where a river’s discharge exceeds the capacity of its channel to carry that discharge
What were the conditions in York before the flood ?
Upper course very steep
Seams of permeable limestone
Arable farming in upland areas means there is no interception
New housing areas and out of town shopping areas
What were the conditions in Bangladesh?
Confluence of 3 river’s (Meghna, Ganges, Brahmaputra)
Snow melt from the Himalayas
Low-lying country
Cyclones
Deforestation
Urbanisation
What were the impacts of flooding in York?
500 homes inundated
250 evacuated from homes
300 year old bridge closed
Gas leak
Phone signal problems
Road closures
What was the response in York?
10,000 sandbags used
600 military personnel
125 mountain rescue members
Countless volunteers
14,000 joined a Facebook group offering help
Facilities like sports centres offered accommodation
Nestlé donated £100,000
£1 million donated in one month
What were the impacts in Bangladesh?
Death toll: more than 800
Homeless: 36 million out of a possible 125 million
Dhaka alone: 100,000 displaced
Dirty floodwater
15,000 km road destroyed
900 bridges destroyed
$7 billion damages
38% land area flooded
What was the response in Bangladesh?
Infrastructure issues meant that help couldn’t get to rural areas quick enough
Foreign aid: rice, clothing, medicines (21 million from U.K.)
Water purification tablets provided
Dhaka integrated flood protection project •radio to issue warnings •cluster villages •embankments created •sluice gates •slope protection
Factors that influence the storm hydrograph
Human: Urban land use Flood defences Deforestation Agricultural land use
Physical: Intensity of rainfall Antecedent soil moisture Steepness of slopes Rock type Permeability of soil Vegetation
Drainage basin
DB/Catchment area is an area that is drained by a river and its tributaries.
Water shed splits drainage basins
Flood management - Taunton
Flood alleviation scheme
River Tone constructed in 1960’s
The defences comprise of: •raised walls • green corridor by French weird • technocentric bridge • channelisation • river wall - increase bank full capacity • embankment created
Flood management in York (river Ouse)
Soft engineering vs. Hard engineering vs. Integrated management
There has been an attempt to manage this river holistically
- afforestation (reduce flashy response)
- flood warnings (latest technology)
- Clifton kings washlands - takes up excess capacity water with sluice gates
- The Foss Barrier - 8 pumps capable of 30 tonnes water/second
Key words
Alleviation
Mitigation
Oil patterns
•Production: Saudi Arabia 9.7 bbl/day
High producers and use own resources
Majority produced in Middle East, USA and Russia
•Consumption: USA close to 21 bbl/day (most by four-fold
China-Japan-Germany-Russia
High consumption usually occurs in developed or highly populated areas
•Trade: Brazil to USA and China more than 1 million b/day
Nigeria and Algeria export a lot
Saudi Arabia greatest distributor
Gas patterns
•Production: North America has the largest production of gas (29 trillion cubic feet)
Russia+Middle East around 26 trillion cubic feet
•Consumption:
N.America, Europe and Asia high consumers
There has been an increase in consumption because: increase pop. , better technology, increase in demand and decrease in other energy resources
What are TNC’s?
TNC is one that operates in at least two countries
Centres of production in one part of the world and HQ in another. Therefore, TNC’s tend to be hierarchical
In 2007, 6 out of ten largest TNC’s were oil companies
8 different functions of a TNC (BP example)
Exploration Drilling Extraction Transport Storage Refining (manufacturing) Distribution and sales Training and workforce
Facts about BP
84,000 employees
Annual income of €360 billion
17,000 retail sites
Exploration and extraction in BP
How many countries is BP active?
Which ones?
How many barrels a day?
2005: active in 26 countries
Incl. Angola/Azerbaijan and Gulf of Mexico
4 billion barrels a day
What is production?
The process of drilling and extracting
