Physical- Rivers Flashcards
What is the hydrological cycle?
The circulatory system by which water is transferred between oceans and landmasses.
What is the drainage basin?
The area of land (catchment area) from which a river system obtains its supply of water.
What is river discharge?
The amount of water flowing in a river, measured in cumecs.
What is the river regime?
The annual pattern of the discharge of a river responding to the regions climate.
What is the velocity?
The speed of a rivers velocity.
What is the long profile?
A cross-section of a river from its source to its mouth.
What is a estuary?
Area of lower river or mouth which is affected by tidal change.
What is evapotranspiration?
The total amount of moisture lost by evaporation and transpiration from a vegetated land surface.
What is infiltration?
Water soaking into the soil.
What is interception?
Raindrops are prevented from falling directly onto the soil surface by vegetation.
What is percolation?
Water seeping down through the soil into the groundwater store
What is throughfall?
Water dripping from one leaf to another.
What is Stemflow?
Water running down plant stems and branches.
What is throughflow?
Water moving slowly downhill through the soil.
What is groundwater flow?
Water flowing slowly below the water table through permeable rock.
What is channel flow?
Water flowing along the river itself.
Give the five types of river storage
Interception Vegetation storage Surface storage Groundwater storage Channel storage
What is vegetation storage?
Water taken up by plants
What is surface storage?
Puddles, ponds and lakes
What is groundwater storage?
Water collected underground in pore spaces in rock and soil. The top underground area that is saturated is the water table
What is channel storage?
Rivers, streams
What is an isolated system?
Nothing enters/leaves.
What is a closed system?
Inputs and outputs of energy but not matter e.g. Earth
What is an open system?
Inputs and outputs of both energy and matter e.g. Living things- river
What is equilibrium?
The volume of the liquid stays the same as does its state and energy.
What is steady state equilibrium?
No overall change in the store of energy and matter.
What is dynamic equilibrium?
A system that is balanced but is constantly changing e.g. erosion. It is a sate of stability that changes through time. e.g. river
What is the hydrological cycle an example of?
A closed system.
Give two inputs into the hydrological cycle?
Geothermal energy
Short wave radiations of heat and light.
Give 5 stores in the hydrological cycle?
Ice and Snow Lakes Groundwater Atmosphere Oceans and Seas
Give 4 transfers in the hydrological cycle?
Precipitation
Advection
Rivers
Evaporation
What is the output in the hydrological cycle?
Heat, light and sound.
What is a hydrograph?
A graph which shows variations in river discharge over a particular period of time and shows the response of a drainage basin and over a year may be called its river regime.
What is a flood hydrograph?
A graph showing how the discharge of a river at a particular point responded to a specific rainfall event.
What is the peak discharge?
The maximum flow of the river often in response to rainfall.
What is lag time?
The length of time between peak precipitation and peak discharge.
What is the rising limb?
The rapid increase in river discharge due to overland flow and throughflow.
What is the falling limb?
The fall in river discharge due to the decline of overland flow and throughflow.
What is baseflow?
The normal discharge for a discharge which reflects seasonal changes. It is part of the river’s discharge that is produced by groundwater seeping slowly into the river bed.
What is peak precipitation?
Highest amount of precipitation at a certain time.
What is river discharge?
The volume of flow of water passing a gauging station in a river at a particular time.
What is discharge measured in?
cumecs m3/s
What is velocity of water measured in?
meters/ second (m/s-1)
What is the measurement for the cross sectional area of a river?
m2
What does Q stand for?
Discharge
What does V stand for?
Velocity of water
What does A stand for?
Cross sectional area of a river.
What is the formula for calculating discharge?
Q= VxA
Name the factors which affect discharge?
1) Basin size, shape and relief
2) Precipitation
3) Temperature
4) Land use
5) Geology
6) Soil type
7) Drainage basin
8) Tides and storm surges
How does the basin size affect discharge?
Small… Rainfall reaches channel quickly, so lag time will be short and the hydrograph will rise rapidly.
Large…
How does the basin shape affect discharge?
Circular… Shorter lag time and higher peak flow because the points on the watershed are equidistant from the gauging station.
Elongated…
How does prolonged rainfall affect the hydrograph?
Flooding often occurs following a long period of rainfall and the ground has become saturated and infiltration has been replaced by surface run-off. The effect on the hydrograph will be over a period of time.
How do intense storms affect river discharge and the hydrograph?
When heavy rainfall occurs, the rainfall intensity may be greater than the storage capacity of the soil. As a result, surface runoff is likely to produce rapid rises (flash floods)
Give an example of an intense storm?
Convectional thunderstorms
How does snowfall affect the river discharge and the hydrograph?
Heavy snowfall means that water is held in storage and the river levels drop. When temperatures rise rapidly, meltwater soon reaches the river and if the ground is frozen infiltration will be impeded. If melting occurs over a longer period the response will be more subdued.
How does temperature affect river discharge and hydrographs?
Extremes of temperature restrict infiltration and increase surface runoff. If evapotranspiration rates are high, then there will be less water available to flow into the main river.
Land use
Come BACK LATER!
What is a porous rock?
A rock which contains numerous pores which can be stored with water e.g. sandstone or chalk
What is pervious rock?
Pervious rock allows water to flow along bedding planes and down joints within the rock, although the rock itself is impervious
Give an example of a pervious rock?
Carboniferous Limestone
What are the two types of permeable rock?
Porous and pervious
What is the effect of impermeable rock on discharge?
Impermeable rocks e.g. granite do not allow water to pass through them so there is more surface run-off and a higher discharge
How does the soil type affect river discharge?
Soil type controls the speed of infiltration, amount of soil moisture storage and the rate of throughflow.
What is the effect of sandy soils on river discharge?
Sandy soils have large pore spaces and allow rapid infiltration preventing flooding.
What is the effect of clay soils on river discharge?
Clay has much smaller pore spaces which reduces infiltration and throughflow, but encourages surface runoff and increases the risk of flooding.
How does the drainage density affect the discharge?
This refers to the number of surface streams in a given area. The density is higher on impermeable rocks and lower on permeable ones. A higher density means a greater chance of flash flooding.
How is a flash flood shown on a hydrograph?
Shorter lag time and a higher peak flow in relation to normal discharge.
How do tides and storm surges affect discharge?
High spring tides prevent river flood from escaping to the sea and water therefore builds up. If high tide coincides with gale force winds, the result may be a storm surge.
Give an example of a storm surge?
South-East England in 1953 prompting the construction of the Thames Barrier
Name the 4 physical characteristics of the drainage basin which affect discharge?
- Basin size
- Basin shape
- Basin density
- Rock type
Name the 4 meteorological characteristics which affect discharge?
- Rainfall amount
- Rainfall duration
- Type of precipitation
- Soil moisture levels
What are the human characteristics which affect river discharge?
- River use- Industrial/ domestic
- Land use- Rural/ urban
- Surface water stores
How does limited vegetation cover affect discharge?
1) Less rainfall interception
2) Low transpiration rates
3) Throughflow unimpeded by the shallow roots
4) Little impact on surface runoff
5) Higher discharge likely.
How does a greater use of the river affect discharge?
Industrial extraction/ Irrigation/ Domestic water supply extraction reduce water volume lowering the discharge
How does urbanisation affect the river discharge?
1) Increased impermeable surfaces and drains increase surface runoff.
2) Less vegetation means less interception
3) Higher discharge likely
What are the characteristics of a flashy hydrograph?
- Steep rising limb
- High peak discharge
What are the characteristics of a subdued hydrograph?
Gentle rising limb
Long lag time
What is a river regime?
A hydrograph showing the years worth of discharge
What is a rivers long profile directly related to?
Potential energy and kinetic energy
What is potential energy?
Stored energy fixed by the altitude of the source of the stream in relation to base level
What is kinetic energy?
Energy due to movement , and is generated by the flow of the river which converts PE into movement.
What affects the amount of kinetic energy a river has?
- Discharge
- Channel gradient
- Average velocity
What is competence?
- The maximum size of particles that a river can transport
- When velocity and energy levels are low the river can only transport smaller particles e.g. clay and silt.
- When river levels are high, rivers can transport larger particles e.g. pebbles and boulders
What is capacity?
- The total load (material) that the river actually transports at a particular discharge or energy level.
- The capacity increases as the discharge increases.
- The river is capable of carrying more sediment
Description of the upper course…
- V shaped
- Channel profile is approximately 1.5m across
- Interlocking spurs
Describe the middle course…
U shaped valley
Channel profile 5m
Describe the lower course…
Wide and deep
20m across
Processes in the upper course…
- Weathering
- Vertical erosion
- Headward erosion
Processes in the middle course…
- Lateral erosion
- Transportation
Processes in the lower course…
Deposition- flooding
Transportation
Landforms in the upper course…
Rapids
Waterfalls and gorges
Landforms in the middle course…
Meanders
Landforms in the lower course…
Levee
Ox-bow lakes
Delta
Braided channel
Why do rivers flow downhill?
Gravity
What is the diagrammatic representation of a river channel known as?
The long profile
What shape is the long profile?
Concave
What is erosion?
The breakdown and removal of the river bed and banks
What is vertical erosion?
Downwards erosion found in the upper course where rivers have large angular bedload.
What is headward erosion?
Most common at the source and in the formation of gorges.
What is lateral erosion?
Dominate in the middle course where rivers meander from side to side.
What is abrasion?
1) River picks up material and rubs it along the beds and banks.
What is attrition?
1) As bed load moves downstream, boulders collide with other material making the load smoother and rounder.
What is hydraulic action?
1) Force of the water
What is solution/corrosion?
Rocks dissolve due to the acidity of the water e.g. Limestone and chalk
What is the Bradshaw model?
Diagram showing how the river changes as it moves downstream
What is traction?
Large particles such as pebbles and boulders are rolled along the river bed.
What is solution?
- Dissolved minerals carried in the body of the water e.g. Calcium and Sodium
- Particles are invisible
What is saltation?
Large particles like gravel are bounced along the river bed.
What is suspension?
- Smaller particles such as silt, clay or fine sand are carried along in the body of the water without making contact with the beds or banks.
How does deposition occur?
1) Velocity decreases
2) Less energy
3) Doesn’t have competence or capacity to carry all its load.
4) Heaviest material deposited first
Things which cause deposition…
- Delta
- Flooding
- Levee
- Snow
What is the Hjulstrom diagram?
A diagram showing the relationship between erosion, transportation and deposition.
Why do silt and clay need higher velocities than their sizes would suggest?
In winter particles stick together due to electromagnetic forces meaning they are heavier and require a higher velocity to move them (flocculation).
What is the rivers power?
The energy available to overcome friction and move sediment.
What is equilibrium?
When the river has just enough energy to transport the sediment available.
What happens if the river has more energy than it needs to transport its load?
Erosion
What happens if there is less energy than the load requires?
Deposition
Competence and capacity?
Competence is size of the load.
Capacity is amount of load that the river can actually carry.
Why does discharge increase downstream?
1) River widens and deepens
2) Capacity increases
3) Tributaries
4) Increased velocity
Why does channel width increases downstream?
1) Lateral erosion
2) Potential energy- kinetic energy
3) Tributaries
4) Velocity
Why does channel depth increase with distance downstream?
1) Tributaries
2) Velocity
3) Vertical erosion
Why does velocity increase downstream?
1) Potential energy- kinetic energy
Why does the load quantity increase downstream?
1) More velocity
2) Energy
3) Capacity
Why does the load particle size decrease over time?
1) More energy=more erosion
Why does channel bed roughness decrease downstream?
1) Smoother and rounder rocks-erosion
2) Efficiency increased
Why does the gradient decrease downstream?
1) River meanders across land rather than erode it.
For the river to transport silt and clay, why does it need a higher velocity than the size of the particles would suggest?
- Particles stick together due to electromagnetic forces meaning they are heavier and require a higher velocity to move them- FLOCEULATION
Once set in motion, fine particles can be transported even if the velocity is…
… very low
Large coarse particles are deposited…
Rapidly as velocity falls
In channels with mainly boulders and gravel transport occurs…
Only at high flows
What is the velocity called when a sediment drops to the channel bed?
The settling velocity
How is energy lost within a river?
Internal friction due to the turbulence of the river itself.
What is the cross-sectional area?
Calculated by width x mean depth
Area of water
What is the wetted perimeter?
The perimeter of a rivers channel cross-section that is in contact with the water.
What is the hydraulic radius?
The ratio of the cross-sectional area of the channel and the length of its wetted perimeter.
Calculated by Area/ wetted perimeter
What is the result of a larger hydraulic radius?
There is less water in contact with the beds and banks therefore there is less frictional drag and a higher velocity.
What is the result of a smaller hydraulic radius?
More water in contact with the beds and banks results in more frictional drag and a lower velocity.
What is the river like during the winter?
Bank Full
How are potholes formed?
1) Formed when a small hollow or depression is created and pebbles or rocks become trapped inside them.
2) Material is swirled around the hole causing it to become larger due to abrasion- pothole drilling.
3) Hydraulic action and the force of the water also contribute to increase in size.
4) Over time, they may join together to create sudden drops in the channel gradient.
Describe LESS for Potholes
L- Bedrock of a river
E- Upper course, Afon Glaslyn River
S- 1cm-2m diameter
S- Smooth and rounded
Describe LESS for rapids?
L- Sudden increase in channel gradient
E- Aysgarth Falls, Yorkshire- 30m- 1 mile
S- 1-2m in height, several hundred in length
S- Series of small waterfalls
Describe the formation of rapids?
1) Small terraces of water 1-2m in height
2) Alternating hard and soft rock, occur when stream stream flow is restricted which increases the velocity of the water.
3) As water flows over boulders, the river can flow back on itself in the form of underwater currents and HA forms some deeper pools.
4) Turbulent flow also creates eddy currents in sheltered areas away from the main river channel.
5) Water depth is shallow near rock lips where velocity is fastest with deep pools below the resistant rock ledges.
Describe the formation of a waterfall and gorge?
1) Top section is made from a hard rock called Whinstone but underneath is a soft rock called carboniferous limestone. This is undercut as it erodes faster leaving an overhang at the top.
2) Plunge pool deepened over time by HA and abrasion
3) The continuous undercutting results in the collapse of the whinstone overhang.
4) Over time the process is repeated but because of headward erosion gradually retreats further upstream leaving a narrow, deep gorge in front of it.
5) Durham gorge 700m
Describe LESS for a waterfall
L- Upper course, Durham
E- High Force, River Tee
S- 21m high, gorge 700m
Describe the formation of a meander…
1) Periods of high discharge= greater capacity and competence meaning more material is eroded and transported
2) Discharge decreases, material deposited, river develops a sequence of deep pools and shallow riffles
3) Water flows inefficiently over riffles, HR decreases as there is a high amount of friction which slows the river down.
4) To avoid areas of higher frictional contact the river goes around them.
5) The water becomes deeper as the HR is higher so there is less friction, increasing the speed, giving greater erosive power and forming pools.
Describe the formation of a meander at high flow…
6) At high flow the water flowing around the riffle will be propelled by centripetal force directing maximum velocity at one bank, resulting in undercutting due to abrasion and HA.
7) Outer, concave bank, which having been undercut forms a river cliff. At the same time deposition occurs on inside, convex bank where the water is slowest. This forms a slip-off slope giving an asymmetrical channel slope and causing the thalweg to move to the outside of the bend.
8) Doesn’t become wider because erosion and deposition occur simultaneously but the sinuosity of the bend increases
9) Corkscrew like motion of water is known as the helicoidal flow.
10) Eroded material transported downstream, and deposited on the slip off slope on the inside of the next meander bend.
Give LESS for meanders?
L- Middle/lower course e.g. Snowdonia
E- Afon Glaslyn
S- Asymmetrical channel
S- Sinuous
Describe the formation of levees?
1) River floods and water spills onto the floodplain increasing wetted perimeter.
2) Consequently, HR decreases as the river is less efficient due to friction.
3) Heavier sediment is deposited close to the channel; finer material further away.
4) During a dry spell, river slows and deposits material on the bed.
5) After many floods and dry spells, material builds up while also raising the river bed. Subsequently, the river can flow above the floodplain as it is contained by the levees.
LESS for levees
L- Floodplains
E- Mississippi river
S- 3,200Km and up to 15m high with an average of 7m
S- Raised parallel banks
How is a delta formed?
1) River loses energy as it meets a area of slow-moving water e.g. the sea
2) The combination of fresh and salt water result in an electric charge which cause clay particles to coagulate and settle on the seabed, a process known as flocculation.
3) Deposits are laid on the sea bed in a three-fold sequence- Heaviest first on the topset beds, medium on the forest beds and finest on the bottomsets last.
What are the three types of delta?
Arcurate… Nile, Egypt
Cuspate… Tiber, Italy
Birds foot… Mississippi, USA
Describe the formation of channel braiding?
1) During periods of high discharge the river erodes easily
2) Sediment from banks is transported downstream due to high competence and capacity.
3) Water levels fall and energy decreases, coarsest material is deposited and begins to block the river channel.
4) Doesn’t have the competence to move it so the channel subdivides into a series of smaller and diverging channels, seeking the easiest route past obstruction.
Describe channel braiding LESS
L- Rivers with high sediment and a variable discharge
E- Afon Glaslyn river- 5Km before it reaches the sea
S- Wide in relation to depth
S- Split into several channels by islands of sediment
What is a floodplain?
Wide, flat area of land surrounding a river in its lower course e.g. Afon Glaslyn river
Describe the formation of a floodplain?
1) Erosion and decomposition. Meanders laterally erode and widen the floodplain. The width of the floodplain is determined by the amount of meander migration and lateral erosion occurring.
2) Decomposition on the slip-off slopes provide sediment to build up valley floor and this is added to during flooding when the river overflows.
3) River carries its load and as water spills onto floodplain there is lots of friction because of the large wetted perimeter and the water being shallow. As a result, velocity decreases and the river deposits.
4) Over thousands of years these deposits build up.
What is rejuvenation?
When there is either a fall in sea level relative to the level of the land (fall in base level) or a rise of the land relative to the sea. This causes an increase in the rivers potential energy.
What 2 factors can cause base level to change?
1) Sea level could fall due to climate change e.g. in a glacial period more water will be stored as ice and sea levels will lower- EUSTATIC
2) The land could rise up due to glacial rebound- Isostatic change
What are the landforms created by rejuvenation?
1) Knick point
2) River terraces
3) Incised meanders
Describe the formation of a knick point?
1) The drop in base level gives the river greater potential energy, increasing its vertical erosion potential
2) The long profile of the river is extended and a knick point will form marking the junction between the original long profile and the new one.
3) Adjustments to the new base level start at the sea and gradually work their way up the rivers course. As the river is eroding it will erode the knick point gradually and it will recede upstream.
4) The rate at which it erodes depends on the resistance of the rock.
What is a knick point?
A sudden break or irregularity in the gradient along the long profile of a river.
What is a river terrace?
A narrow, flat piece of ground that runs parallel to the river on either side, above the level of the floodplain.
Describe the formation of river terraces?
1) As the water level drops relative to the land the river’s capacity to erode increases and it begins to erode vertically leaving the old floodplain above the present level of the river.
2) Lateral erosion also occurs and widens the new valley.
3) It rejuvenation takes place again the process is repeated and a new pair of terraces is formed beneath the original.
What is an incised meander?
A meander that has deeply cut into the floodplain, creating steep cliff like banks.
How is an incised meander formed?
1) As the water level drops relative to the land the river’s capacity to erode increases and it begins to erode vertically- the meander becomes deepened/incised
2) When incision is slow, lateral erosion is dominant and an ingrown meander may be produced- valley becomes asymmetrical, with steep cliffs on the outer bend and more gentle slip off slopes on the inner bend.
3) When incision is rapid, vertical erosion dominates- valley becomes more symmetrical with steep sides and a gorge like appearance, these are described as entrenched meanders.
What are the physical causes of flooding?
1) Excessive or intense precipitation
2) Snowmelt
3) Climatic hazards
4) Relief
5) Vegetation
6) Soil type and depth
7) Geology
8) Drainage density
What are the human causes of flooding?
1) Urbanisation
2) Forestation
3) River management
4) Climate change
How can climatic hazards cause flooding?
- Cyclones and hurricanes and low pressure systems lead to increased precipitation.
How does the relief of the land lead to flooding?
- Steeper slopes mean less water can infiltrate the soil resulting in increased runoff which decreases the lag-time and leads to river exceeding bank full.
What does greater vegetation mean for flooding?
- Interception, storage and evapotranspiration
How does soil type and depth cause flooding?
- Clay soils retain a greater amount of water, thus becoming saturated more quickly than free-draining sandy soil
- Deeper soil absorbs more water and results in less runoff
How does geology cause flooding?
- Impermeable rock impedes percolation and ground storage, and results in soils becoming saturated more quickly.
How does the drainage density cause flooding?
- When drainage density is high there is a shorter lag-time and an increased risk of flooding and the hydrograph is flashy and bank full may be exceeded.
How does urbanisation lead to flooding?
- Construction on floodplains
- Impermeable surfaces
- Removal of vegetated surfaces
- Drains and sewer channels increase discharge
How does deforestation increase flooding?
- Soil erosion
- Sediment finds its way into the river, blocking it
- Decreases interception and evapotranspiration
How does river management increase flooding?
- Embankments can prevent floodwater returning to the river
- Inappropriate use of floodgates on dams, flooding downstream
- Levees may be breached
River straightening increases flooding downstream
How does climate change increase climate change?
- Increasing sea temperatures leads to greater frequency and severity of tropical storms.
- Increased temperatures result in greater evaporation and rainfall.
- Rise in sea levels
Define magnitude
- The size of the flood often measured in disacharge
Define frequency
The number of times you would expect to see a flood of a given magnitude.
What is the case study for flooding in an MEDC?
Sheffield floods 2007
What were the physical causes of flooding in Sheffield 2007?
- Heavy and prolonged rainfall
- 1 in 200 year flood
- Intense depressions due to a stronger than normal jet stream
- 285mm in June
- 25th June- 100mm in 24 hours
- s fast-flowing rivers
What were the human causes of the Sheffield 2007 floods?
- Construction on floodplain
- Insufficient drainage and impermeable surfaces- 5% damage from surface water
- Culverts built- failed
- Failure of flood defences- wall collapse of river Don
What were the effects of the Sheffield 2007 floods?
- Crack in dam wall at Ulley reservoir
- 95% flooding= direct fluvial flooding
- 1400 residential properties flooded
- Railway station and 41 road closures
- 2 dead
- Meadowhall and Hillsborough stadium flooded
- 1000 businesses affected
- £15 million for roads
What were the short term management strategies for the Sheffield floods?
- MET office warnings
- Ulley reservoir- firemen to lower water level, 700 evacuated, part of M1 closed
- 20,000 sandbags prepared
- RAF helicopters for rescue
- Emergency aid from government to help with clear-up
- All gullies cleared once a year by council.
What were the long term management strategies of the Sheffield floods?
- Review of flood management strategies
- Environmental agency spent £4 million on flood prevention from 2007-10 in Sheffield.
- SCC must work with EA by not allowing development in high risk areas.
- Over 200 businesses balloted for a £1.4 million improvement in flood defences.
What is hard engineering?
The construction of artificial structures that through science, technology and force prevent a river from flooding- work against nature
What is soft engineering?
Use natural resources and local people’s knowledge of the river to reduce the risk posed by a flood- work with nature.
What are the general advantages of hard engineering?
1) Large impact on the river
2) Vital for cities such as London protected by the Thames flood barrier.
What are the general disadvantages of hard engineering?
1) Disrupt ecological systems in the drainage basin.
2) Failure would be catastrophic
3) High cost, technological requirements and maintenance
4) Rare in LEDCs
What are the general advantages of soft engineering?
1) Reduce impact of flooding
2) Significantly cheaper
3) Suitable for developing countries
4) Lower education and technology requirements so can be implemented by local people.
5) More sustainable
6) Don’t disturb natural processes and ecological systems
What is a dam?
A giant wall built across a channel to impede its flow. Water builds up behind the dam and forms a reservoir which can then be controlled. This helps keep discharge downstream of the dam low even during prolonged heavy rainfall.
What are the advantages of a dam?
1) Controls discharge
2) Generates HEP
3) Reservoir water supply
4) Recreational activities
5) Prevents flooding downstream
6) Irrigation for farmland.
What are the disadvantages of dams?
1) Huge amount of flooding which destroys habitats, displaces people and prevents fish migrating.
2) Expensive to build and maintain.
3) Terrorist target
What is an artificial levee (embankment)?
- An artificial version of their natural counterparts
- Extend the channel’s height and increases its bankfull discharge
- Concrete resistant to erosion
What is an example of a dam?
Three Gorges dam
What is an example of a artificial levee?
Mississippi River
What are the advantages of artificial levees?
- Allows development of floodplain
- Larger than normal levees and resistant to erosion
What are the disadvantages of artificial levees?
- Expensive
- If water overflows flooding can be worse
- Constant maintenance
- Sedimentation reduces capacity
What is channel straightening (channelisation)?
- Blocks off meanders and constructs alternate, straighter routes allowing the river to flow faster preventing pooling and reducing risk of flooding.
Give an example of channelisation?
Mississippi river
What are the advantages of channelisation?
- Provide alternative route increases efficiency
- Reduce risk of flooding
- Aids navigation (transport)
- Habitats may survive
- Allows the control of where the river goes
What are the disadvantages of channelisation?
- Expensive
- Unnatural
- Destruction of habitats
- Flooding risk downstream
What is a diversion spillway?
- Artificial channels that a river can flow into when its discharge rises.
- Channels move water around and either send it back into the river downstream or another river.
- Generally have floodgates on them that can be used to control the volume of water in the spillway.
Give an example of a diversion spillway?
Windsor area on Thames
What are the advantages of a diversion spillway?
- Alternate route
- Straighter and shorter
- Reduces flood risk
What are the disadvantages of diversion spillways?
- Habitats completely destroyed
- Expensive
- Flood gates maintained
- Flooding downstream
- If the spillway failed it could cause widespread damage
What is floodplain zoning?
- Placing restrictions on land usage on areas surrounding the river.
- Construction is unlimited outside the floodplain but the floodplain itself is linked to outdoor facilities like playing fields and parks.
What are the advantages of floodplain zoning?
- Reduces damage when the river floods
- Floodplain isn’t urbanised so infiltration can occur and surface runoff is reduced.
What are the disadvantages of floodplain zoning?
- Limits development to certain areas
- If floodplain is already developed then this is ineffective
What is an example of floodplain zoning?
A61 River Donne
What is afforestation?
- Planting trees to increase interception and reduce through flow.
What are the advantages of afforestation?
- New habitats
- Very effective when combined with floodplain zoning
- Prevents soil erosion reducing the amount of soil entering the river and keeping capacity high
- Cheap
What are the disadvantages of afforestation?
- Requires a large amount of space
- Unpopular among farmers as trees use nutrients from the soil.
- Takes 40 years for trees to grow.
Give an example of afforestation?
Pickering, North Yorkshire
What is river restoration?
- Restoring a river that has undergone hard engineering back to its original course.
- Used when land is no longer valuable, and can help reduce teh risk of flooding in other areas.
What is an example of river restoration?
London
What are the advantages of river restoration?
- Prevents and reverts environmental and ecological damage introduced by hard engineering projects.
- Maintenance costs are zero making it cheap
What are the disadvantages of river restoration?
- Conflict in areas that are still being used by people.
- What defines valuable? This decision is left to the local environmental agency and if they make the wrong one, it can cause a lot of damage.
What are the causes of the Pakistan floods?
1) Monsoon rains more than 200mm were recorded in 4 days in several provinces.
2) Deforestation- Only 5% of Pakistan is covered by forest
3) Federal flood commission (FFC) was set up following previous floods, and received $900 million with documents showing that projects were initiated, funded and completed but little work was done to corruption.
What were the effects of the Pakistan floods?
- 7 million homeless
- 2,500 highways and 3,500 railways destroyed.
- 500,000 tonnes of wheat lost
- Taliban gaining support and social unrest
- 5,000 schools destroyed
- Food shortages
- Disease
What was the response to the Pakistan floods?
- 20% requested aid given by end of August
- 10 million forced to drink unsafe water
- Pakistani government blamed
