Water On The Land Flashcards
(47 cards)
What is river flooding
Occurs when the volume of water present in the channel is too great to remain there and
so the river overflows onto the land that is not normally covered by the river
What is one physical cause of flooding
Prolonged rain
Rain for a long period of time means the ground will be saturated and infiltration will not be able to occur, causing rapid surface runoff
Explain how an ox-bow lake and a meander scar formed
A meander is formed in a river, due to the inside bend moving much slower than the outside bend. As it moves a meander neck is formed. Overtime the two sides of the meander neck comes closed together, until only a small piece of land is separating them. This barrier is brocken down during a storm when the river overflows. There is now a circle in the river . Because it is quicker to cut straight through the loop, the water does not travel through what was once the meander. As time goes the once meander gets speared from the river, creating an ox-bow lake. As the water in the ox-bow lake drys up a meander scar is formed
Describe how river transports it’s load
A river transports large boulders via traction, where materials are rolled along the bed.
Smaller pebbles are carried by saltation which in a leapfrog motion
Explain the formation of levees
During floods the river bursts it’s banks and as a result there is a loss of energy.
This means that the river can no longer carry the material it was transporting so deposition occurs, the largest material carried is left behind first.
It is this material that begins to build up the banks.
This happens a number of times and there is a build-up of layers of material and so the levee gets bigger and becomes more apparent and reformed
Explain the formation of a flood plain
They from due to both erosion and deposition.
Erosion widens the valley taking away the interlocking spurs present near the source and creating wide, flat area next to the river.
Deposition is also partly responsible for the formation of a flood plain. When the river overflows, material being carried is dropped as energy is lost. Over time, this sediment forms layers on the flood plain, building it up.
Formation of a gorge
Horizontal layers of hard and soft rock, with the hard rock forming the cap rock.
The erosion of the underlaying softer rock happens at a faster rate causing an overhang to develop
Abrasion and hydraulic action are particularly important processes of emotion in the formation of a gorge
Material from overhang collapses causing the waterfall to retreat.
The process begins again and repeats, subsequent collapses lead to the formation of a gorge
Issues of building dams and reservoirs
Economic-issues may refer to cost of building dam and pipelines; loss of farmland and livelihood versus opportunities for development of tourism.
Social-issues may refer to the loss of people’s homes and displacement of people as villages are drowned; ill-feeling regarding the origin of water and its destination such as reservoirs in Wales and Welsh water supplying England.
Environmental-issues likely to refer to loss of land and habitat, impact on the flow of the river and impact of new uses such as recreation and tourism; reduction of flood risk.
Process of carbonation
Limestone is calcium carbonation. A rain water falls it mixes with the CO2 in the atmosphere to create a weak carbonic acids. Calcium carbonate is insoluble in the process of carbonation. Limestone has joints and is permeable, the water enters via these joints and they get bigger as the limestone solution is made and the dissolved limestone is removed. This results in the enlargement of gaps between the limestone blocks. The surface of the clients is smooth due to water, however it is often uneven and pitted due to the impact of solution where the water sits in hollows.
Formation of interlocking spurs
That main process at work is the vertical erosion of the steam bed.
This cuts into the landscape deepening the valley sides.
As the water twists around rocks or boulders the erosion forces undercut outward bends and a snaking pattern is produced.
From lower down the interlocking of the spurs of land between the bends blocks the view.
Explain the formation of a waterfall
The sudden and often vertical drop of a river along its course.
When resistant rock overlays least resisting rock, a waterfall can begin to form.
The soft rock is being eroded manly by hydraulic action and abrasion.
The cap rock forms an overhang as as weathering continues. A plunge pool is developing at the base of the waterfall.
The overhang becomes too heavy and collapses into the plunge pool.
The plunge pool enlarges due to the continued erosion.
The overhang continues to fall, the waterfall therefore retreats upstream leaving a steep sided gorge of recession.
Why do most rivers not respond to rainstorms immediately?
Lag-time; take time far water to enter by surface run-off, through flow and takes the longest through ground water flow.
What might influence discharge?
Human influence-humans can either increase the discharge (e.g. at a sewage outfall) or decrease the discharge (e.g. abstraction of drinking water)
Land use-discharge is higher in unvegetated, urbanised and deforested basins because there is a greater surface runoff.
Rock type and structure-Rivers in areas of impermeable rock will have more water in them than those with permeable as they do not allow water to soak in, so water flows quickly over the surface to the channel.
Rocks like limestone have joints and bedding planes that provide pathways for water to enter and go through, so water is removed from the surface and takes a slower route to the river, so there is less water present in the channel.
Tributaries-the precise increase in discharge when a tributary meets the main river depends on the size of the tributary; small first.
The amount of water fluctuates due to a variety of factors.
For example prolonged rain, hurricanes, heavy wind, temperature increase, and land uses (such as easily accessible and visited frequently).
Describe and explain the human factors that can increase the risk of flooding.
Urbanisation increase the risk of flooding. This is because towns and cities have more impermeable surfaces and therefore no water can be absorbed and increased surface runoff. Deforestation will also increase flooding risks. This is because by removing trees you reduce the amount of water intercepted and you increase surface run-off.
Comparisons between the causes of the flooding in Queensland and in Bangladesh:
- Heavy rain
- Global warming attributed to higher intensity of rainfall
- Building on flood plains
Contrasts between the causes of the flooding in Queensland and in Bangladesh:
-Queensland=16cm of water in 36hrs
Bangladesh=35cm of water in 24hrs
-Queensland experienced La Niña weather ever increasing rainfall
-Bangladesh has issue of deforestation in Nepal, low lying land
Comparisons between the effects of the flooding in Queensland and in Bangladesh:
- People died (although in Bangladesh more)
- Both affected large areas, 3/4 Queensland, 1/2 Bangladesh
- Farming affected, wheat in Queensland and rice and cash crops in Bangladesh
- Mud/debris left behind
Contrasts between the effects of the flooding in Queensland and in Bangladesh:
- 35 deaths in Queensland, 600 in Bngladesh
- 100, 000 homes were effected, no electricity in Queensland, 30 million homeless in Bangladesh electricity off for several weeks
- A$ 19billion in Queensland, $7billion in Bangladesh
- Causes water born diseases e.g. Diarrhoea in Bangladesh
Comparisons between the responses of the flooding in Queensland and in Bangladesh:
-Both use hard engineering. Dams in Queensland and flood embankments in Bangladesh
What were the physical causes of flooding in Bangladesh?
Torrential rain (1m per day) (heavy monsoon)
Giant flood plain
Very flat/low lying land
Cyclones common
1.7million km2 drainage basin-12x bigger than Bangladesh and 7x bigger than in the UK
What were the human causes of flooding in Bangladesh?
Increase in population-land has to support more people, which reduces interception, increases surface runoff. Soil erosion, rescues discharge capacity.
Deforestation-water moves quicker (Bangladesh, tibet, Nepal) 150 million trees or more
Urbanisation-more surface runoff, impermeable surfaces
Change in agricultural methods
Global warming-melting glaciers-snowmelt
Impacts of flooding in Bangladesh
Deaths
Debris
Farming destroyed
Hard engineering projects in Bangladesh to stop the flood from being as bad the next time
Flood embankments on the West Bank (because it is the more expensive land) Drainage basin Land raised flood levels People provided with housing, community facilities by NGOs (non-governmental organisations) Flood shelters New channels Underground drainage Flood protection facilities
Soft engineering in Bangladesh
FARUK’S FISH-able to move the cages where the fish are kept, so it is not lost when the loads come along. NGOs provided the cages and training on how to use them.
NOOR’S SUPER DUCK-sells 200-400 eggs a day. The duck’s are able to survive the floods.
MOSHIUR’S PUMPKINS-NGOs train the locals teaching them what to do. Using land no one else wants due to the infertility. Sand bar cropping. The pumpkin growing cycle fits in with the flood cycle. The pumpkins are easy to store.
