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South Wirral Geography - Water on the Land
Transcript of South Wirral Geography - Water on the Land
World's Widest - Iguacu Falls (Argentina) How waterfalls are formed (video) How Levees form - small animation (video) http://www.bbc.co.uk/scotland/learning/bitesize/standard/geography/rivers/river_landscapes_rev1.shtml Click on the link below for BBC bitesize Meander Cross-section our best known example in the UK! the location of the fast water (thalweg) erosion and deposition Don't forget the stories of William the water-droplet... A drainage basin diagram Hydraulic action
- the force of the water Abrasion - rocks scraping along the bed of the river Corrosion - minerals and salts dissolved from rocks and this causes weaknesses which can cause erosion Attrition - where rocks smash together and break apart Look at the image above!
(don't get these confused with methods of erosion!) News report from Friday 21st July (BBC) News report from
Saturday 22nd July
(SkyNews) Tewkesbury July 2007 Affected area Slip off slope on the inside of the bend
where material is deposited... Diagram to show formation Levees form during floods. They are small piles of sediment on either side of a river. They act to raise the capacity of the river (how much water it can hold). During a flood, any sediment that is being carried by the river is dropped on the river banks as the water goes onto the floodplain. Largest material is dropped first, then smaller particles.
(See diagram to left) Farms are rich in fertile sediment - they are perfect for the growing of crops. Without it's delta, Egypt would not be able to feed it's population. The Aswan Dam (further upstream), has been blocking the flow of the river and the delta is shrinking as it has less sediment reaching it. Gradually, the sea is attacking the delta and making it smaller - threatening the survival of many farmers and placing strain on the food supply of Egypt. 4 different ways a river erodes The water is able to smooth off and erode anything it touches. The water passing over the river bed and banks will wear away at them - given long enough this will be a significant source of erosion When a river transports material downstream, some of it will be scraping away at the river beds and banks. This will cause both vertical and lateral erosion to occur. When rocks are being carried by a river, they will sometimes smash together. When they do this they might break apart - this makes smaller and smaller bits of sediment. It is these small particles that will reach the estuary and then be moved around the coastline by longshore-drift, helping to keep beaches supplied with sand. Soluble minerals will dissolve in water. If a rock has soluble minerals within it, they will be leached out of the rock by the river water that is flowing around it. If this was happening then the rock would be weakened, making it much more likely to break up. Causes of the floods Effects of the floods Responses to the floods Social Effects Economic Effects Environmental Effects Short-term Long-term Weather? Saturated ground? Relief of the land? Land-use? The floodplain is the natural sponge that sits either side of the river. It is where excess water that enters the river is stored when bankfull level is reached. It is important that they are left to absorb water. Humans are sometimes really daft, and build houses and towns/cities on floodplains. Then, when they get flooded they are surprised! duhhhhhhh... A river may be flowing over layers of hard and soft rock. The water begins to erode the softer rock. A plunge pool will be created by hydraulic action and abrasion. As water enters the plunge-pool, there will be some splash-back which further erodes the layer of soft-rock. The hard-rock layer is left above, unsupported - this is an overhang. The overhang will break off and drops into the plunge-pool.Now, the whole waterfall has retreated backwards. If this continues, the waterfalll will get higher and a gorge of recession will be formed. Meanders are bends in a river. They occur when rivers start to change course. Water can be deflected to one river bank - here it begins to erode the bank sideways. The water bounces from this bank to the other. River bank River bank Flow of water The water erodes the river banks that it is bouncing off. This is now the outside of a newly formed river bend. On the other side of the bend is where there is now less water, so sediment begins to build up at this point. Deposition of sediment here... The process continues, with erosion on the outside of the river bend and deposition on the inside. Given long enough, the rivers bend will get more extreme - and eventually a meander as shown in the photo above might develop. Erosion here... The long profile of the river shows a side-view of the river, from top to bottom - from source (in the mountains), to estuary (at sea-level). It can be divided into 3 main sections, the Upper, Middle and Lower courses.
In the Upper course, waterfalls are common - they are a landform associated with Erosion (the dominant process in this part of the river.) In the Middle course, Meanders are common - they are a landform associated with both erosion and deposition of material. Despite this, the dominant process occurring in the middle course is Transportation A different way of showing the whole length of the river is like this. Causes of floods General problems caused by all floods Heavy rain /precipitation Too much discharge - bankfull level exceeded Impermeable surfaces - bedrock and man-made (towns) Dam bursts (very rare) - although sometimes water has to be let out of reservoir during heavy storms Drains may become blocked - fat, sanitary products, wet-wipes are particular problems for drains. Levees may break Land-use - what the land is used for - farms, housing on floodplains? Steep land? Deforestation Related to the Environment (built and natural) Related to people Related to money and the economy Plants and habitats are disrupted - animals may starve, migration away from danger by animals Crops may be destroyed in the fields Flood damage to buildings - electricity cables damaged, water supplies contaminated, decoration affected, plasterboard 'blows', wood rots Transport infrastructure affected, roads blocked, trainlines under water Homelessness created by damage to houses Unable to work due to inability to travel Emergency services placed under strain Deaths - some people may drown, likely to be those trapped in some way, or very young unable to swim the ill - people unable to get to hospital/doctors, (pregnant women?), organs unable to be transferred. Ambulances unable to reach needy (heart-attack victims) Old people may need to be evacuated Education affected (schools closed) Cost of repairs - to buildings Insurance premiums likely to rise due to claims and might be difficult to get insurance in the future. Local and national economy is affected - people are unable to work, or spend in shops Businesses might not be able to cope with the losses and they might go bust... V shaped valley formation video The Topic Summarised in a different format, which can also be downloaded from Geography GCSE Moodle Page Learn these things and ace the test! They can't ask you anything not on here - check what you understand or don't understand then do something about it