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A-level Geography Revision - Coggle Diagram
A-level Geography Revision
Niagara Falls
It is the result of undercutting of resistant rocks
The river flows for about 50km between Lake Erie and Lake Ontario.
It flows in a 2km wide channel just 1km above the falls
The course of the Niagara Falls was established about 12000 years ago
The Niagara Falls started to form when when water from Lake Erie began to spill northwards into Lake Ontario. When this happened, it passed over the highly resistant dolomitic (Limestone) escarpment
Over the last 12000 years the Falls have retreated 11km, giving an average rate of retreat of about 1 metre per year.
Water velocity accelerates over the Falls, and decreases at the base of the Falls
Hydraulic action and abrasion have caused the development of a large plunge pool at the base.
The fine spray and eddies in the river help to remove some of the softer rock underneath the resistant dolomite. As the softer rocks are removed, the dolomite is left unsupported and the weight of the water causes the dolomite to collapse. Hence the waterfall retreats, forming a gorge of recession.
The amount of water flowing over the Niagara is now controlled due to the construction of hydro-electric power stations.
Nile delta
Under threat from rising sea levels and global warming
The delta is one of the most fertile tracts of land in the world
Coastal erosion is steadily eroding it in some places at a rate of almost 100 metres per year. This is partly due to the annual deposits from the Nile floods
The delta is home to about 50 million people living in densities of up to 4000 people per km squared
The Intergovernmental Panel on climate change has declared Egypt's Nile delta to be among the top three areas most vulnerable to a rise in sea level.
About 270km of the deltas coastline is at a dangerously low level.
A 1 metre rise in sea level will drown 20% of the delta
The delta is also suffering from a number of environmental crises including; flooding, coastal erosion, salinisation, industrial/agricultural pollution and urban encroachment.
Saltwater intrusion is destroying crops
Egypt's population of 83 million is set to increase over the next two decades.
Today, Nile water barely reaches the end of the delta.
Many people have extracted water supplies upstream, and what water does make it downriver is increasingly polluted with toxins and other impurities.
Aral sea
It began shrinking in the 1960s when Soviet irrigation schemes took water from the Syr Darya and the Amu Darya rivers
By 1994, the shorelines had fallen by 16 metres
Increased salinity levels killed off the fishing industry
Salt from the dry seabed's has reduced soil fertility and frequent dust storms are ruining the region cotton production.
Drinking water has been polluted by pesticides and fertilisers and the air has been affected by dust and salt
Kissimmee
The 165km long river once meandered through central Florida
Its floodplain, reaching up to 5km wide, was inundated for long periods by heavy seasonal rains. Wetland plants, wading birds and fish thrived there, but the frequent prolonged flooding caused a severe impact on people
Between 1962 and 1971, engineering changes were made to deepen, straighten and widen the river, which was transformed into a 90km, 10 metre-deep drainage canal.
Impacts of channelisation
The loss of 2000 to 14000 hectares of wetland
A 90% reduction in wading bird and waterfowl usage
A continuing long-term decline in game fish population
A massive restoration project was started in 1999, on a scale unmatched elsewhere. The project restored over 100km squared of river and associated floodplain wetlands. It benefits over 320 fish and wildlife species, including the endangered bald eagle, wood stork and snail kite. The project was completed in 2015.
It is estimated that the project cost over $400million
Benefits of restoration
Higher water levels should support a natural river ecosystem again
Re-establishment of floodplain wetlands and the associated nutrient filtration function is expected to result in decreased nutrient loads to Lake Okeechobee
Populations of key avian species, such as wading birds and waterfowl have returned to the restored area
Dissolved oxygen levels have doubled which is critical for the survival of fish and other aquatic species.
Bangladesh
60% of the land is less than 6 metres above sea level
It has a high frequency of floods and cyclones
Several regions affect conditions within Bangladesh:
High plateau of Tibet - the source of the Brahmaputra, where most of the river flow derives from snow melt and glacier melt
Himalayas - source of the Ganga and many of the springs that feed into the Brahmaputra
Ganga plain - one of the largest lowland areas in the world, and a region of intense cultivation
Meghalaya Hills - located between the floodplain of north-east Bangladesh and the Indian lowlands of Assam; rise to a height of 2500m and act as a barrier to the monsoon winds from the Indian Ocean
Causes of flooding
Flooding in Bangladesh alternates between periods of high flooding frequency and low flood frequency
Floods in the western part of Bangladesh were more intensive in the 18th and 19th centuries than in the 20th or 21st centuries
Massive floods occurred regularly long before human impact on the watershed began
The variation in the extent of flooding year by year has been increasing since the 1950s