Changes in the Water Cycle over time (Natural and Human Impacts) Flashcards
3 natural causes of changes in the water cycle over time
Droughts
Storms
Seasonal changes
What is a drought
A period of below-average precipitation in a given region, resulting in prolonged shortages in the water supply (e.g atmospheric water/ surface water/ groundwater). A drought can last between 15 days and several years
How long can droughts last for
Between 15 days and several years
Does vegetation gore more rapidly in the summer or winter
Summer
Are storms more frequent in the summer or winter
Summer
Are there higher levels of rainfall in the summer or winter
Winter
2 human changes (changes in land use) that cause changes in the water cycle over time
Deforestation
Soil drainage
Why does localised (small scale) deforestation lead to increased overland flow
There is less vegetation to intercept the rainfall and there is less evapotranspiration meaning that a large volume of water reaches the ground all at once and cannot all infiltrate into the ground
Why does localised (small scale) deforestation increase the rive discharge
There is less water being intercepted by the trees and less evapotranspiration so more overland flow. This means more water ends up in the river instead of being continuously recycled between the forest and atmosphere
What is the aim of soil drainage
To reduce the water table in the soil through the installation of tiles (tubes) to prevent the soil from becoming waterlogged and to allow plants and agriculture to grow
Why is a high water table in the soil bad for farmers
When the soil is waterlogged, less oxygen becomes available on the soil for plant roots which can prevent the crop from growing and reduce crop yield
Why is it good if there is more oxygen available in the soil due to a lowered water table created by soil drainage
It creates aerobic conditions so that more microorganisms can grow. This increases the rate at which organic matter is broken down into organic humus and plant nutrients are mineralised into an available form
Why is it bad if the topsoil can dry out due to a lowered water table from soil drainage
The top layer of dry soil which contains nitrates from fertilisers can be blown away and end up in ponds and rivers. Nitrogen causes eutrophication which can cause aquatic life to die, effecting ecosystems
What is water abstraction
The process of taking water from any source, either temporarily or permanently (mostly for agricultural use and domestic water supplies)
What has caused fluctuations in the groundwater levels in the London Basin over time
Varying levels of abstraction
During the 19th century and early 20th century industrialisation occurred which led to the basal-sands aquifer becoming increasingly exploited. At the peak of abstraction, groundwater levels beneath central London dropped to 88m below sea level creating a low water table
Since the mid 1960s, changes in economic activity such as brewing industries relocating and closing down led to less water abstraction and groundwater levels recovered by 3 metres per year by the early 1990s. This led to a high water table under London and posed a threat of rising groundwater to London Underground and building foundations.
As a result of this high water table and threat, the GARDIT (General Aquifer Research Development and Investigation Team) strategy was put in place to control water levels through careful management of abstraction and artificial recharge
What is teh main aquifer under the London basin
The chalk-basal sands aquifer
During the 19th century and early 20th century what were the groundwater levels like beneath central London and why
Very low
Industrialisation meant that the chalk-basal sands aquifer under the London basin was becoming increasingly exploited e.g to be used in the textile and coal mining industries
At the peak of abstraction groundwater levels beneath central London dropped to 88m below sea level creating a very low water table
From the mid 1960s to 1990s what were the groundwater levels like beneath central London and why
High
From the 1960s, a change in economic activity (e.g brewing industries relocating and closing down) led to less water being abstracted so groundwater levels recovered by 3m per year by the early 1990s.
This led to a high water table under London
Since the 1960s, changes in economic activity have led to less water abstraction and groundwater levels under London have been recovering and increasing the water table.
Why does a high water table under London pose a threat and what is being done about it
If groundwater levels continue to rise it could damage the London Underground infrastructure and building foundations.
The GARDIT (General Aquifer Research, Development and Investigation Team) strategy was put in place in 1992 to control water levels through careful management of abstraction and artificial recharge.
What does GARDIT stand for (the strategy used to control water levels in London so that rising groundwater levels wouldn’t cause damage to the London Underground tunnels and infrastructure or building foundations etc)
General Aquifer Research, Development and Investigation Team
