As level Geography Hydrology notes with case studies

For the WJEC hydrology 

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The water cycle is the system of inputs and
outputs in the atmosphere, land and ocean.
Inputs to the atmosphere are evaporation
from land and ocean and transpiration from
trees with the outputs being precipitation to
land and ocean. The inputs to land are
precipitation and outputs are evaporation,
transpiration to the atmosphere and run off to the ocean. The inputs to the ocean are therefore
precipitation and runoff and the output is evaporation. The stores in the atmosphere are clouds
(water plus ice within them) on land it is in rivers, lakes, ground water and soils. The ocean itself is a
store. Man has modified this through use of sewage systems providing extra inputs and outputs.
However cycle is still a closed system with the amount of water fixed. Precipitation is any rain, snow
or hail.
A drainage basin the catchment area of water for a river, most precipitation in a drainage basin will
drain into the main river either directly or from one of the tributaries. The watershed is the boundary
of the basin . The water table is the level of ground water stores. There are 2 main types of rain fall,
relief where rising air cools over hills causing rainfall and frontal rainfall caused by the boundaries of
cold and warm fronts. There are 3 main types of flow in hydrology;
Overland flow- When water runs off hills and flows above the ground. It is the quickest flow
and will mean water getting into the main channels quicker. It happens more when the
ground is impermeable stopping water infiltrating into the soil such as when it has been built
upon , is saturated, rainfall is heavy, slopes are steep and the soil is clay like. The more
overland flow the more likely it is that a river will flood.
Through flow- When water flows through the soil to reach main channels, The more water
that infiltrates the soil the more it happens and the less that percolates into the bed rock.
Less will percolate with impermeable granites, steep slopes and saturation. This is a medium
speed flow.
Ground water flow- When water flows through the bed rock, the more water that
percolates into the bed rock the more of this that takes place. Maintains the rivers base flow
in times of drought.
Other processes include transpiration which is when water evaporates from plants (the hotter and
windier the more of this) and interception- when water is taken out of the soil to be used by plants.
There higher the density of plant life the more interception.
A storm hydrograph shows the discharge amount in a river compared to rainfall and time. The rising
limb is where discharge increases, the steeper the quicker it happens. The discharge of a river will
rise quicker the more overland flow that happens so the steepness is based on the factors that
affect the amount of overland flow.
The water budget uses a river regime of an entire year When precipitation is greater than
transpiration there is a water surplus, when the opposite is true there is soil moisture utilisation until
the store is used up which leads to a discharge then recharge until the stores are full.

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Flooding case studies- Gloucestershire 2007
Soil moisture highest for 50 years
Record rain from May to July of 414mm
2 months rain fell in 14 hours on the 20th of June
Saturated ground in the south west unable to cope with this causing saturated overland flow
and lots of water entering the Severn river causing it to burst its banks causing fluvial
flooding in places like Tewksbury
Changes to the land use of many floodplains from arable to residential meant less infiltration
happened causing…read more


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