Geography Revision

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Inputs & Outputs
A drainage basin is an open system meaning it has inputs and
outputs. The most obvious input (at least here in Britain) is
rain but snow, hail & dew all act as inputs too. These inputs
(including rain) are grouped under the term precipitation, water
that falls or condenses on the ground. Basins also have
outputs that are, again, pretty obvious. Evaporation is a big
one, where water turns into a gas and become part of the
atmosphere. Transpiration is similar to evaporation but is the
loss of water as a vapour from plant and tree leaves. The
combined effect of evaporation and transpiration is
called evapotranspiration . The final output, the one that a lot
of people forget, is water flowing out of the basin. The
technical name for this is river discharge.
Stores
A store is a way of storing water in a drainage basin. There's a
couple of different types of water storage. One is vegetation
storage . Vegetation lives off of water right? Well, any
vegetation in a drainage basin will take up precipitation and
store it, simple. The vegetation storage is the total volume of
water stored in the vegetation in a basin at one time.
Vegetation provides another type of storage too, intercepted
storage . Vegetation doesn't store all of the water it comes into
contact with, some of it is intercepted by leaves where the
water will remain until it evaporates or falls to the ground.
Although vegetation is the most common interceptor of water,
buildings and other structures will intercept water and act as
stores too.
A lake or a pond is another type of storage as is their smaller
cousin, a puddle. Yes puddles are small but they all add up to
form surface storage . This can be a significant percentage of
the total amount of water stored in a drainage basin. In
addition to being stored on the surface, water is stored in the
ground too. This is known as groundwater storage . This could
be water that has been absorbed by the soil or it could be

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You may have heard of a
little something called the water table. The water table is a
form of groundwater storage made up of lots of aquifers
(permeable rocks) that have had their pores filled with water.
The final sort of storage is so obvious it isn't obvious.…read more

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The speed
of interflow and groundwater flow is highly dependent on the
permeability of the rocks the water's travelling through. These
processes are normally very slow but permeable rocks will
make them faster2
. Vesicular3
rocks, such as pumice or
vesicular basalt, allow water to percolate far more easily than
rocks like granite, which aren't vesicular.
There's two more type of flow that we haven't discussed, the
first is stemflow. Like channel flow, the name's a bit of a
giveaway with this one.…read more

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I'm referring to the amount of water stored in the
soil with respect to precipitation, evapotranspiration & run off.
In the UK, or any place with a relatively temperate climate, the
water budget changes in a predictable pattern throughout the
year as the seasons (and hence the weather) change. In the
winter months, there's a large volume of precipitation but little
evapotranspiration. This is primarily due to the colder, wetter
climate and shorter daylight hours.…read more

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The discharge of a river changes over time depending on a
few factors. The most influential factor is the weather. After
heavy rainfall the discharge of the river will be higher because
there's more water entering the river. The weather affects
discharge so much that there's a special graph that we can
draw called a hydrograph which shows precipitation and
discharge on the same graph and makes it easy to see how
quickly precipitation affects the discharge of a river.…read more

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This
is because all points in the drainage basin are (again, roughly)
equidistant from the river so all the precipitation reaches the
river at the same time.
The size of the drainage basin obviously has an impact on the
hydrograph. Large basins will have high peak discharges
because they catch more precipitation but at the same time
they'll have longer lag times than small basins because the
water takes longer to reach the rivers.…read more

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Weather & Climate
The intensity of a storm will obviously impact the peak
discharge of the river. More rainwater = more water in the river
so a higher discharge. Not immediately obvious is the type of
storm (or precipitation) that takes place. A winter storm (i.e.
snow) will result in an increase in the river's discharge when
the snow melts but this often won't be for a long time, so the
lag time will be huge.…read more

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Easy marks. The ever so slightly harder
questions are the ones that ask you to explain a hydrograph
because these require you to think. Let's look at the storm
hydrograph for the fictional River Shui again:
If asked to describe the hydrograph you could quote the lag
time, peak discharge and comment on the steepness of the
rising and falling limbs (remember, state values off of the
graph). Instead, you could be asked to explain the
hydrograph's shape.…read more

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This
type of erosion is strongest at rapids and waterfalls where the
water has a high velocity. The next type of erosion
is corrasion1 . This is where the river's load acts almost like
sandpaper, removing pieces of rock as the load rubs against
the bed & banks. This sort of erosion is strongest when the
river is transporting large chunks of rock or after heavy rainfall
when the river's flow is turbulent.…read more

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Slightly smaller particles, such as pebbles and gravel, are
transported by saltation. This is where the load bounces along
the bed of the river because the river has enough energy to lift
the particles off the bed but the particles are too heavy to
travel by suspension.
Fine particles like clay and silt are transported in suspension,
they are suspended in the water. Most of a river's load is
transported by suspension.
Solution is a special method of transportation.…read more

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