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CONTINUED…read more

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V-Shaped Valleys
In the upper course of river the characteristic large sediment is usually only
transported when the discharge has risen as a result of heavy rain or snowmelt.
This bouncing and rolling of boulders and cobbles may cause vertical erosion,
which produces a relatively steep-sided V-shaped valley profile. The exact shape
depends on the following:
· Climate
Sufficient water is required for the high discharge levels needed to initiate vertical
erosion in the channel and to aid mass movement on the valley sides above the
eroding channel.
· Geology
The type of rock and it's structure may tend towards very steep sides (e.g. Limestone)
or gently sloping valley sides (e.g. Clays and mud).
More vegetated slopes tend to bind the soil better and may lead to more stable valley
Interlocking Spurs
These are also the characteristic of the upper courses of rivers. These form when the
river winds around protrusions, hills or ridges of land which appear to interlock
when viewed looking at a valley. A wider valley may develop with a near flat
floodplain where lateral erosion has widened the valley floor. The edge of the…read more

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Rapids are found when there is a sudden increase in the slope of the channel or where the
river flows over a series of gently dipping harder bands of rock. As the water becomes
more turbulent its erosive power increases.
This is a sudden fall of water that occurs where there are rapid changes in gradient in a rivers
course. They are most commonly found where there are marked changes of geology in
the river valley. Where resistant rocks are underlain by less resistant beds, the plunge pool
at the foot of the falls experiences the force of the swirling water around the rocks,
leading to more rapid erosion. This undercuts the beds above, leaving them overhanging
and prone to collapse. It is by this method that the waterfall retreats upstream, sometimes
leaving a gorge behind it.…read more

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When rivers are at bank-full stage
they may spill over onto
relatively flat land next to the
river know as floodplains.
Floodwaters are shallow with
extensive wetted perimeters
which means there is more
frictional contact and lower
velocities than in the main
channel. These factors combine
to deposit fine sediment over
the floodplain. As rivers migrate
across the floodplain over time,
they may leave pointbars on the
inside of meander bends,
adding to the extent of the
On some rivers dropping of
coarser material closer to the
river channel during a flood as
led to the development of
levées. First, the heavier
sediment carried by floodwater
is deposited, then the finer
sediment travels further over
the floodplain. Levées can be
artificially strengthened or
created to act as flood defences.…read more

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In places where the climate, geology and topography (arrangement of natural and artificial physical
feature of an area) combine to generate high sediment loads, braiding may occur. As water
levels fall and energy decreases, the rapid deposition of the coarsest load begins to block the
main channel. As the main river channel is no longer able to move the material, blocking its
path, then the stream subdivides into smaller channels to find the easiest route past the
obstructing sediment.
Deltas are areas of sediment deposited at the mouth of a river when it enters slow-moving
water such as a sea or lake and there is a decrease in energy. However, by nature they
are highly changeable landforms as they are composed of unstable, unconsolidated
sediments and therefore channel migration occurs.
Always remember that rivers are heading downslope towards the sea and will take the
easiest route to get there. As they head downslope there is a variation in geology and
typography so making it almost impossible to have a straight path. Even a channel
which is initially straight will deposit sediment when experiencing low flow conditions.
Once deposition has reduced the hydraulic radius of the channel, a riffle seems to have
water which flows inefficiently over it. Water needs to find a way around these areas of
high frictional contact, so it flows around them. Between these shallow riffle areas,
deeper sections are eroded called pools. Due, especially to times of high discharge a
series of pools and riffles develop over time. At times of higher flow the water swinging
around one side of a riffle will be propelled by centripetal force towards one of the
banks, eroding and undercutting it. An outer concave bank is created with a slower flow
on the inside bend leads to deposition on the inside bend. Helicoidal flow allows
material deposited from the outside bank to be deposited on the inside bank of the next
meander bank, and may become part of the floodplain.
Even where meanders are well developed, riffles may occur in the relatively straighter
sections of the channel between the meanders, as the outside bend is travelling at a
higher velocity, it erodes more effectively and carries the eroded sediment with it. On
the existing meander, the water enters a shallower section of the channel with a lower…read more

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Oxbow Lakes…read more

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