Investigate how features of a river change over distance
Geographical understanding
I have broken the hypothesis up into small sections to give my controlled assessment more
structure than it would otherwise not have. The smaller section consists of the cross section
of a river, the velocity of a river, the discharge of a river and the size of a flood plain.
Key ideas
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Cross section increases downstream
Velocity increases downstream
Discharge increases downstream
Floodplain size increases downstream
Key ideas
Cross section increases downstream
During the upper course of the river the river channel is narrow and shallow, which
means that the cross section is low. Moreover the bed load will be large and angular,
which will lower the cross sectioned area even more if they are present.
Furthermore as the river moves downstream the width and depth of the river
increases which consequently increases the cross sectional area of the river. In
addition to the width and depth increasing the bed load will become more rounded
and smaller, which will increase the cross sectional as there are less things blocking
the rivers flow and lowering the cross sectional area. Also in lower course of the river
the cross section will be most likely be at its highest, as it will have the biggest depth
and width in this part and the bed load will not be affecting the cross section as they
are small and round so having little effect on the cross sectional area. The main
causes for the widening and deepening of the river are abrasion and hydraulic
action, the hydraulic action is the pressure on a crack widening it and this will be
acting on the river side’s and river floor meaning that as the river widens and
deepens the amount of hydraulic action will increase as there is a higher volume of
water. One of the other causes for the widening and deepening of the river is
abrasion which is the rubbing of the bed load with the river bed and rivers sides
causing friction and the wearing away of the sides, which leads to the width and
depth increasing so that the overall cross section increases.
Velocity increases downstream
The velocity of the river will change as it moves down stream as during the upper
course the river will have a large wetted perimeter meaning that there will be a large
amount of friction acting on the river. During the middle course of the river the
wetted perimeter is bigger but so is the volume of the river so even with the added
friction the river still increases in velocity. Moreover during the lower course of thee
river there is a much larger volume of water than wetted perimeter causing the
water to be crammed and consequently move faster. Furthermore the tributaries
will add to the volume of the river, and so will the momentum of the river as the
larger the momentum the larger the force of the river meaning that the velocity will
have increased.
Discharge increases downstream
The discharge is the cross sectional area x the rivers average velocity at any
particular point in a river, and as the river goes from the upper course to the middle
and then lower courses the channel gets wider and deeper as I mentioned earlier,
which will mean that the cross sectional area increases and consequently the
discharge increases. Moreover the discharge increases downstream as the velocity
of the river increases because of the decreased wetted perimeter which is lowered
by the reduction in friction, increasing the channel efficiency. Furthermore the
tributaries will add to the volume of the river, as they will increase the cross
sectional area as they are adding more water to increase the volume of water within
the channel of the river.
Floodplain size increases downstream
As the river goes downstream the volume and speed of the river increases so that
when the river floods it does it with increasing strength and so as it goes
downstream there will be added erosion causing the surrounding area to be eroded
away and so creates a level area which gradually gets bigger as the river goes from
the upper course to the middle and then to the lower course.
The Bradshaw model
The Bradshaw model is a diagram depicting how a rivers characteristics will change as the
river progresses downstream from the source to the mouth. What I expect to see is that the
cross sectional area will increase as the depth and with of the river increases, I also think
that the discharge, wetted perimeter, depth and width will all also increase as it goes down
stream because of increasing velocity and erosion the depth and width will increase causing
the wetted perimeter and discharge to increase. Moreover, I think that the stone
size/angularity, gradient slope and turbulence will decrease as the stones will become
smaller and more rounded by erosion which will lead to the stones not being above water
causing more turbulence and the gradient will decrease as it will be cutting downwards
more at the source then by the mouth as it wants to reach sea level faster at the upper
course.
Map
The general location of the river Goyt is located near Manchester in the north west of
England. It was chosen as the place for our river study as it was possible to do in a day and
showed most features a river is capable of having and meets the requirements that it has to
have to use as our case study.
Zoomed out view of the river Goyt and view of the county it is in
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area it is
located
A view of the area around the studied parts of the river Goyt
Mouth of the river
= River
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source/
mouth
Source of the river