Fieldwork Project on Hydrology by Peter Sacks
Submitted to St Paul’s as part of the Transfer Exam
2011
CONTENTS
INTRODUCTION
HYPOTHESES ........................................................................................................................................... 8
METHOD.................................................................................................................................................. 9
Depth .................................................................................................................................................. 9
Gradient .............................................................................................................................................. 9
Velocity (Hyrdo Prop) ........................................................................................................................ 10
RESULTS ................................................................................................................................................ 11
Depth ................................................................................................................................................ 11
Gradient ............................................................................................................................................ 11
Velocity (Hydro Prop) ........................................................................................................................ 11
Table.................................................................................................................................................. 11
DATA ANALYSIS ..................................................................................................................................... 12
Depth ................................................................................................................................................ 12
LIMITATIONS ......................................................................................................................................... 14
Depth ................................................................................................................................................ 16
INTRODUCTION
The Lake District is a mountainous region in northern England. It is a popular holiday
destination with many beautiful mountains and lakes. The most central area is called the
Lake District national park and was made a National Park in 1951. The Lake District is
entirely in Cumbria and the biggest National Park in England measuring 885 square miles. Its
features are results of the last Ice Age 10,000 years ago which include wide U-shaped valleys
where there are lakes and give the Lake District its name. The higher areas are rocky and a
lot of the land is boggy due to the large amounts of rainfall.
There are a few rivers in the Lake District and the River Eea is one of them. It is a small river
with a length of approximately 10km long. Its mouth is at Morecambe Bay and because it
originates in a bog it flows throughout the year.
To the west of the River Eea the geology is mainly slate but to the east there are
accumulations of limestone which sometimes make the river dry up.
The Source of the River Eea
This is a map of the 3 sites where we measured the River Eea. As you can see Site 1 and
Site 2 are very close together but Site 3 is a number of miles away.
River Eea just above Site 1
The River Eea just above Site 1
Mouth Of River Eea at Morcambe Bay 1
Overhanging Branches
Bridge
Wildlife (Ducks)
Plants
AIM
To investigate
changes in river
characteristics with
distance downstream
HYPOTHESES
 As stream order increases, channel depth
will increase
 As stream order increases velocity will
increase
 As stream order increases gradient will
decrease
METHOD
DEPTH
To measure the depth of the River Eea we put a metre ruler at a 90 degree angle to the
water with the 0 mark at the bottom of the river bed. Then we measured where the water
came up to on the ruler and noted it down. We divided the width of the river by 10 and took
the depth at each tenth interval. Then we averaged the readings for a mean river depth for
Meter Ruler
each site.
GRADIENT
To measure the
gradient of the
River Eea 2 people
spaced themselves
5 metres apart
each holding a
metre ruler in the
middle of the river
bed. The person at
the lowest level
rests
the
clinometer on their
metre ruler and
looks through the
eye-piece.
He
adjusts
the
clinometer
correctly so that it
is pointing to the
top of the other
metre ruler and
takes the reading.
We repeated this
three times and averaged the results.
Clinometer
VELOCITY (HYRDO PROP)
To measure the velocity of the river
we used both a Hyrdo Prop and the
“Dog Biscuit” technique but I am
only going to explain about the use
of the Hydro Prop. To use the
hydro prop we placed the impeller
in the water and measured the time
it took to travel along the rod using
a stopwatch. We repeated this at
1/3, ½ and 2/3 across the width of
the river.
Impeller
Hyrdo Prop
Rod
RESULTS
To work out the results a number of calculations needed to be made and I am going to
explain these.
DEPTH
To work out the depth from the data we had to take the 10 readings from each site and
average them to get our mean depth.
GRADIENT
To work out the mean gradient for each site we also had to take the 3 readings from every
one of the sites and average them.
VELOCITY (HYDRO PROP)
Determining the speed of the water in the River Eea was more challenging than the other
calculations we had to work out. First we had to find the average of all our times. Then we
took the length of the metal rod that the impeller span around when it was being pushed by
the flow of the water and divided it by the time the impeller took to get to the end of the
rod. Then we had to add the friction the of the impeller spinning round.
So the calculation works out like this:
0.0277 (friction) +[3.2805(length of metal rod)/avg time]
Once we had worked the calculation out we knew the velocity of the water in m/s
TABLE
These are the average results for each hypothesis that I have stated. I will be going into
more detail about the results in the next section, Data Analysis.
Depth
Gradient
Velocity (Hydro Prop)
Site 1
0.062m
10°
0.0531 m/s
Site 2
0.051m
12.3°
0.2207 m/s
Site 3
0.166m
11.6°
0.3089 m/s
DATA ANALYSIS
DEPTH
My hypothesis was: As stream order increases, channel depth will increase. I am going to
expand on this. Due to the fact that more tributaries enter the river as it flows downstream
the volume of water increases. As a consequence the flow of water speeds up and causes
more disturbance and erosion (Hydraulic Action, Abrasion and Corrosion) on the river bed.
I have constructed the graph so that the depths for each of the sites have a common centre
line to make comparison of the cross-sections clearer.
The average depth for Site 1 was 0.062m, Site 2 was 0.051m and Site 3 was 0.166m. Site 1
and Site 2, which are only 100 meters apart, show very similar profiles, although Site1 is
slightly deeper because at Site 1 there was a small waterfall and the plunge pool could have
caused erosion making the river deeper. Site 3 which is over 3 miles downstream does show
a significant increase in depth and width. Based on these facts, there was is a noticeable
trend when comparing the first two sites with Site 3, and my hypothesis is therefore partly
accepted.
GRADIENT
My hypothesis was: As stream order increases, gradient will increase. The reason this is
true is because rivers start in mountainous area and flow into flatter areas. The reason they
start in mountainous areas is because a lot of rain (relief rainfall) falls there and the water
travels downhill making streams and rivers.
Average Gradient (degrees)
Gradient of the River Eea
14
12
10
8
Site 1
6
Site 2
4
Site 3
2
0
The gradient at Site 1 was 10°, Site 2 it was 12. 3° and at Site 3 it was 11.6̇°. There is no
definite trend as Site 1 is 2 degrees flatter than Site 2. It think the reason for this is we had
to move position as a tree was blocking our line of site and some accuracy may have been
lost while moving about. Therefore my hypothesis is partly accepted.
VELOCITY (HYDRO PROP)
My hypothesis was: As stream order increases, velocity will increase. This is true because
the further downstream you go the wider and deeper the river is and therefore there is less
friction because there are less rocks to rub against and the river speeds.
Velocity of the River Eea
0.35
Average Velocity (m/s)
0.3
0.25
0.2
0.15
Site 1
Site 2
Site 3
0.1
0.05
0
The reading at Site 1 was 0.0531 m/s, at Site 2 0.2207 m/s and at Site 3 0.3089 m/s. There is
a definite trend in this graph as the velocity increases at each site. Site 1 and site 2 were
very close together so I expected the velocity readings to be fairly similar. The reason they
are not so similar is that at Site 1 there was a small waterfall and the plunge pool after it was
full of water not moving at all. For these reasons we only managed to take one reading from
Site 1 and it was very slow.
LIMITATIONS
DEPTH
The limitation of working out the depth of the River Eea with a metre ruler was that it was
very hard to keep it at exactly 90° to the water. Also the metre ruler was not very accurate
and we could only have a reading that was correct to 1 mm. Because Site 1 and Site 2 were
so close together it is difficult to draw any conclusions just comparing them and I would
have liked to take more readings at different sites.
GRADIENT
A limitation of the method was that the clinometer wobbled a bit whilst taking the reading
so it was sometimes quite difficult to have an accurate measurement. Also we had an
obstruction in the way so we could not take the reading and had to move. While moving we
lost some accuracy.
VELOCITY (HYRDO PROP)
There were a few limitations with the Hydro Prop. Firstly the Hydro Prop was very fragile
and could break very easily. What was worse was that if it did break they are very expensive
and costly to replace. Also they need a lot of current to spin (we had to push ours because it
sometimes got stuck and didn’t move, and it still took 2:09!) Another limitation was that on
one of the sites the water was not deep enough for the Hydro Prop to function and
therefore we could not take a reading.
CONCLUSION
I found out that the characteristics of the River Eea do change as you go downstream. 1 of
my hypothesis was completely accepted but the other 2 were only partly accepted. The
velocity of the River Eea consistently increases but the depth and gradient were not
consistent due to small waterfalls and obstacles blocking our line of sight.
This is a table showing which showing the hypotheses, whether they were accepted or
rejected and the reason why.
Depth
Gradient
Velocity (Hydro Prop)
Hypotheses
Increases/Decrease
Increases
Decrease
Increase
Hypotheses
Accepted /Rejected
Partly Accepted
Partly Accepted
Accepted
Reason Rejected
Tree in line of sight
Small waterfall
N/A
BIBLIOGRAPHY
http://www.panoramio.com/photo/47284280
http://www.panoramio.com/photo/47274577
http://www.britishwalks.org/walks/2003/429.php
http://www.met.reading.ac.uk/~swrhgnrj/pictures/lake_district/haweswater_and_small_water_tarn.jpg
http://www.labscientificequipments.com/meter-rule-wooden-7221.html
http://www.secure-server-uk.com/macommerce/product_info.php?products_id=87
http://www.flickr.com/photos/25993112@N06/3375844428/in/photostream/
http://en.wikipedia.org/wiki/River_Eea