Equipment:
- Waders
- 2 ranging poles
- Meter ruler
- Tape measure
To measure the size of pebbles in certain sections of the river we had to pick up a pebble at random every metre across the river, we had to do this 30 times (if the river was to thin we would do it forwards and backwards until we had the correct number of pebbles) and then we would measure the width, height and depth of the pebble. The only exception to this was our third section of the river as the width of the river was only 2.2 metres in width and here we would select a pebble every ten centimetres.
Equipment:
- 2 ranging pole
- Metre ruler
- Tape measure
Results
Depth:
This is the result I got from measuring the depth of the first section of the river
Alyn.
These are the results I got from measuring the depth of the second section of the river
These are the results I got from measuring the depth of the third section of the river
These are the results I got from looking at the fourth section of the river
Pebble size:
First 30 pebbles at random from the first section of the river Alyn
First 30 pebbles at random from the second section of the river Alyn
First 30 pebbles at random from the third section of the river Alyn
First 30 pebbles picked at random from the fourth section of the river Alyn
VELOCITY:
Velocity of first section of river, overall velocity: 34.6 seconds
Velocity of second section of river, overall velocity: 56.8 seconds
Velocity of third section of river, overall velocity: 56.7 seconds
Velocity of fourth section of river, overall velocity: 53.5 seconds
To answer my first hypothesis (is velocity related to depth) I have decided to compare my average velocity for each river section with my average depth of each section
Section 1
Average velocity: 34.6 metres per second
Average depth: 6 cm
Section 2
Average velocity: 56.8 metres per second
Average depth: 18.3 cm (I had to not include some measurements due to the fact that this particular river had an island in the middle which made the results abnormal)
Section 3
Average velocity: 56.7 metres per second also abnormal due to the river being too small to get more than on area with a velocity)
Average depth: 1.2 cm
Section 4
Average velocity: 53.5 seconds
Average depth: 7cm
Looking at this, I can see that the depth of the river does not affect the velocity, for example with section three, the velocity is 56.7 seconds and the average depth is only 1.2cm. Whereas the velocity of section two similar to that of section three yet the depth of the river is 17.1 centimetres deeper, this information disproves my first hypothesis.
Second hypothesis: Do the particles in the bed load of a river become more rounded downstream?
Earlier I predicted that downstream the pebbles would become more rounded because of the friction they had endured, I am now going to investigate this hypothesis by studying my results after examining 30 pebbles at random from each section of the river. If my hypothesis is correct then the pebbles will also become smaller as they go downstream because they have been worn, and also most pebble measurements should be similar. Make sure this is correct I will put my results in a line graph and compare the peaks
looking at the peaks I can see that the further down the river they go the closer together the different line sections become, this shows that the pebbles are becoming similar to each other and also that the edges are becoming less jagged. With some peaks it does not show this but that could be because the stones have been deposited in the river some other way, I assume this because these peaks stand out more and are odd ones out. So therefore particles in the bed load of a river do become more rounded as they go downstream.
Third hypothesis: is pebble size related to discharge?
To calculate the discharge I have drawn river cross-sections for each section of the river. To draw these I have used my results and the rivers in comparison to one another are in scale. To find out the discharge I have to multiply the average velocity for each river section with the measured surface value which I calculate by calculating the area of the cross-sections which has water in. here is my table of results:
As I go further down the river the pebble sizes (in general) get smoother and smaller, whereas the discharge for each section has no pattern. This means that discharge is in fact, not related to pebble size.
Evaluation
I over-all think that my fieldwork went well even though there are several factors that I think would have to be considered if I were to do it again. For example the pebble sizes may not be completely correct due to the fact that not all pebbles have been caught in the river’s flow (some may have been thrown in there or have recently fallen from the rivers banks.) another factor that caused a problem was with the moel famau stream we visited. The width of the stream was a lot smaller than previous rivers we visited, and therefore made it harder to test velocity (the orange used was too large so we used a bottle cap instead) and also as it was only 2.2 metres wide, we had to convert it into centimetres. Problems such as these are to be expected though and cannot be helped. Factors that could perhaps be helped are things like the tape measure not starting at zero (mentioned earlier) to fix this problem we could perhaps attach string or some other kind of material to the end of the tape and fasten that to the poles instead.
Conclusion
Revisiting my information I have I have concluded that velocity is not related to depth. I have also proved that particles in the bed load of the river do become more rounded downstream. Finally, I have again proved my theory that discharge is not related to pebble size.
