Discharge is the amount of water passing a specific point at a given time and is measured in cubic metres per second. The discharge depends on the river’s velocity and volume. As the river moves down towards the sea its discharge will increases because of more water from the tributaries. This will lead to an increase in velocity and less friction with bed and banks so more energy in the river, which will lead to more erosion.
When we look at the velocity we can see it increased from 0.15 m/sec at the upper course to 0.51 m/sec in the lower course. The discharge increased from 0.00897 cumecs to 0.646 cumecs. We also worked out the hydraulic radius which shows how efficient the river is. This increased from 0.01812m to 0.15m. So the river was more efficient and there was more energy for erosion which led to an increase in the wetted perimeter from 3.3 metres to 6.4 metres to 8.6 metres in the lower course. Therefore all of the theory proved correct.
Our aim was to find out how the River Ffrwydwyllt changes from source to mouth.
The theory states that:
- The speed of flow should get faster from source to mouth. Also the fastest flow should be in the middle of the river except on a meander, where it is found on the outer bank.
- As you move downstream the channel off the river should get wider.
- Also the depth of the river should get deeper as you move down the river.
- As you move from source to mouth the load of the river should become smaller, rounder and smoother. This is due to erosion as the load moves down the river.
The reason why we decided to look at these points was because they would give us a good collection of data to work from.
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Speed of Flow – After collecting our measurements and analysing them, we could see that the results weren’t the same as the theory. The speed of flow was slower at the source than the mouth but in the middle course the speed of flow was faster than the lower course of the river. The reason for this was because of man. There is a man-made weir, which affected the speed.
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Width – The theory states that as you move downstream the width of the river should increase. I proved that the theory is correct. As the river went from source to mouth the width increased. There were no major problems which affected our results but the concrete block made it quite difficult for us the measure the width but we eventually did.
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Depth – The theory states that the depth of the river should increase as you move downstream. I have proved the theory is correct. There is no definite centre to the river so by including the measurements either side of the centre of the river; I have proved that the theory is correct.
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Load – The theory states that as you move downstream the load of the river should decrease. I have proven the theory correct. I calculated an overall average which gave us a better understanding. Also this made the results more accurate.
Linking Aspects of the River
As you move downstream the volume of the river increases. The reason for the volume increasing rapidly is because of the river’s tributaries where water comes from. Therefore more water means more energy, which means more erosion. There will be more energy to overcome the friction; which will cause more erosion by hydraulic action, sheer force of the river, corrosion and the rocks. This will cause the width to get wider and the depth to get deeper. The width in the upper course is 2.3m and the depth in the centre is 5.5m, the width of the middle course is 5.2m and the depth in the centre is 15m, and the width of the lower course is 8.8m and the depth in the centre is 28m. Also at the mouth of the river it has a greater discharge and a faster speed of low; the river will carry more material which means more energy to overcome friction so the speed of river increases. With all the energy and a faster speed of flow, this will cause the river to get wider and deeper. This is the link between the width, depth speed, volume, load and discharge which change from source to mouth.
Limitations
The river Ffrwydwyllt is quite a small river with not many tributaries which made it quite hard to worth with, so if I was to improve this project in any way, it would be to choose a bigger river.. the equipment we used to measure the river was very basic. If we had better equipment maybe our results would have been more accurate.
We could have also improved on where we measured the river. Sometimes when we were measuring the river there were man-made objects which made it quite difficult for us to measure. If I was to improve my results I would measure the river in a different place so nothing would be in the way.
One of the main problems was proving the theory correct. The speed of flow didn’t follow the theory because the middle course of the river was faster than the lower course. This was because there was a man-made weir which affected the speed. The width of the river did followed the theory, the depth also did because I included the two points either side of the centre of the river to be the centre because there is no definite centre. The load of the river also proved the theory correct by dong an overall average by man or nature. In the upper course there were lots of branches and bushes, and a man-made weir at the lower course of the river.
We could take this project further and take measurements on a bigger river to see if the results would vary. I would also use updated equipment such as a speed camera which would record the speed accurately and I would have picked average sized rocks for the courses to make the results more accurate.