Hypothesis
- I expect the width of the river to increase as the river flows further downstream. As tributaries join up with the main river, meaning that there is a greater volume of water flowing down the river, and as a result there is more erosion and the banks are wider. I think that the width will increase because as you go downstream more tributaries will join up the river and there will be a larger volume of water flowing through the river channel, meaning that it needs to be widened to support the volume of water. There will also be a bigger velocity further downstream, so the water particles will hit the bank harder, and wear it away more. Also when the river is larger it is able to carry more material meaning that more corrosion occurs, which is when materials rub against the riverbank and wear it away.
- The river will deepen as the river flows downstream, as vertical erosion is taking place, which wears away the riverbed and makes it deeper. I also predict that the river is made deeper by traction, which is when large boulders are rolled along the bed of the river causing them to wear away the riverbed and make it deeper. Corrosion is also occurring, which is also on the riverbed, wearing it away further. Moreover the river will deepen downstream simply because there is a greater volume of water, so it will have to deepen and widen slightly to support the water that it gains from all the tributaries that join it.
- I would expect the speed of the river to decrease as the river flows downstream, as the river flows fast at the source because the source is usually at a high up place, so gravity will naturally speed up the water, whereas when it is downstream the water is flatter so gravity is not acting on it as naturally. This means that the river will require more energy to move as fast as it did at the source. However all rivers are different, and as the river is only 12 miles long the source may not have such a high starting point, so as the river flows on the river may speed up due to the sheer volume of water behind them.
- I predict that the river will meander more when the river flows further downstream. I think this because there is a greater amount of erosion and more water is pushed to the side, a process called lateral erosion occurs. However on the other side there is much less water, and as a result a large bend or meander is formed out of the rock.
- More point bars and river cliffs will be found downstream. As there will be more meanders, causing the slower water to flow done one side of the river channel, and drop its bed load forming a point bar. The faster water will flow down the outside, causing the river to meander more. That will mean that the faster water will flow on the outside, so when the water turns it will hit the bank causing river cliffs to form.
- I predict that the river will become deeper and wider as the river flows downstream, as there is a greater volume of water, which results in more erosion, meaning that the sides and bed of the river to wear away more to make it deeper.
- As the river flows downstream the gradient may decrease. However all rivers vary, so the source may not be in a high up place, for instance the river we are studying is only 12 miles long, which is relatively short. So the water may not start in such a high up place before flowing into the sea. However if it is in a high place the gravity will make the river flow faster. When the river is flowing downstream it tends to flatten out, which would mean that gravity is not acting on it as much, but it is joined by tributaries, and the volume of water particles behind the river may make it flow faster, with more currents being formed as they flow closer to the sea.
Site 1: Ocknell Plain
Description: The above graph shows that the maximum depth of the river is 70cm, with a minimum of 55 cm. The river falls steeply at one side, which could be due to river cliffs being formed. The river has no water in it at the moment, which could be because there has been a lack of rainfall recently.
Explanation: From looking at my graph I can see that there was no water in this section of the river. I can also tell that the river did not meander at this point. As it is not shallow at one side, and moreover it is no deeper, meaning that there will be no faster point of the river. The depth of the river also doesn’t reach 0 cm until it reaches the edge, which shows that there are no river beaches/ point bars which are found on a meander. The graph also shows us that the river is not particularly deep, as the deepest part is 70cm, and the shallowest is 0cm.
I believe that there was a very small amount of river in the river because it has either been a very dry summer, which would mean that much of the water had evaporated, and moreover there would have been limited rainfall, thus meaning that the rivers water would not have been refreshed. However there are signs of water being in the river, the picture shows that erosion has been occurring on one side of the river. On the other side a river beach has been formed, which is where the river has meandered with the faster water flowing on the outside and the slower water flowing on the inside, eventually stones are deposited by the slower water, and it dries up and forms a river beach. The reason that there is no water is because the river is seasonal, in winter the source of the river will be flowing freely, as it is colder and there is a higher rate of rainfall. Whereas in summer when it is drier there is less rainfall resulting in a far lesser volume of water flowing down the river. The maximum depth of the river channel is 70cm, this shows that the maximum depth of the river water could be 70cm, otherwise the river would overflow.
Site 2- Millyford Bridge
Description: From looking at my graph we can establish that at this section of the river there is water; furthermore we can tell that the river is deeper than at site 1, as the depth at site 1 was only 70cm, whereas at this site it is 1.20m. This could be due to more vertical erosion, or the river carrying a larger bedload, and as a result of traction the boulders and stones will wear away the sediment on the bottom of the river. From the graph we can also tell that it is meandering to the right. As a river cliff is forming on the right hand side of the graph, and a point bar is forming on the left. We can tell that a river cliff is forming as it is straight edged on the right, and furthermore it becomes shallower on the left, and as I imagine that it is where the slower water flows, and rocks and stones have been deposited there.
Explanation: The above graph shows the river further downstream, we can tell this by the fact that here there is a river channel, and it is deeper and wider than that of source 1. There is also a large drop about one metre from the river bank on the right. From this we can tell that there has been a large amount of lateral erosion, as there has been a large increase in the width of the river channel, as at the source it was 2 metres, whereas now it is over 4 metres wide. Corrosion has also taken place, as the river is carrying a larger bedload, therefore larger rocks are wearing away more of the riverbed, this makes it deeper on the bed. The right hand river channel almost certainly has a point bar, as it is less deep, and it is quite shallow. This could be where the slower water could be flowing round a bend (meander), as the faster water will flow along the outside in the deeper water. Also in this area there were plenty of meanders, so it would probably be true that the river meanders here. The river also shows a river cliff on the left hand side, we can see that there is a river cliff there because it falls steeply into the river channel.
Site 3- Balmer Lawn
Description: The above graph shows the left hand side of the river to be the deeper side, with a maximum depth of 45cm; the right hand side of the graph is very shallow, where the depth is 1 or 2 centimetres for over 4 meters. The scale of the graph is also much larger than the other 2 sites visited, which shows it is very wide at this site.
Explanation: Balmer Lawn was the widest section of river we visited, at its widest it was 14 meters in diameter, however as shown by the above graph it was very shallow in comparison to site 2. However despite the river was very wide, it had a comparatively small depth. The 4m to the right of the river channel was only approximately 1cm deep, this is because a large bedload was deposited, and the slower water flows here. On the left hand side of the graph the deeper and faster water flows, this suggests that there will be a meander, as there is a point bar on the right and the river cliffs are on the left. The meander would therefore be right.
Conclusion
From conducting our river study we can prove that many of my hypothesis I made were correct. We can tell this by a number of things shown above in the results section. For instance that hypothesis 1 was correct, we can see this by the fact that the width of the river increased by 10.8m. As at its source it was 3.40 in width, whereas it ended up with a large width of 14 meters. My second hypothesis was proved incorrect, as I predicted that it would become deeper downstream, however it became very shallow in parts of site 3, I believe it to be because of the fact that it became so wide that not as much attrition or vertical erosion was taking place. As the water has such a wide river channel that it flows freely, and when we were at site 3 there was a large point bar, so it was slowly meandering causing all the stones to be deposited so less attrition occurs.
My hypothesis number 3 was proved correct, as the speed of the river increased. We can tell this by the fact that at every site we tested the river for its velocity. This involved measuring out a distance (which was kept equal for accuracy purposes on every test) and timing how long it took a dog biscuit to be carried from the start to the end of the course in a certain amount of time. We would then repeat the experiment a number of times for accuracy. We discovered that it took less time for the river to carry the dog biscuit over the distance further downstream. Which shows the river is flowing faster (a larger velocity) further downstream. For my fourth hypothesis
Evaluation
I feel that my conclusions are accurate, as when we conducted the River study we did a number of things to make sure it was accurate. For example when we tested the velocity of the river we would measure the start and the finish distance, and ensure that all factors were kept the same to make sure of no anonymous results. We would also repeat the experiment 3 times, to make sure that we get the most accurate results possible. When we measured the width and depth to make it fair we would repeat the depth test, and record all results taken accurately in a table, which would make sure that it is not forgotten or changed.
The only downside to collecting data was at site 1. This area had no water; so collecting the bedload was difficult, as it was hard to distinguish the river channels bedload from the stones that had gathered there from wind and human activity. This affected my results by making the bedload vary so greatly that it is hard to gain an accurate result. I believe that the bedload would have been smallest at stage one, as the river was not yet powerful enough to transport larger rocks.
The other problems encountered were the fact that we only went to the site at one time of year. This meant that during other times of year the rivers characteristics would have varied greatly from that of summer. For example I believe that if we visited the site in winter then it would have water in, as in winter there tends to be higher rainfall, which means that the river channel would fill up. Moreover it tends to be colder, which means that the water will not evaporate and therefore the water will remain in the river for a longer period of time.