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To find out how channel characteristics such as width, depth, area, efficiency, gradient and bedload change downstream

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Introduction

1.0 Introduction Aims 1. To find out how channel characteristics such as width, depth, area, efficiency, gradient and bedload change downstream? 2. To find out how flow characteristics, such as velocity and discharge change downstream? Having studied rivers to a great extent at GCSE and A level I have decided to carry out a study on river processes and characteristics. I have chosen the River Brett as the location for my study due to its large drainage basin and varying stream orders, enabling me to carry out a wide ranging investigation. The River Brett is a tributary off the river Stour in Suffolk. The river Brett's total length is 100 km. Hypotheses I plan to investigate the following Hypotheses: 1) All of the river dimensions will increase downstream e.g. width, depth, area and hydraulic radius. 2) All of the flow characteristics will increase downstream such as velocity and discharge. 3) Bedload size will decrease and bedload shape will become smaller and rounder downstream. Explanation of Hypotheses I would expect the channel dimensions to increase downstream due to erosion of the riverbed and banks. Due to abrasion the width and depth would increase as material being carried down the river would rub against the bed and banks causing them to erode away. This in turn would cause the flow characters to increase due to there being a wider and deeper area for the water to flow through. I would expect the bedload size to decrease and the shape to become smoother and rounder downstream due to the process of attrition. As the material travels downstream it rubs against each other therefore becoming smoother and rounder. Background and Theory of river processes 1. Hydrological Cycle 2. River Processes - Erosion Deposition Transportation 3. Other Factors affecting a river Erosional Processes Erosion is a process whereby material carried by the river wears away the bed and banks. ...read more.

Middle

We all wore wellies and tried to avoid the hanging branches. Evaluation of Methodology As my investigation is of a physical nature, a majority of the data that I collected was primary. This was an advantage, in one perspective, as I knew that all my data was true, but a disadvantage as it is hard to get a 100% accurate result. There were a number things I had to do in order to gain more accurate results. 1) Make sure that the measuring tape was taut when measuring river dimensions. 2) When collecting the bedload stones, make sure they were all of a varying size and from along the width of the river. This would insure I didn't get a biased result. 3) Making sure, when measuring the depth that I didn't place the metre stick on a big boulder, that was uncharacteristic of that part of the river. 4) Appreciate that the flow metre needed a certain minimum depth in order to take an accurate reading. Also not standing in the way of the flow to the flow metre, decreasing the velocity of the water to the flowmetre. 4.0 Analysis Method of analysis To find the relationship between the characteristics of a river and the distance down stream I am going to use two methods to analyse my results. Firstly I will present my data graphically using line graphs, and look for patterns and correlation's within and between sets of data. Secondly I will interpret my results by calculating the Spearmans' Rank Correlation Coefficient. * Line Graph A line graph can be made by plotting each pair of data as a single point on the graph. The points are then joined up to make a line. By studying these plotted points I can see if there are any correlation's between the river characteristics and the length of the river. If the points lie close and with a positive gradient, this suggests that there is a positive or direct correlation between the two sets of data. ...read more.

Conclusion

The discharge increases due to the increase in velocity and cross sectional area which occur further the downstream you go. The discharge also increase's due to the increase in stream order i.e more tributaries have joined the river and therefore contributing to the flow. The increase in velocity is due to a number of factors: gradient (relief of land), efficiency of river (roughness of channel) and cross sectional area. The steeper the gradient the faster the water is going to flow. The gradient lessens closer to the mouth so the velocity should decrease, however the channel efficiency increases (the bed and banks become more smooth) so there is less friction and therefore water is allowed to flow faster. My third hypothesis stated that 'Bedload size will decrease and bedload shape will become smoother and rounder downstream.' My results for bedload size have contradicted my hypothesis, as my results showed that bedload size overall increased downstream, however there was a very weak correlation showing this. Bedload shape however did become smoother and rounder downstream supporting one of my bedload hypotheses. The fact that bedload size doesn't change but shape does, could be due to the geology of the land, as glacial morraine is a hard rock and is not easilty eroded, however attrition would have been able to smooth rough edges but not erode the material enough to decrease the size. In conclusion I can say that the majority of my hypotheses were true. Evaluation My results were fairly accurate but there are some factors that need to be taken into consideration which could have altered the results. Firstly, the weather. It was very dry and hadn't rained for some time. The river was very low so this could have made the velocity uncharacteristically slow. Also there was people standing in the river, which could have caused more friction, and therefore the velocity would have decreased. Some of the sites were surrounded by trees, being autumn when the investigation was carried out, leaves may have fallen into the river causing an obstruction to the flow ...read more.

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