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How does the Efficiency and Cross-Sectional Area of a River Change Down Stream?

Extracts from this document...

Introduction

How does the Efficiency and Cross-Sectional Area of a River Change Down Stream? For my investigation I will be looking at the cross-sectional area of a river and how this affects efficiency in the river of Little Beck as the stream moves downstream from the source to nearer the mouth. To do this I will be taking measurements of the cross sectional area and the efficiency at 12 different sites along the river (See fig. 2 for map of river and 12 sites). The source of May Beck is approximately at a height of 280m on Fylingdales Moor in the North Yorkshire Moor National Park. The river flows south to join the Parsley beck, and the combined flow of these two rivers, now called the Little Beck, becomes tributary of the much larger river, River Esk, which reaches the sea at Whitby. During my investigation, I will be comparing my results to that of the Bradshaw Model. The Bradshaw Model is a model of an ideal stream (see fig. 1). By using this I can compare my results with the model to see how ideal Little Beck is. According to the Bradshaw model, at the source of the stream the cross-sectional area and efficiency are low at the source but as you move down stream they increase. Three key questions I have constructed to help me with my investigation are: 1. How does efficiency change as you go down stream compared to the predictions of the Bradshaw Model? 2. How does cross-sectional area vary from sites 1 to 12 compared to the predictions of the Bradshaw Model? 3. Is there a pattern in the data of the efficiency and cross sectional-area? Methodology Table This methodology table shows all the types of data I collected, why and how they were collected. In order to investigate into cross-sectional area and efficiency I will not need all this data, so I have highlighted the methods in green which I will need to use to carry out my investigation. ...read more.

Middle

above, overall there is a positive correlation. With increasing cross-sectional area the hydraulic radius does increase. This is shown by the line of best fit. All points follow an obvious trend, showing no anomalies in the graph. We can see from the data above that the efficiency and cross-sectional area increases, but this should also mean that the velocity of the river increases also. In graph 5 we can see that there is a negative correlation from the line of best fit. The average speed at site 7 and 8 is higher than expected, making it a positive anomaly. The average speed at site 11 is lower than expected, making it a negative anomaly. This could be due to foliage catching the biscuit used, stopping it from flowing down stream efficiently, or the biscuit may have been lost under the current of the river. These results aren't very reliable due to the method we used to collect the data. To show that velocity increases with hydraulic radius I have produced a scatter graph, which can be seen to the right (graph 6). As can be seen there is a positive correlation, but several positive and negative anomalies are present. These anomalies are mainly results with a hydraulic radius between 2 and 3, and a low velocity between 10 and 30 seconds. This will have been due to the same reason the velocity graph is inaccurate. My graphs show quite good correlations between the data, but there are some strong positive and negative anomalies. To get a clearer source of correlation data, I will produce a Spearman's rank correlation coefficient. If two sets of data correlate exactly, they are said to have a perfect correlation. If one set of values goes up as the other set goes up, a perfect correlation is found, which would have the Rs value of 1.0. A perfect negative correlation (as one set of data goes up, the other goes down) ...read more.

Conclusion

If I were to repeat this investigation, I would perhaps increase the number of sites where data was collected so I could strengthen my finding, perhaps more sites closer to the mouth as we weren't very close to the mouth, or maybe do the same tests in another river so I could compare the two rivers results. To collect the data needed for my investigation, there were several methods I needed to carry out (to see what data was needed to be collected and what methods were used, see figure 3 on pages 3). These included measuring the velocity and stream surveys looking at the width and depth of the river. I feel the method used to measure the width and depth worked well and was done successfully, but perhaps more intervals could have been taken to give a stronger set of results. Graphs were produced to show the cross section of each site we visited, which can be seen on page 7 and 8, graphs 2A to 2L. These shown the shape of the river well, however they aren't very reliable as the width hasn't be used on the x axis, not showing an accurate cross-section. By collecting this data, I was able to calculate the hydraulic radius of the river which would tell me how efficient a river was using a particular method (see pages 8-10, 11-12), which gave an accurate and reliable result. To measure the velocity, a dog biscuit was thrown into the stream at each site; this method wasn't very effective and gave inaccurate results. This was due to foliage catching the biscuit thus stopping it from flowing efficiently, or the biscuit could have gotten lost under the currents. If I were to repeat this, I would have employed a better method by using a flow metre and collected more data to give a more reliable set of data. Although some of the methods used didn't give accurate results, I was able to answer the question to my investigation, making the trip and methods successful. ?? ?? ?? ?? Matthew Southward Geography: Personal Investigation 1 ...read more.

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