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Geography Coursework: Epping Forest

Extracts from this document...

Introduction

Abstract This is a study of the changes in river processes along the long profile of a river. To study this we will use a sample river. The river the study will be based on Loughton Brook, which is a river situated in Epping Forest in Essex and is also a tributary of the river Thames. A journey will be made to the river and measurements will be made at three different sites. The measurements that were taken will be studied so conclusions can be made about the changes to characteristics of a river with distance downstream. Aims and Hypotheses The overall aim of this study is to investigate the changes in river characteristics downstream along Loughton Brook. To investigate these changes in more detail a range of hypotheses will be tested. These hypotheses are: 1. The width of the river channel will increase with distance downstream. I expect to find this because in the long profile of a river channel width increases. This is because there is a greater volume of water at a faster velocity. This causes more hydraulic power erosion in the river channel downstream, which makes the channel wider. 2. The depth of the river channel will increase with distance downstream. I am expecting to find this because as the velocity of the river increase further downstream there will be more hydraulic power erosion which will cause the river to become deeper. 3. The wetted perimeter increases with distance downstream. This is because I expect the depth and width increase so the wetted perimeter must also increase. 4. The gradient will decrease with distance downstream. I expect to find this because in the long profile of a river the further downstream along the river the less high the river is above its base level. 5. The velocity increases with distance downstream. I expect to find this because as the river flows downstream there will be a larger volume of water. ...read more.

Middle

We then used the roundness and sphericity index, which we were given at the field centre, to see how round and smooth each pebble was and then measured the pebbles at their longest point to find if the shape changed downstream. The roundness index was not very accurate because the results were based on someone's opinion and not on a proper measurement. Also only a very small sample of pebbles were taken and these may not necessarily be representative of the all the pebbles at the site. Channel Cross Section Diagram - Site 1 Depth was measured at three points across the river channel, at 1/4, half way and 3/4 of the distance across the river. Therefore, to produce the cross section, the points plotted on the Average Channel Width axis needed to be calculated with this method: Average channel width (m) = 3.5 = 0.875m 4 4 Hydraulic Radius This calculation shows the efficiency of the river channel and is measured in metres. The larger the Hydraulic Radius the faster the flow of the river therefore the river more is efficient. Hydraulic radius is calculated using this method: Hydraulic Radius = Cross-sectional Area (m2) = 0.11 = 0.120m Wetted Perimeter (m) 0.91 Channel Cross Section Diagram - Site 2 Depth was measured at three points across the river channel, at 1/4, half way and 3/4 of the distance across the river. Therefore, to produce the cross section, the points plotted on the Average Channel Width axis needed to be calculated with this method: Average channel width (m) = 3.4 = 0.875m 4 4 Hydraulic Radius This calculation shows the efficiency of the river channel and is measured in metres. The larger the Hydraulic Radius the faster the flow of the river therefore the river more is efficient. Hydraulic radius is calculated using this method: Hydraulic Radius = Cross-sectional Area (m2) = 0.12 = 0.128m Wetted Perimeter (m) ...read more.

Conclusion

Show Pebble Roundness and Sphericity The Pictogram shows clearly that the pebbles collected at Site 1 are more angular than at Site 3. At Site 1 there are mostly angular pebbles and very few rounder ones but at Site 3 there are mostly rounded pebbles but no angular pebbles. The chart shows that at Site 1 there are three very angular pebbles, two sub rounded pebbles and only one well-rounded pebble. The pebbles collected at Site 2 are rounder than at Site 1 because there are no very angular pebbles, three sub rounded and three well-rounded pebbles. At Site 3 there are no angular pebbles, three sub rounded pebbles and three well-rounded pebbles. This is evidence for the hypothesis that the bed load shape (roundness and smoothness) should increase with distance downstream. Graphs 12, 13 and 14 - Cumulative Frequency Curve of Pebble Long Axis From these cumulative frequency curves the approximate median length of the pebbles can be found. This can be used to compare the data for the pebble length more easily. Graph 12 shows the cumulative frequency curve for the long axis of the pebbles at Site 1. At Site 1 the approximate median long axis length is 2.35cm. Graph 13 is the cumulative frequency curve for Site 2 and it shows that the estimated median long axis length is 3.6cm. This is longer than the median for Site 1 by 1.25cm. The last cumulative frequency curve is for Site 3 and this from this graph the approximate median length is 2.4cm. This is longer than Site 1 by 0.5cm but shorter than the pebbles at Site 2 by 1.2cm. Overall the pebbles at Site 1 are shorter than the pebbles at Site 3 but only by 0.5cm. The pebbles At Site 2 are the longest at 3.6cm although there may be an anomaly. This may be the reason that the results that were obtained do not entirely follow the hypothesis that the bed load size will decrease with distance downstream. ...read more.

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