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An Investigation of Channel and Stream Characteristics For Streams on the Isle of Arran

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Introduction

An Investigation of Channel and Stream Characteristics For Streams on the Isle of Arran Aims To investigate hypothesis associated with increasing distance down stream for streams on the Isle of Arron. Objectives To set up and test hypothesis To investigate how channel characteristics change with increasing stream order. Hypothesis 1. As the river progresses downstream the bedload decreases in size. 2. The bedload becomes rounder in shape downsream. 3. The width will increase in size as the river goes downstream towards the mouth of the river. 4. The velocity of the river will decrease as it goes downstream. 5. The depth will increase in size as it goes downstream. 6. The discharge will also increase as it goes downstream. Theory There are three processes by which material is transported from land to the sea (via rivers) these are: i) Weathering-physical and chemical breakdown of rocks. ii) The slope-the products of wethering are moved down the gravity gradient in mass movements by the slope wash processes. iii) Fluid transfer-water, air and ice. The load, carried by natural streams, can be separated into three compounds. The material carried by the river is called the rivers load. It comes from river erosion and weathering of the river banks. Especially when the river is bankfull, considerable quantities of load can be carried. The total amount of load that a river can carry is called its capacity. The greatest size of material it can transport is called its conference. Load is transported in the following compounds: 1. as dissolved load-material is transported in suspension, this is the chemically dissolved rock. 2. as wash load-fine particles move steadily in suspension (fine mud floating in the water). 3. as bed-material load-material is transported in saltation. This is coarse sand and small pebbles bouncing along the river bed. Bed material also moves in traction which is when large boulders trundle along using smaller stones as ball bearings. ...read more.

Middle

These enable one to compare easily and quickly the number of pebbles of each shape that were collected at each site. I found that this method enables me to clearly appreciate the number of pebbles of each different shape at each site separately but it was not so good when comparing the sites with one another. I then tried to use another graphical method to display this more clearly. I drew eight bar charts next to one another and found that by shading all the discs in one colour, all the rods in another, I was able to see clearly any trends in number over all eight sites. Athough this method was clear I thought that if I drew a line graph, one line for the number of discs at each site, another line for blades, and so on, it may be easier to spot the patterns. RESULTS OF THE VELOCITY OF THE RIVER AT EACH OF THE SITES Site one - 33.76 cm/s Site two - 15.58 cm/s Site three - 159.68 cm/s Site four - 74.08 cm/s Site five - 12.32 cm/s Site six - 31.68 cm/s Site seven - 12.92 cm/s Site eight - 20.25 cm/s RESULTS OF THE WIDTH OF THE RIVER AT EACH OF THE SITES Site one - 1.49m Site two - 4.6m Site three - 4.87m Site four - 5.90m Site five - 7m Site six - 7.6m Site seven - 7.2m Site eight - 8.6m RESULTS OF THE DEPTH OF THE RIVER AT EACH OF THE SITES Site one - 4.52 cm Site two - 12.25 cm Site three - 11.09 cm Site four - 21.73 cm Site five - 6.86 cm Site six - 2.55 cm Site seven - 11.73 cm Site eight - 17.55 cm RESULTS OF THE BEDLOAD SIZE (LENGTH OF B-AXIS) AT EACH OF THE SITES Site one - 10.60 cm Site two - 5.77 cm Site three - 20.59 cm Site four - 12.02 cm Site five - 16.82 cm Site ...read more.

Conclusion

This is quite possible although there is no reason why I should have been more biased at site four than at any of the other sites. Another possible explanation is that bed material is generally better sorted with distance downstream although tributary inflow can disrupt the picture. I have considered various explanations why site four did not follow the pattern of the others. Without further tests I am unable to give any definite reasons. Conclusion My first hypothesis was that as the river progressed downstream the bedload decreased in size. I proved that this hypothesis was in fact correct. I found that the average length of the b-axis decreased downstream.This meant that the pebbles became smaller. This showed clearly that the size of the pebbles decreased downstream. My second hypothesis was that bedload becomes rounder downstream. This was not really proved or disproved because it was found that discs and spheres which are both round shapes (compared with rods and blades which are long and thin) dominated the bedload for all eight sites and did not really increase or decrease dramatically at either end of the river. I found out that there was no relationship between the geology of the land and the results I collected. I also found that on this occasion the velocity of the river did not directly affect the size and shape of the bedload. Criticisms From other research investigated I would have expected my hypothesis to have been proved correct. This was not conclusive. Any number of the following could explain why this is so. * My hypothesis could have been wrong. * My methods or measurements may have been inaccurate. The measuring equipment may have led to inaccuracy. * We may have visited exceptional sites. In addition, I was unable to find sufficient explanations indicating why such results were obtained. I would have liked the opportunity to have returned to Isle of Arran to check these results which were out of line with the other, in particular site four. ...read more.

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