issues with my results and conclusions. My hypothesis would have been answered correctly, and may well have given me a different outcome. More measurements could have been taken, ensuring a greater accuracy.
The second hypothesis stated that cross sectional area of a river increases downstream. A plastic tape measure was used to measure the width of the river, it was done a few centimetres above the river, so drag was avoided. However, there were problems. The day that I measured the River Bourne, it was very windy, this meant that it was difficult to make sure that the tape measure was straight all of the way across. If the tape measure was even slightly bent (or not exactly straight) then the results would be incorrect, as the width would increase. Also, the entire width needed to be measured. However, I may not have seen every single overhang. Therefore, I would not be measuring the exact width of the river, and the result would be shorter than the actual width, therefore making my results wrong. I could have improved these methods, by using a metal tape measure instead of the plastic one, which would not have bent in the wind. I could have checked more carefully for overhangs. These methods would have given me results which were close to their true value, and would have proven if the hypothesis was correct or not. I was measuring at the most convenient spot for myself, this may not actually have been the best place. The depth of the river was measured using a metre rule. On the whole I thought this was well done, as the precautions taken worked well. The metre rule was used by the same person, and therefore pushed down by the same force. I ensured that the metre rule was perpendicular to the riverbed, and that it was pushed in sideways, so as not to create a large amount of resistance from the water. Not a lot could have been done to improve the methods used to measure the depth of the river. However, perhaps I could have done a pilot study. This would have ensured that the sites I had chosen typified that stretch of river. This would have made my results and conclusions more reliable.
The third hypothesis which I measured stated that the bedload of a river gets smaller and smoother downstream. To measure the size of the bedload, callipers were used to measure the length, width and height of the pebbles. Also, the volume of the pebbles was recorded using a displacement method. The shape of the pebbles was measured using a power scale of roundness. For this hypothesis I believe that my methods were very good, and not much could be done to improve them. Callipers are a good way to measure pebbles, they are easy to use, and far more accurate than a ruler. The displacement water method is a good way to measure the volume of the pebble. However, with this, mistakes can easily be made. One can accidentally put other items from the river into the beaker with the pebble by accident. Also, when the pebbles are very small, this method is crude. The beaker is not very precise, it does not measure to a great deal of detail, and more than one small pebble can accidentally be placed in the beaker. It is hard to read a very small change in volume displaced. To improve this, I could have used a measuring cylinder, for the very small pebbles, and for the larger pebbles, use a beaker which measured to
a greater degree of accuracy. The picking up of the bedload was not random enough, and I only selected the bedload which was nearest to the bank, this was therefore the easiest to access. The method to measure the scale of roundness, is a very common, and on the whole, foolproof method of measuring the shape of pebbles. However, as a large quantity of pebbles was measured, mistakes could have been made in the writing down of the number or the category which the pebble falls into. This is entirely a human area, but would still have affected my results the same as the other reasons outlined above. This could have lead me to conclude wrongly about the hypothesis.
My fourth hypothesis stated that channel efficiency of a river increases downstream. Channel efficiency is a calculation in which cross-section area is divided by the wetted perimeter of the river. My evaluation for measuring cross-section area is shown on page ... . This shows all of the problems with my methods, and how they could have been fixed, and they all are applicable here. The second measurement is wetted perimeter. This was measured by putting a metal chain on the river bed, and measuring its length which was in contact with the perimeter of the river (its banks and bed only). This method is simple and mainly foolproof, but the problem is that the chain does not always stay on the river bed, and does not always cover all of it. This affects my results, because a smaller length is given than what the true measurement, and this will therefore affect my conclusion for this hypothesis, because, I do not know what the true wetted perimeter is, and therefore can not accept or reject my hypothesis.
My fifth and final hypothesis is that discharge of the river increases downstream. Discharge is purely a calculation and is calculated by multiplying velocity and cross-section area. My evaluation for velocity is on page ..., and my evaluation for cross-section area is on page ... . The reasons for these evaluations are all applicable to this one.
Overall, I think that my study of the River Bourne was accurate, but I feel that it may not have been the best river to study. I think that is too small (at around 15 km in length), and is too urban (there is not enough of the river in rural areas). As the river was small, this would have affected my hypotheses. This would be because processes such as attrition would not have enough time to erode pebbles. Being an urban river is a problem, because the bedload could be affected by rubbish dumped into the river (I saw a lot of rubbish in the river, such as computers, cables, paperwork and even needles) and also affect results on river depth and silt depth. Therefore, the conclusions I have drawn from my studies are not valid on all rivers, it is not possible to automatically assume that the results for the tests will be the same on a much larger river, such as the Nile or the Amazon. However, the most greatly affected hypothesis was discharge. Any tributaries flowing into the River Bourne would have a profound affect on our results, as the river does not carry much
water. The drainage basin of this river is a lot smaller, so hardly any water is 'caught' compared to a larger river. My river was only a low land river; it can not be compared to an upland river. It is important to note that you can not assume that the conclusions will be the same. The River Bourne is so small it does not have a proper middle and upper course. Also, as I did not do a pilot study, and only measured the river once in the summer, my results and conclusions could be affected. I went during the summer, where the river would be smaller than normal, as processes such as evaporation would have affected the volume of water in the river. This would have affected all of my hypotheses. Perhaps I should have measured the river at another time in the year. Finally, not all of my hypotheses were actual measurements, some were calculations. I could have actually measured the wetted perimeter for example.
