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The river Gwaun: Investigating how the course of the river changes from the source to the mouth.

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Introduction

Introduction I am investigating how the course of the river changes from the source to the mouth. I will study the River Gwaun at 4 sites, starting at Gellifawr (near the source), then going to Pontfaen, then Llanychaer, then finally ending at Lower Fishguard, near the mouth where the river meets the Irish Sea. I went to do my fieldwork on the 20th May 2002 with my Geography class and another from my year. I was in a group of 5, with Richard Gledh�ll, Chr�s Strzeleck�, Jason Inglesant. Ashley Stone and James O'Shea. We worked in a group because it is the easiest and probably the only way to collect all the data we need at each site. We collected data from each of the 4 sites. Site 1 - Gellifawr This is close to the source and is situated in the Preseli Hills. The relief is steep and the banks are V-shaped, typical of parts of the river in the Upper Profile. The water and the banks are very muddy. The river was apparently flowing slowly, there was a lot of large, angular bed load and there was a few small waterfalls. There was evidence of turbulence at some parts of the river. Site 2 - Pontfaen This site was on a floodplain next to a farm. There was evidence of an ox-bow lake nearby, which shows the river had been meandering. The river is flowing quite fast and the bed load is mostly small sub-angular/rounded pebbles. The river is quite wide and had much clearer water than Site 1. The riverbanks were flat but there was an overhang. There was some evidence of man-management as there were big boulders on one side of the river (the side bordering the farm), which is presumably to stop eroding on to farmland and the small pebbles covered the bed to stop erosion and making the river deeper. ...read more.

Middle

15.82 25.37 18.154 All speeds in seconds Averages The average speed for each site is: Site 1 - 37.554 seconds Site 2 - 25.542 seconds Site 3 - 13.442 seconds Site 4 - 18.154 seconds Graphs Description The results show that the speed of flow increases from Site 1 to Site 3 but then decreases at Site 4. Part of this is due to erosion; part is due to human interference. In Site1, the bed load largely influences the speed. The bed load is mostly large and angular and the slowest speed of flow we recorded (1min5seconds - 2nd speed measured at Site 1) was so long because it was caught by bed load and had to be loosened otherwise it would have been void. In Site 2, the entire bed load was (evenly) spread out over the riverbed and was mainly small (round) pebbles. This had little effect on the speed. In Site 3, the bed load was inconsistent in size and shape and did not have a (big) impact on the speed of flow. In Site 4, the river had been modified so the speed of flow was fast (therefore less deposition at the riverbanks/on the riverbed which decreases the risk of flooding) but it was slower than Site 3 because it was at the mouth of the river so was beginning to slow down, because of the human interference and because most of the bed load is large to stop erosion and spread out along the riverbed to minimise flood risk. Discharge Hypothesis I predict the river discharge will increase from Gellifawr to Lower Fishguard. I think this because discharge = length x width x speed, and if they all increase like I predict, then the discharge would then subsequently increase. I will only use the average discharge because it is the most accurate/even/fair discharge and it gets complicated when deciding and justifying which speed goes with which width and which depth, etc. ...read more.

Conclusion

wrong were taken to either avoid or minimalise the damage caused by such events. Some decisions on methods can also change the outcome of an investigation; how many sites to go to? How many widths/depths/etc. should be recorded? How many repetitions should be done? Etc. Most of these factors are down to how much time you have to do your investigation. I couldn't do 10 widths and 10 repetitions or have 50 bed load or go to 12 sites, etc. because I was only at each site for 45 minutes and there would be no time for other things. Another important decision is to decide when to go. In summer there is less rainfall so the depth is lower than in winter, which can affect the discharge, speed and width, as well as speed, which then affects the hydraulic power and erosion levels. The field trip I went on was in June, but it was postponed twice because of torrential rain making it dangerous to work in, so the climate also affects the results. However, a lot of my predictions made in the hypotheses sections of each aspect measured were correct, or correct in parts. The ones that were not correct, particularly bed load and speed in Site 4, was because of human intervention and I believe that, had the river run its natural course, would be correct. I did successfully fulfil my aims, which were to investigate the changes in the river Gwaun as it goes from source to mouth and I have documented it well. Overall I am happy with my set of results. I believe that all of the results that were odd and other things that went wrong were unavoidable and it might have balanced out the conditions with other times of the year. Any errors with the results would be natural as they are never going to be perfect, especially if the methods are not done with top-of-the-range equipment and technology that professionals use. Geography Coursework: River Gwaun Fieldwork 2002 Liam Barnes 11o Candidate Number 1867 ...read more.

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