Investigating the river Caerfanell

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AS GEOGRAPHY COURSEWORK                                        STEPHANIE ADU

INTRODUCTION

I am going to be investigating the river Caerfanell. This river is a right-bank tributary of the River Usk of whose source is in the eastern end of the Brecon Beacons national park in South Wales, and joins the main river further downstream of Brecon.

The catchment area is 32.4 km2 and is an area of high precipitation, with 1800- 2000mm/year on average falling near the source and 1100mm/year near the confluence with the Usk. The valley of the Caerfanell lies within the Brecon Beacons national park and is relatively untouched except in more recent years where the river has attracted many holiday homes to situate nearby having an impact on surface runoff. The surrounding forest trees are coniferous and mostly evergreen, which also have an impact on runoff through interception and evapo-transpiration. A reservoir (the Talybont reservoir) was built in 1937 to store water, and now is being used as a drinking water supply for surrounding areas. The river has a built a delta, where it enters the reservoir, and just above the delta, the river has a strong tendency to meander eroding the farmland either side, although the farmer has attempted several times to straighten the river to protect his livestock.

The Caerfanell valley has been carved into sedimentary rocks of the Devonian age (about 360 million years ago). These are known as the old red sandstone, which consists of a thick sequence of relatively resistant sandstones with easily friable and erodable mudstones. Also the acidity of water caused by the coniferous trees helps erode the mudstone. This modification of the sand and mudstones has made a series of attractive waterfalls in areas such as Blaen y Glynn.

During the Pleistocene there was an ice cap on the Brecon Beacons with valley glaciers descending from it along the Caerfanell. The ice left behind glacial troughs (steep sided U-shaped valleys).

Within the ten thousand years since the ice melted, the Caerfanell and its tributaries have begun to alter the glacial landscape, creating in places steep v-shaped valleys and re-worked glacial deposits with some sediments still carrying its glacial origin.

I chose three sites on the river Caerfanell, to perform my methods.

Site 1  Blaen - y- Glynn

Site 2  Pont blaen y Glyn - The Valley

Site 3 By the Talybont reservoir.

These sites are situated on the location maps later in my project.

My main focus of these coursework is to answer the following question…

“Is there a correlation between velocity, gradient, and channel shape?”

I intend to answer this question through a series of key questions.

  1. How does velocity change downstream?
  2. How does channel shape change downstream?
  3. How does the channel shape affect velocity?
  4. Does gradient affect velocity?
  5. Does gradient affect channel shape or roughness?    

My hypothesis’ are:

  • Velocity increases downstream
  • Channel shape increases in both width and depth downstream
  • As channel size increases, velocity will increase
  • As gradient increases, velocity will increase
  • Gradient will have no affect channel shape or roughness

METHODOLOGY

The three sites we choose from this river to assemble and gather results from are…

Site 1 - Blaen y Glyn is a section of this river very close to the source, 400m above sea level.

Site 2 - Pont blaen y Glyn is an area further down the valley, near the middle of the river, 260m above sea level.

Site 3 - Talybont reservoir delta is a section, which is near to the mouth of the river, 190m above sea level.

We choose to perform the experiments and gather evidence from these 3 contrasting areas of the river moving downstream to gather a holistic view of the rivers characteristics. This increases the accuracy of my results, as they are not bias whilst trying to represent the whole river.

Also by choosing 3 different areas, I will be able to analysis the different processes and features that a river can present downstream therefore gathering a background of the rivers history.


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DATA ANAYLSIS

Velocities against Cross sectional area of river.

The trend above occurred because as the cross sectional area increases, the area of which there is minimal friction between the water, riverbed and surface increases. This limit in friction increases velocity as velocity can occur more easily and more efficiently.

The anomalies on this graph is situated at…

Site 1 – The velocity reading is higher than expected at 0.527 m/sec, with a C.S.A reading of 0.2m2 

Suggested reasons for this anomaly (although naturally upstream the water ...

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