Do the Characteristics of a river change downstream?

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James Black

Geography Coursework

Year’s 10 and 11

Do the Characteristics of a river change downstream?

Summer 2003

James black

Section 1 - Introduction

During this investigation, we aim to find out how the River Wharfe’s characteristics change from its source to its middle course. Some of these characteristics are of course physical such as the width and depth of the river, the lithology of the bedload and so on, others are affected by human influence such as the type of bedload, and land use either side of the river valley.

I have decided to choose the examples of Backstone Beck and the River Wharfe to see if the knowledge that I have gained in lessons concerning the theory of rivers applies to these real life examples.

I have chosen to study the River Wharfe because not only is it one of the major rivers in Northern England but also flows through Ilkely, near our school meaning accessibility is not a problem. The site at which we will be conducting our experiments is far away enough from the source that it demonstrates the lower/middle course of the river. It also has little human influence making it relatively natural.

I have selected to study Backstone Back since it is a tributary of the River Wharfe and therefore more accessible than the source. It is also a good representation of the upper course and should provide me with good contrasting results. We are not able to study the absolute source of the River Wharfe, as it would prove difficult and expensive to get there. Taking this into consideration Backstone Beck was a good choice as the results we would have gained from each location we deducted to be quite similar.

Both Backstone Beck and the River Wharfe flow through Ilkley as is visible on Appendix 6. Ilkley lies in the heart of the Yorkshire dales which in turn is in West Yorkshire. The follow on of maps from the original map of Britain shows where the two sites are in relation to other places in Britain. The purpose this serves is to give a precise location of each site and an exact idea of how far away from each other they are. Appendix 4 locates the two sites of Backstone Beck and the River Wharfe and where they are in relation to height. Appendix 3 shows the catchment area of the River Wharfe and its approximated area.

Backstone Beck – The upper course of the river.

Backstone Beck begins at grid reference 126460 and ends at 127483. Although the path taken by Backstone Beck is not completely straight it is neither particularly winding. There are a few large bends around interlocking spurs but most of the other bends in the beck are insignificant. The river runs down a moderately steep sloping gradient for 1km or so towards the River Wharfe then goes on to a somewhat gentler slope for the remainder. This is apparent by the way the contours are grouped together on the map (appendix 4.) The altitude at the source of Backstone Beck is approximately 315m above sea level. The level at which the beck meets the river is roughly 100m above sea level.

The site at Backstone Beck where we will be collecting our data is roughly to the south of Ilkley and approximately 1 mile downstream from the source of Backstone Beck. The Cow and Calf rocks lie to the west of the site at Backstone Beck and the surrounding area is approximately 150 metres above sea level as shown on the map in appendix 4. The gradient of the land ranges from about 4-6 metres across and 1 metre up. Surrounding the area where we will be working is mostly moorland.

The climate at Backstone Beck is likely to be more varied than that in the valley because the valley sides do not shelter it. There should be more precipitation in general. The average annual rainfall in the Wharfe catchment area varies from 1835mm on Fountains Fell to 590mm at Cawood.

                                                                       

There are no prominent instances of land use either side of the stream although most of the land is used for either sheep and goat grazing or simply footpaths used by walkers and hikers. Evidence of human activity can be sent throughout the photo above in the form of constructed footpaths or routes that have been overused by humans causing them to be worn down (shown by brown or ashen lines on the map.)

I would expect the river channel at this point is V-shaped due to the water vertically eroding into the ground. This is known as vertical erosion and takes place in streams that occur on the upper course of a river. In the uplands close to the source, the stream is high above its base level (usually sea level). This gives Backstone Beck a lot of potential energy. The stream is also trying to reach its base level so, so the main processes at work are erosional. The river mainly erodes in a downwards direction (vertical erosion) to try to reach its base level. This helps to create V-shaped valleys in upland areas.

       

The different types of bedload in the stream would most likely be large and angular owing to it being the upper course and not having time to erode the material. Material within the stream is eroded by four processes known as hydraulic power, which is the force of the water on the bed and banks of the river. Corrasion that is the action of sand and other small particles rubbing at the bed and banks of the river wearing them away usually happens at times of high flow. Corrosion is how rock minerals such as calcium carbonate slowly dissolve in river water due to it being slightly acidic and attrition being how the load carried by the river collides and rubs against itself, breaking up into smaller and smaller pieces.

The valley sides are steep and narrow because of the vertically eroding water. Fast flowing water and a high amount of erosive energy are present at this point in the river due to the stream being high up on the moors giving it not only high gravitational potential energy but also high erosive energy which in time will help to erode the bedload. On account of the fast flowing water and steep, narrow valley sides the stream is noisy and turbulent as a result.

River Wharfe – The lower/middle course of the river.

The River Wharfe itself begins at quite a distance from Ilkley. It originates at the peat bogs in Langstrothdale chase near and Syke moor. It ends when it joins the River Ouse near Selby where it itself ends at the Humber Estuary near Hull. From source to mouth, the River Wharfe is approximately 60 miles long.

The site of our experiment lies in the centre of Ilkley close to a bridge so that we are able to study both sides of the river without having to wade through the river. Being close to the bridge also means we can accurately measure ¼ ½ and ¾ of the way across the river by using the posts on the bridge as a guide. The actual place of study at the River Wharfe lies on a meander.

The section of the River Wharfe shown on appendix 2 illustrates the river to encompass a meandering path. It is clear that the area is flat due to the lack of contour lines on the map. The altitude for that area is approximately 100m above sea level.

There are three points of significant height within the catchment area of the River Wharfe. These are:- Great Whernside (704m), Pen-y-ghent (694m), and Buckden Pike (702m). The land here is almost flat although there is a slight slope heading in the direction of the River Wharfe from the main town of Ilkley. This however is only true for the South Bank as the North bank was relatively flat.

As the lower course of the Wharfe is situated in a valley, precipitation is lessened and there are fewer winds.

Either side of the river the photo above shows residential housing of a terraced and semi-detached nature. To be more precise the South Bank consists of mainly parkland and for housing whereas on the North Bank most of land has been used for walking areas, parks as well as for recreational activities.

As the river gets further away from its source it should get progressively flatter towards the lower course. The flatter the ground becomes the less friction there is between the water and riverbed, which means in theory that the velocity of the river should be higher. Because the river no longer runs down a steep slope, erosion has to take place laterally rather than vertically causing a U-shaped glaciated valley to form.

The river in its lower course lacks hydraulic power even though the river holds a large body of water.

 The size and shape of the bedload should be smaller and rounder than that at Backstone Beck because, one the majority of bedload at the lower course tends to be either sandstone or limestone. Limestone’s alkaline composition tends to expose it to the slightly acidic waters of the Wharfe making erosion more effective.

The process of attrition evidently takes place within the river where by the river’s load rubs and collides against each other and breaks up into smaller and smaller pieces, which explain the large amount of estuary mud on the riverbed.

The valley sides are wide and flat much like the river channel. This is due to the process of lateral erosion and deposits of sand and mud on the riverbed. Because this section of the Wharfe lies on flat land, the velocity of the river is at a minimum despite the large amount of water it carries. This is not the case however when the river floods.

Section 2 - Method

There is one main reason why I have chosen to study this investigation; being so, I can compare the River Wharfe and Backstone Beck to see how their features differ to one another. Using the following methods, I am able to make these comparisons.

  1. Channel, width, and depth of the River Wharfe and Backstone Beck.
  2. The rock type lithology at the River Wharfe and Backstone Beck.
  3. The size and shape of the rocks in the bed of the River Wharfe and Backstone Beck.
  4. The velocity of the river for the River Wharfe and Backstone Beck.
  5. Measurement of the valley slope profile at the River Wharfe and Backstone Beck
  6. The pH of the water within the River Wharfe and Backstone Beck.
  7. A comparison of the footpath erosion at the sites of the River Wharfe and Backstone Beck.
  8. Environmental quality/litter survey of the River Wharfe and Backstone Beck.
  9. Evidence of tourist honeypot site at the River Wharfe and Backstone Beck. (This method ties in with the Bipolar analysis study)

Grounds for deciding these methods.

  • I feel they will provide me with good contrasting results of the two sites as they are not based on opinion but on fact.
  • The apparatus we required could be acquired easily.
  • The methods are relatively safe to carry out and deny any chance of risk to the group
  • The methods are fairly self-explanatory and can be followed without any help or guidance.
  •  The group as a whole was able to split up doing the methods saving time and getting more done, as no single method required more than five people.
  • Most of the methods were more or less fun in one way or another ensuring that no one was bored. This is beneficial to the investigation in obvious ways.

Method 1 - Channel, width and depth of the River Wharfe and Backstone Beck.

River Wharfe

Apparatus

  • A length of rope
  • Two metre rulers

Method

A length of rope was sent from one end of the river to the other. One end was tied to a tree (South Bank) and the other to a bench (North Bank.) The reason for this was ensure that the rope was kept taught making the results more reliable. The measurement for the width of the River Wharfe was done by beginning at the start of the south bank where the water touched the ground and ending at the same place at the north bank. This span was measured with a metre stick with centimetre and millimetre markings on it. The depth was measured at one metre intervals across the river channel with two, metre sticks as it was deeper than one metre in some areas. For this investigation however, the depth was measured at one metre in from the side instead of from where the water meets the ground. Where the depth was below one metre we measured it in centimetres. This was also the case on the opposite bank. The metre ruler was held side on to the river flow so that the water was disturbed as little as possible warranting fair results.  

Diagram

Logic

Metres and centimetres are an obvious choice for this type of experiment as they   are both metric units and enable me to create a clear cross-section of the river channel. If we had instead decided to use inches and feet, because it would have been confusing for the students as we are not all familiar with the measurements but more importantly the metre sticks we were specified did not encompass the units of inches and feet therefore creating extra costs. Centimetres and metres can also be scaled down into millimetres which provide an even more accurate solution.

Adversities

There were a few problems we faced while carrying out the investigation of measuring the width and depth.

Due to the large rounded bedload on the riverbed, it was sometimes quite difficult to get the metre stick touching the bed to provide an accurate reading.

      The water level proved quite changeable when the depth was being measured which made it difficult to get an exact reading. The ruler although facing thin side first into the flow did create some obstruction to the water as well which created added difficulty.

The river as well as fluctuating also flowed quite speedily that made it awkward trying to hold the metre sticks still while getting a reading.

Method 1 – Channel, width and depth of the River Wharfe and Backstone Beck.

Backstone Beck

Apparatus

  • A length of string
  • Two tent pegs
  • A metre rule

Method

To begin with we set up a length of string across the width of the stream supported by two tent pegs one on either side. The string was kept taught to ensure accurate results. This made it easier to measure the width and depth and gave an indication of direction. After setting this up we measured the width of the stream with a metre rule and along the piece of string we marked a line every ten centimetres. At each mark we then measured the depth with the metre rule and continued until all the measurements were done. We started measuring the depth ten centimetres in from each side of the stream. To create less resistance hence providing more accurate results we held the ruler side on so the thin face was facing the water flow.

Diagram 2

Same principal as Diagram 1 but on a smaller scale with no North or South Bank.

Logic

Due to the dissimilar size relationship between the River Wharfe and Backstone Beck concerning width and depth, using smaller equipment seemed appropriate for the task. By scaling down everything the tasks were easier to complete and more straightforward.  

Centimetres and millimetres were a good choice of unit for this particular experiment as the depth was never below a metre. This also meant that when drawing up the channel cross–section for the River Wharfe and Backstone Beck we did not have to change any of the units as the ones we had already used (metres, centimetres, millimetres) all corresponded with each other.

Adversities

When measuring out the depth we found it difficult occasionally to push the metre stick to the bed of the stream due to the large angular bedload.

The stream was fast flowing which caused some water to splash up on the ruler despite our pains taken not to. This made it challenging to obtain a correct reading for the depth.

Method 2 - The rock type lithology at the River Wharfe and Backstone Beck

River Wharfe

Apparatus

  • Dilute Hydrochloric Acid (HCl)

Method

As this trial was probably the simplest only two people took part in it which required them to collect and analyse 18 pebbles each making a total of thirty-six. The stones were picked from all over the beach by random sample. The partakers were instructed to look up away from the beach at all times to ensure that the articles were random. Once the stones were collected, they were tested to determine which type of stone they were. If the volunteer could not tell the stone either by look or texture than Dilute Hydrochloric Acid was used to see if the stone was an alkaline e.g. one of the forms of limestone. If it was an alkaline then a tell tale sign would be a fizzling noise and a loss of material where the Dilute Hydrochloric Acid made contact with the rock.

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Diagram 1a

For this experiment no diagram was necessary as we were just finding out what type of stone the rocks were.

Logic

This method was considerably more efficient and simple than any of the others due to its low equipment cost and required workforce. It also provides a lot of quality information that can be used to further our knowledge.

        By picking out stones from all over the beach it ensured that we would obtain varying and fair results.

Adversities

Occasionally it was difficult to measure the bedload we had collected but only in the ...

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