My aim is to collect data by taking various readings and measurements from the River Conwy to give valid proof of different river processes such as attrition, abrasion and deposition.

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Introduction

Aims & Objectives

The River Conwy is a rural river in North Wales. Its source is situated in Snowdonia National park and it flows northerly into an estuary where it meets the Irish Sea.

My aim is to collect data by taking various readings and measurements from the River Conwy to give valid proof of different river processes such as attrition, abrasion and deposition.

I chose to investigate four factors from source to mouth. My year group and I decided to make five stops so we can note any gradual changes rather than just recording data at two stops. The factors I am studying are:

  1. Depth
  1. Width
  1. Speed of flow
  1. Size of sediment

We made five different stops along the river which are indicated on the map below.

Hypothesis

I predict that as I travel nearer to the mouth; the width, depth and speed of flow will increase while the sediment size will decrease.

I think this because as a river flows towards its mouth many tributaries join it as they drain the basin and this increasing volume of water is one cause of the river becoming wider and deeper. Also, these tributaries add to the rivers load causing more abrasion to occur.

The speed of flow should be slow in the upper course of a river because there are more large boulders and rocks causing obstructions and increasing the surface area in contact with the river therefore producing friction. Whereas downstream, the volume of water increases and there are fewer boulders to slow the flow of water, decreasing the amount of water in contact with the bed and banks.

The size of sediment should decrease further away from the source because most of the large rocks are left at the source because the river does not have enough energy to carry them at that point. The rocks that are carried downstream get broken up due to attrition as the speed of water increases and they abrade the bed and banks, another cause making the river wider and deeper.

Data Collection

Method

We collected data at five stops along the river Conwy in order to see the gradual change of different factors and changes in the shape of the valley. We decided to divide into smaller groups of four and five so that we could each take readings and then take averages for analysis. It also made sure that the tests were fair. The methods we used varied for the measurements of different aspects and are explained in more detail below.

Depth

To measure the depth of the river we used a 2 metre long pole and took three readings, one on the left, one on the right and one measurement in the centre because the river bed is not flat. In order to see which bank is which you have to make sure you are facing downstream. This is shown in fig.1.

The poles had marks at each 1/2 metre making it easier to round the depth off. In fig.2. you can see this process.

Fig.3. Measuring the depth of the centre and left of the river

Due to the increasing depth of the river we were unable to use the method shown in fig.2. at all five of the stops so at stop 4 and 5 we used a plumb line. To make a plumb line we used a piece of rope and tied it securely to a brick or large rock which acts as a weight. We then put brightly coloured markings at 50cm intervals which helped us to be more accurate. One person stood on the bridge and threw the brick into the river so that the plumb line sank to the bottom. Another person would then stand on the bank and calculate the depth by seeing how many markings were covered. This method has been illustrated in fig.4.

Below are the results of our depth measurements displayed in a table.

Width

To measure the width we used a tape measure as it gave more accuracy than using a pole and stretching it across the river. One person took the end of the tape measure and walked across to the other side of the river. The person with the other end stayed at the other side and took the reading. This is shown in fig.5.

As this was not possible at every stop due to the increasing depth we were forced to use a different technique. So instead we measured the length of the bridge which was as accurate. This is demonstrated in fig.6.

In the table below are the results for the five widths.

Speed of Flow

In order to measure the speed of flow we used to methods, one of these was by using a flow-meter shown in fig.6.        

This instrument has a propeller at one end which is placed just below the surface of the water because that is where the speed of flow is fastest. This is due to the fact that there is no friction with the bed, banks or wind which cause the flow to be slower. The propeller is connected to a cylinder which contains a wire that leads to a small box with a switch. A person stood on the bank with a stopwatch a timed a minute. At the beginning the person holding the propeller pressed the switch and stopped it after a minute. The number of rotations was then shown on a dial in the box and we calculated the speed from that. Fig.7.shows me using the flow meter at stop 1.

We did this at each stop possible but at stop 4 we were only able to obtain a result next the left bank on the outside of a meander.  

The other method we used was ‘the orange’. In order to do this you needed two people standing 10 metres apart, this was measured with a tape measure, in the centre of the river both holding a pole. The person standing upstream held an orange and a stopwatch whilst downstream another person stood slightly behind the pole with a net in their hand to catch the orange. The person holding the orange would drop it just before their pole and begin the stopwatch when the orange passed it. Then when it passed the second pole the person would call out and the stopwatch would be stopped. Fig.8. shows the orange method.

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We decided to use an orange because it is biodegradable and would not pollute the river if the person with the net failed to catch it. Also, it is easy to see and it does not sink but floats just below the surface where the water receives no resistance from the wind or friction so the water is at its fastest.

 

Again, due to increasing depth we had to conduct a different way to measure the speed ...

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