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How Rivers Change as They Flow Downstream Essay Sample

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  • Pages: 10
  • Word count: 2,599
  • Rewriting Possibility: 99% (excellent)
  • Category: river

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Introduction of TOPIC

The main point of this enquiry was to find out how landscapes and processes change in a river valley. To see how rivers change as they flow downstream.

To collect the required data for this enquiry we went to the River Bollin, once at Mottram St. Andrews and again at Sutton.

The River Bollin has its source in Macclesfield Forest. The River then flows in a northwesterly direction through Macclesfield, Prestbury, Wilmslow, and Hale and near Outhrington. The River Bollin continues into its lower course, where it meets the Manchester Ship Canal and the River Mersey. The two sections we studied are marked on the map above.

Site 1 – Mottram St. Andrews.

Site 2 – Sutton.

The equipment we needed to carry out our field enquiry was –

1) 2 ranging poles.

2) 20m tape measure.

3) Metre rulers.

4) Several oranges.

5) 30 cm rulers.

6) Several stopwatches.

At each site we measured the following –

1) Depth and width of the river channel.

2) Field sketches; birds eye view, upstream and downstream.

3) Bed load.

4) Speed of flow.

The methods we used for each are as follows.

1) The depth and width of the river. – Place a ranging pole at either side of the river. Pull a tape measure taut between them and read off the width of the river. This should be repeated for the river and the river channel. Hold the tape measure secure. Every 0.5 metres use a metre ruler to measure the depth of the water. Record all results. This information can be used to form an accurate cross section of the river.

2) Field Sketches. – For the birds eye view, imagine you are in a helicopter, hovering above the section of river. Draw it, as you would imagine it to look. For the upstream view, turn to face the source of the river (the opposite direction to the flow of water). Draw what you see. For the downstream view. Turn to face the mouth of the river (the same direction as the river). Draw what you see.

3) Bed load. – Get into the river and pick a selection of stones from the riverbed. Hold the stone in one hand. Use a 30 cm ruler to measure the 3 sides shown in the diagram – length, width and height. TIP – Don’t mover the stone; move the ruler!!

4) Speed of Flow. – Measure a 20m length along the bank of the river. Float the orange along this stretch and time it using a stopwatch. Repeat this 2 or 3 times. Work out the speed using the average time and this equation –

Speed = Distance travelled/Time taken.

Our Results from the River Bollin.

Site 1 – Mottram St. Andrews.

Furthest downstream.

* Depth and width of the river and the river channel.

Channel – 12.2 metres wide.

River – 8.7 metres wide.

Height of river cliff – 0.91 metres.

LEFT

0

1

2

3

4

5

6

7

8

9

RIGHT

Depth in cm.

2

6

11

15

21

28

49

66

37

8

Depth in cm.

These figures allowed me to form the cross section below.

* Field sketches.

These are my field sketches –

* Bed Load.

We measured 10 stones from the riverbed. These are the results.

Stone.

1

2

3

4

5

6

7

8

9

10

Average.

Length.

5.9

2

3.8

4.3

3.5

3.5

4.4

3.5

2.5

3.5

3.7

Width.

3.4

1

2

4.1

2.4

2.6

3.1

3.2

1.8

3.2

2.7

Height.

2.8

0.5

2.7

0.7

1.9

3.4

0.5

0.3

1.5

1.1

1.5

Here is a stone,

drawn using the average measurements from the 10 stones. * Speed

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of Flow.

Here are our results.

Group 1.

Group 2.

Average.

Orange 1.

18.83 secs

18.87 secs

18.85 secs

Orange 2.

22.32 secs

21.19 secs

21.76 secs

TOTAL AVERAGE = 20.31 secs.

Speed = distance/time

= 20 metres/20.31 secs

= 0.98 metres per second.

Our Results from the River Bollin.

Site 2 – Sutton.

Nearest the Source.

* Depth and width of river and river channel.

Channel – 5.4 metres wide.

River – 4.1 metres wide.

Height of River Cliff – 0.6 metres.

LEFT.

0.5

1

1.5

2

2.5

3

3.5

4

RIGHT.

Depth in cm.

5

10

10

18

13

13

1

4

Depth in cm.

These figures allowed me to form the cross section below –

* Field Sketches.

These are my field sketches –

* Bed Load.

We measured 10 stones from the riverbed. These are the results.

Stone.

1

2

3

4

5

6

7

8

9

10

Average.

Length.

19

8

17

6.5

16

10.5

10

6.6

13.5

9

11.6

Width.

17

6.5

7

6.1

7

6.5

7

6

9

5

7.7

Height.

3

1

6

3

8

6

3

2

4

3

3.9

Here is a stone, drawn using the average measurements from the 10 stones.

* Speed of Flow.

Here are our results.

Group 1.

Group 2.

Group 3.

Average.

Orange 1.

29.22 secs

33 secs

35.14 secs

32.45 secs

Orange 2.

40.15 secs

38.7 secs

33.15 secs

37.33 secs

TOTAL AVERAGE = 34.89 secs

Speed = Distance/Time

= 20 metres/34.89 secs

= 0.57 metres per second.

Analysis of Results.

“How do landscapes and processes change in a river valley?”

Do river valleys become wider further downstream?

Yes, they do. This is proven by our measurements of the river channels. Mottram St. Andrews is the site furthest downstream and the width of the channel there is 6.8 metres wider then that in Sutton.

Does a river get bigger downstream?

Yes they do. This is proven by overlaying the two cross sections of the river. As shown in the diagram below. They get bigger because as they go further downstream, small tributaries join with the river and the volume of water increases.

Does the size of material in the riverbed change downstream?

Yes it does. This is proven by the average volumes of the stones found at each site –

Site 1 – 14.9 cubic cm.

Site 2 – 348.3 cubic cm.

That is a difference of 333.4 cubic cm.

As Site 1 is the furthest downstream, this shows that as you go downstream the size of material in the decreases. This could be because the water is flowing faster, which causes the stones to be eroded and to hit against each other, and chip bits off each other.

Where does the river erode and deposit material?

The most hydraulic erosion occurs on the outside edge of a meander. This is because the water flows fastest on the outside of a bend, and the faster the water, the faster the erosion. Deposition occurs on the inside bend of a meander because the water is flowing slowly and it drops the load it has carried from upstream. The field sketches of both of the sites can prove this.

Does a river flow fastest upstream?

No. A river flows fastest downstream, where the volume of water is larger. This can be shown by the speed of flow tests we did. The orange at Site 1 (downstream) travelled at 0.98 metres per second, whereas the orange at Site 2 (upstream) travelled at 0.57 metres per second. That is a difference of 0.41 metres per second.

Is the deepest part of the river in the middle?

Not necessarily. In the cross section of Site 1, the deepest part of the river is clearly 7 metres across. This is more then half way across the river. However, at Site 2, the deepest part of the river is 2 metres across, which is nearly half way across. This is because, as it is just a small river at this stage, the meanders are not very pronounced so the water flows straighter. When you go further downstream, the volume of the river has increased, more erosion has occurred, and very pronounced meanders have been formed. On a meander, the water always flows fastest on the outside curve, as proven by the results from Site 1.

Conclusion.

From my study of the different sections of the River Bollin, I found that river landscapes and processes do change as the river moves downstream. The main changes were the width and depth of the river, the speed of flow and the size of the bed load.

This investigation gave me a greater, more in-depth knowledge and understanding of river formations and processes.

I also learned how important it is to listen to instructions. Also to take accurate measurements and to do an activity more than once to get an average.

We had some difficulty collecting the depth data from Site 1. The river had risen by 30 centimetres because of recent rainfall, so it was too dangerous for Miss Longman to get into the river and collect the data.

The investigation would have been made clearer if we had gone to the sites in the opposite order. Sutton, near the source first and then Mottram St. Andrews, further downstream second. This would have lessened any chances of confusion.

It would improve my knowledge further, to do some further study of sites further down the river, nearer to the mouth, so we could do some further comparisons.

Overall, the investigation went well and we acquired all of the data we needed, even though my feet did get wet!!

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