An Investigation Into Stream Channel Characteristicsnel

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  • Topic: Stream, Boulder, River
  • Pages : 47 (7752 words )
  • Download(s) : 67
  • Published : April 28, 2013
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Contents

Introduction and Aims
3 - Hypothesis 1
4 - Hypothesis 2
5 - Location map

Method
6 - Field sketch
7 - River mapping, Cross section
8 - Velocity
9 - Method Limitations

Data Presentation
10 - River mapping table
14 - River mapping
15 - Meander cross section results data set 1
16 - Straight cross section results data set 1
17 - Velocity/depth graphs for data set 1
18 - Meander cross section results data set 2
19 - Straight cross section results data set 2
20 - Velocity/depth graphs for data set 2
21 - Meander cross section sketch data set 1
22 - Straight cross section sketch data set 1
23 - Meander cross section sketch data set 2
24 - Straight cross section sketch data set 2
25 - Spearman’s rank for meander data set 1
26 - Spearman’s rank for straight data set 1
27 - Spearman’s rank for meander data set 2
28 - Spearman’s rank for straight data set 2

Analysis and Conclusion
29 - Meander 1 description and analysis
30 - Straight 1 and Meander 2 description and analysis
31 - Straight 2 description and analysis and hypothesis analysis 33 - Limitations of the study

35 - Bibliography and acknowledgements

Introduction and Aims

The aim of this investigation is to compare the characteristics of straight and meandering sections of a stream using data collected in the Harthope Valley, Northumberland.

My hypotheses for this investigation are:

Hypothesis 1

• The cross profiles of straight stream channels show greater symmetry than the cross profiles taken across the meander.

Rationale

In a straight section of a stream the thalweg is centrally located; this causes erosion of the river bed in the middle but deposition at the banks where the current is slowest. This is the symmetrical cross section across a straight stream or river:

Fig. 1.1

On the other hand, in a meander the thalweg is located at the outer bend while the slowest current, and therefore the deposition, is located on the inside of the meander. This means an asymmetrical cross section is formed. The deposition forms a slip off slope whilst the thalweg causes erosion of the river sides leading to the formation of a river cliff. This is a typical cross section of a river across a meander:

Fig. 1.2

The thalweg travels in a straight line and so when the river comes to a meander then, due to inertia, it continues into the bank. This causes heavy erosion to make the meander even more sinuous. The river bank, where the thalweg hits, deflects the thalweg down towards the next meander and in doing this it has to go through a straight section of the river. As the thalweg is being deflected from one meander to the next, it travels through this straight section in the centre of the channel. (Fig. 1.3)

Fig. 1.3

Hypothesis 2

The pattern of stream velocity shows a direct relationship with the pattern of channel depth.

Rationale

The deeper the channel is, the faster the water flows. This is because in shallower water there is a greater proportion of water in contact with the wetted perimeter. This means that more friction occurs and so the velocity of the water is decreased. In streams and rivers with a deeper bed and therefore a greater volume, the water in contact with the wetted perimeter has less effect in slowing down the river’s flow. In a meander (Fig 1.2) this relationship means that the water is slowest at the slip off slope. This is because the slow water means deposition, leading to a shallower bed, which in turn makes the water even slower. At the outer bend of the meander, the water is deeper and so the water moves faster. In the straight section of a river (Fig 1.1) the water can move faster in the centre as this is where the bed is deepest, it moves slower at either side due to...
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