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Interpretation of why average velocity changes with distance downstream

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Introduction

Interpretation of why average velocity changes with distance downstream Hypothesis - I predict that average velocity will increase with distance downstream In order to prove my hypothesis I will use the above graphs and my Spearmans rank result for average velocity, which was +0.63. As velocity is the speed of the water passing a point in one second I will need to firstly look at the way in which the water can speed up. The main factors that will affect this are the cross sectional and the wetted perimeter. As we go further down stream both the width and depth increase, and therefore the cross sectional area will also increase, (as the cross sectional area is calculated by multiplying the width by the depth) and if the cross sectional area increases the wetted perimeter will also increase. As there is a larger wetted perimeter there will be a larger pocket of fast moving in the centre of the river that is not experiencing friction from the bed and banks of the river. Therefore as the rivers wetted perimeter increases with distance downstream the average velocity should also increase with distance downstream. Another factor would be the angle of the riverbed. If I was to ask you would a ball roll faster down a steep slope or down a gentle slope you would you say a steep slope, and yes you would be right. ...read more.

Middle

Hydraulic action is the sheer force of the water beating against the bed and banks. These effects will all increase with an increase in discharge, as the water will have more energy.Also the landuse will effect the width and depth as the river will need to widen and deepen to hold the water. The landuse for the river Roe is described in the velocity section of my interpretation. There were a few anomalies one at stop 6 for the depth, this was due to the artificial widening of the river to create a crossing point or ford and another at stop 1 where the width was larger than expected because of braiding and an island. This would be less evident after a flood. The above facts and my spearman's rank result of +0.79, I can therefore see that there is a strong positive relationship between the depth and distance downstream and because the depth increases I also believe that the width will increase with distance downstream. Interpretation to show why the cross sectional area will increase with distance downstream Hypothesis- The cross sectional area will increase with distance down stream. The cross sectional area calculated by multiplying the average width by the average depth. We can see from the width graph that the width increases with distance downstream and also the depth increases with distance down stream. ...read more.

Conclusion

There are two main reasons why the rocks/load will become more rounded, one the velocity and two, erosion in the method of attrition. We know that attrition is when stones/rocks collide and break peaces of each other. So if this is the case it means that the longer (the length of time) they have to collide with each other the greater the chance of all the rough pieces being broken off. This means the further the stones /load travels downstream the longer they will have to collide and therefore the load should get smoother. As we already know the velocity increases with distance which also means the river has more power and is able to carry the load further giving them more time to collide. Also if there is more power the collisions will be harder and will remove more rough edges in a shorter space of time. The results above although expected and correct they will not give an interlay accurate reading. As they are selected from only one area at each stop, there are only 20 samples which is very small and also there will be differences between each persons view of each stone. One could think its angular while another person could think its very angular. With the above graphs and explanation I can clearly see that the load should become smoother with distance downstream. ...read more.

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