We can see clearly from the graphs that the velocity increases with distance downstream but there are a few anomalies, which were stops 2+4 (velocity graph).
The reason behind stop 2 is quite simple, the velocity increase is caused by the joining of a tributary(the ) just upstream of are second stop. This excess water creates a larger cross sectional area and thus a larger pocket of fast moving water. It would also cause increased erosion of the riverbed. Stop 4 has increased velocity due to human interference in that dredging has occurred at the inside of a meander bend.
As my spearmans rank result of +0.63 also shows that there is a strong positive correlation between average velocity and distance downstream I believe that the results satisfy my prediction.
Interpretation to show why discharge changes with distance downstream
Hypothesis-The discharge will increase with distance downstream.
In order to give an explanation of why the discharge increases with distance downstream I will use the above two graphs and previous knowledge.
Discharge is calculated by multiplying the cross sectional area by the velocity. Therefore the main reason or factors that will affect the discharge will be both velocity and cross sectional area. We can see clearly from the velocity graph that there is an increase in velocity that is caused by an increase of water via tributaries and a smoother river bed caused by various methods of erosion. The width and depth of the river increasing cause this along with an increase in cross sectional area, which can also be seen from the above graph, (both of which are increasing because of erosion) cause the discharge to also increase as well . Another reason for increased discharge is the angle of the river bed. If the river bed is steeper the water will travel over it faster due to gravity.
However there was an anomaly at stop 5, the decrease was caused by the artificial widening of the river (which caused a velocity decrease) and this in turn caused a decreased discharge.
With these facts and the spearmans rank result of +0.98 clearly show that there is a strong positive relationship between discharge and distance downstream.
Interpretation to show why both width and depth increase with distance downstream
Hypothesis- Both the width and the depth will increase with distance downstream.
With reference to the above graphs along with previous knowledge I will hopefully establish a valid reason for the increase of both width and depth with distance downstream.
This is basically one reason for the increase of both width(lateral) and depth(vertical), the reason is erosion. There are 4 main types of erosion attrition, corrasion, corrosion and hydraulic action all of which both deepen and widen the river. Attrition is the material or the load, which is in the river colliding with and breaking of parts of the riverbanks and bed. Corrasion is when the fine material in the river rubs along the banks and bed in a sand papering effect and gradually wears away the banks and beds. Corrosion is the acid (the acid in the river roe comes from the peat) in the water dissolving the rocks or stones in the bed and banks. 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. As both these increase the cross sectional will also increase.
Stop 1-As there is a great deal of interception and little overland flow there is not a lot of water entering the river which caused both a smaller depth and width and therefore a small cross sectional area.
Stop2-With the addition of water from the tributary there will be a larger width and depth, mainly due to hydraulic action also the steep relief of the surrounding area increases the discharge and as the width and depth increase the cross sectional area also increases. It was this excess water whch cause this stop to be an anomaly.
Stop3-This stop is on a meander bend which means the depth at the outside of the bend will be larger than expected due to erosion.
Stop4- This stops cross sectional area was simply increasing as the width and depth increased due to the increase in water or discharge.
Stop5- Like stop 4 the cross sectional area is increasing due to the increase in water causing the width and depth to get larger.
Stop6- This Stop is also like stops 4 and 5 as it also increases with the increase in water or discharge.
Stop7- There was a slightly larger value at this stop due to surroundings having a steep relief. This caused excess water to enter the river; therefore the river will widen and deepen to accommodate this water.
Stop8- This was the other anomaly I found. The reason behind this is the extreme rise in discharge, this is caused by no interception and more runoff. Which is caused by the impervious surfaces in the urban area of Dugiven running straight into the river via the drainage system in Dungiven. This causes hydraulic action to both deepen and widen the river and these in turn increase the cross sectional area.
We can clearly see from the above graph that there is a strong relationship between cross sectional area and distance downstream.
Interpretation to show why the load size decreases with distance downstream
Hypothesis- The load size will decrease with distance downstream.
There are two main reasons why the load size decreases with distance downstream, one the velocity of the water and erosion.
As we already know that velocity increases with distance down stream and therefore we know that the river is slower and that it has less power at the source than at the mouth. Due to the river having less power at the top/source it will not be able to move large rocks in the transportation method of traction (which is when the water rolls the large rocks along the river bed).This means the large rocks are deposited and only the smaller stones will be able to be transported by the methods of transportation. Which are saltation (this is the when the small stones bounce along the riverbed), suspension (this is when the material or load is so light that it can be carried by the water) and solution (this is dissolved material or load transported by the river). Therefore the further we travel down the river the larger the velocity and the more power the river will have to more larger stones.
Another reason is erosion, as the load is carried or transported down the river it will be eroded by attrition, corrosion, corrosion and hydraulic action(all of which I have previously explained). Due the load/stones becoming smaller the less force/velocity the river will need to transport them.
There were some anomalies one being at stop 1, where the load was smaller than expected, this is because the stop was on meander bend and from previous knowledge I know that the inside of the bend has a lower velocity than the outside. This will cause the load to be deposited on the inside of the bend, and from my field trip I observed a slip off slope on the inside of the bend, this was formed by the deposited load. Another was at stop two. Due to a tributary joining just above the stop there was an increase in velocity. This increase means that less small stones are deposited (as the river has more energy) causing the average size to be larger than expected. The last anomaly was at stop five this was just like stop 1 as there was a slip off slope formed on the inside of the meander bend. This drop in velocity at the inside of the bend means larger stones were deposited causing the results to be larger than expected. Over all can see that the trend was that the load size decreased with distance downstream.
Interpretation to explain why the load shape changes with distance downstream
Hypothesis- The load’s shape will become more rounded with distance downstream
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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.