A Diagram To show Lamina Flow and Eddy Currents which occur on the straight section of the River Rhymney
Cross-Section of straight section of River Rhymney
STRAIGHT_SECTION OF MIDDLE COURSE OF RIVER RHYMNEY AT B&Q IN YSTRAD MYNACH
This section of the River Rhymney is located on the floodplain of the valley on an Industrial Estate on the outskirts of Ystrad Mynach. At this section of the river the river is beginning to erode laterally as well as vertically. The sides of the river have been reinforced in order to prevent flooding into the nearby factories and superstores. At this stage of the river the river is still carrying large particles opposing the movement of the water.
Prediction
I predict that the velocity at the centre of the river will be much faster than at the left and right banks . Therefore the time taken for the ping – pong ball to reach the end of the stretch of river will be less in the centre than at the two sides. I also predict that the depth at the centre of the river will be deeper than the depth at the two banks. The velocity of the river will be slowest at the wetted perimeter where the river comes into contact with it’s banks and bed. I also predict that the velocity of the river will be decreased due to man’s interruption of reinforcing the banks.
Hypothesis
This is because at the centre of the river the velocity is faster as there is little friction so therefore the water can travel faster. At the two sides the pebbles and rocks on the banks of the river as well as the pebbles and rocks on the bed of the river cause more friction so therefore the velocity of the river is slower at the two sides as shown in the diagram. At B&Q man has reinforced the bank of the river in order to decrease the eroding power of the river and prevent the bank of the river from being worn away. This will further decrease the velocity of the river at the banks as it is an extra obstacle opposing the movement of the water and causing Eddy currents to occur.
As water flows downhill it releases energy. Most of this energy is used to overcome friction at the sides of the river and on the river bed therefore the depth at the centre of the river channel at the straight section of the river Rhymney will be deeper than the depth at the two banks and the velocity will be greater because at the centre of the river the only friction is from the bed of the river and on the two sides of the river the friction is due to the banks and manmade reinforcements as well as the bed causing more friction at the banks of the river and therefore a lower velocity and shallower depth as the river does not have sufficient energy to cause the particles at the bed of the river to erode downwards to such a great extent as at the centre of the river. The depth at the centre is greater because the energy of the river is greater therefore causing the particles carried by the river to erode to a greater extent.
Apparatus Required
- Stopwatch (to time the ping-pong balls)
- Waders (so that we may enter the river to carry out various tasks)
- 3 ping-pong balls
- 2m stick (to measure the depths of different parts of the river)
- Tape measure (to measure out a stretch of the river being studied)
- Table of results (to record readings)
- Camera (to take pictures of further fieldwork)
Method
- Collect apparatus in order to carry out the fieldwork.
- Make sure each piece of equipment has no faults.
- Measure out stretch of river where you wish to carry out the work using the tape measure.
- Measure the depths of the Left- bank, Mid-stream, and Right-bank at the start, middle, and finish of the stretch of river.
- Record measurement in table of results.
- 3 people enter the river at the beginning of the stretch and 3 people enter at the end of the stretch of river.
- Simultaneously release the 3 ping-pong balls and start the stopwatches.
- When the balls reach the 3 people at the end of the stretch, record the time taken from the stopwatch.
- Take repeat readings in order to construct accurate graphs.
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Use the equation Speed (m/s) = Distance (metres)
Time (s)
Using results construct graphs to clearly show evidence obtained.
Analysis
The graphs and table of results have proved that my prediction was correct as I discovered that the velocity at the centre of the river was much faster and the time taken for the ping pong ball to reach the end of the stretch of river much less at the centre than at the two sides.
In order to plot my bar chart of part of river which is located on the X-axis against the velocity of the river channel which is located on the Y-axis I had to discover the speed of the river using the equation Speed (m/s) = Distance (m) .
Time (s)
These results have been recorded in the table of results. The length of river over which we recorded our readings was 40 metres.
I converted my results into cm/s for ease of plotting on the graph as I could plot whole numbers. The line chart shows the time taken for the ping-pong ball to reach the end of the stretch of river at certain sections of the river. The time taken for the ping-pong ball to reach the end of the stretch of river at the centre was less at 60.6 s as there were less particles opposing the movement of water. The time taken for the ping-pong ball to reach the end of the stretch of the river at the two sides was much greater at 99.2cm/s at the near side and 112.2 seconds at the far side. This was due to the effect of the manmade reinforcement opposing the movement of the water.
The bar chart showing the results shows clearly that the velocity at the straight section of the river Rhymney is much faster in the centre of the river channel where the velocity is 66 cm/second than at the near side bank where the velocity is 40.3 cm/s and the far side bank where the velocity is 35.7 cm/s. Also the depth of the river at the centre is deeper at 70 cm, than the near side depth, which is 46 cm and the far side measurement where the depth is 29 cm. These results are not shown on the bar chart but are clearly indicated in the table of results and Cross-Section. These results also backup my hypothesis. The reason why the river velocity is faster and the depth deeper at the centre is because at the centre of the river there is not so much friction (from the banks). The only friction is from the river bed, therefore at the centre the river uses the energy to cause the particles in the river bed to erode downwards at a greater rate than the particles on the river bed at the two sides. Therefore the depth at the centre of the river is greater than the depth at the two sides. The velocity at the centre of the river is greater due to the fact that there is less friction at the centre of the river channel. At the near side and far side of the river the river is working against the friction from the particles due to the manmade reinforcements at the banks and bed of the river, whereas at the centre of the river, the river only has to work against the friction from the bed of the river causing it to have a greater velocity.
Secondary Results -A Meander at Trethomas at the Mid-section of the River Rhymney
I decided to extend my investigative work by going to the meander of the River Rhymney at Trethomas to obtain extra information about the course of the river Rhymney and to show how the flow of water changes as the river matures.
At this stage of the river, the river is eroding laterally as well as vertically.
Prediction
I predict that the velocity on the outer meander bend will be greater than the velocity at the centre of the river channel. The slowest velocity will be on the inner meander bend where the deposition occurs. Therefore the time taken for the ping –pong ball to reach the end of the stretch of the river will be less on the outer bend of the meander than in the centre. At the outer bend of the meander the time taken for the ping pong ball to reach the end of the stretch of the river will be greatest.
Hypothesis
When a river reaches a meander most water is directed towards the outside of the bend. This will reduce friction and increase the velocity of the river at this point on the outside of the Meander bend. The river will therefore have more energy to transport material in suspension. This material will erode the outside bank by corrasion. The Lamina flow pattern is most likely to occur on the outside part of the Meander bend due to the Hydraulic Action of the river being able to overcome the friction at the banks. The banks of the river will still oppose the movement of the water, however the sheer force of the majority of the water being directed towards the outside bend of the Meander will overcome the frictional forces at the banks of the river causing the flow to be fastest at the bank. The bank will be undercut and collapse and retreat to leave a small river cliff. Meanwhile there will be a decrease in velocity on the inside bend of the Meander due to the deposited particles opposing the desired movement of the water causing a Turbulent flow pattern resulting in Eddy Currents causing water to flow in all directions due to the Frictional Forces.
Analysis
I recorded the results for the Meander over a 20 metre stretch of river. The line chart and pie chart and Table of results prove that my Hypothesis was correct. The pie chart shows that the velocity of the river Rhymney at the Meander in Trethomas was greatest on the outer bend (far-side measurement) of the Meander at 52.9 cm/s. The outer part of the Meander bend also had the greatest depth at 105cm. The reason for this is because the majority of the water flow is directed towards the outer bend of the Meander causing the sheer force of the river to overcome the frictional forces at the banks of the river. Although Eddy currents are still occurring to a small extent on the outer bend of the Meander the sheer force of the river has sufficient energy to overcome the frictional forces causing the Eddy currents. The deposition on the inside of the meander bend caused an increase in Friction resulting a great decrease in velocity as the river’s energy could not overcome the Friction. The friction from the deposited material opposes the movement of the water resulting in a Turbulent flow pattern, which causes Eddy currents to occur where the water flows in all directions resulting in a decrease in the velocity of the river on the inner bend of the Meander as the graph shows. The velocity of the water flow at the inner bend of the meander (Near side measurement in table of results) was 22.3 cm/s. The pie chart gives a clear indication that the outer part of the meander bend has the greatest velocity and the inner part of the meander bend has the smallest velocity. The outer bend of the meander is deepest due to the energy from the river causing the particles carried by the river and also the sheer force of the river (Hydraulic Action) to erode greatest at the bank of the outer bend of the Meander as the river is beginning to erode laterally as it is in its Middle course. The particles are then deposited on the inside bend of the next Meander as the river flows.
Draethen Bridge Straight section of Lower-course of River Rhymney
I will obtain these results from the members of my class who visit Draethen Bridge as a secondary source of information. This part of the river Rhymney is in it’s lower course and particles carried by this part of the river will be smaller than particles in Middle course of river at B&Q. The banks of the river are very smooth and no manmade structures are present to oppose the movement of the water as there are at B&Q. This part of the river is also wider than middle course of B&Q due to lateral erosion in the river’s lower course.
Prediction.
I predict that the velocity of the river will be greatest at the centre. The banks of the river will cause a decrease in the velocity of the river but the velocity of the river will still be greatest in the centre. The velocity of this part of the river Rhymney will be faster than readings taken in the straight section at the Middle course of the River Rhymney at B&Q
Hypothesis
The velocity at this part of the river will still be greatest in the centre as there is least friction causing Eddy currents. The only friction at the centre is from the particles on the bed of the river causing Eddy currents whereas on the left and right banks of the river the friction is due to the particles at the banks as well as the bed of the river causing Eddy currents. The banks will cause an even greater decrease in the velocity of the river because it is an extra obstacle for the river’s energy to have to overcome causing an increase in Friction as Eddy currents are more likely to occur as there is an extra obstacle opposing the movement of the water causing water to flow in all directions and therefore a great decrease in the velocity of the river as the river’s energy is expended trying to overcome the friction. The velocity of the Lower course of the river Rhymney taken at Draethen Bridge will be a lot faster than the velocity of the river during it’s Middle course at B&Q because the particles carried by the river have become smaller due to erosion as the river flows. At B&Q the river channel contained more boulders, creating more friction due to a larger wetted perimeter. The readings taken at Draethen Bridge in the lower course of the River Rhymney should show that the velocity of the river is faster during it’s Lower course as there is a very small wetted perimeter in comparison to the volume of the river .Due to this and the smooth banks and bedload, the friction is reduced allowing the velocity to increase. This section of the River Rhymney is wider as there is less friction the river’s energy is used to erode laterally.
Analysis
The other members of my class recorded these results over a 30 metre stretch of river. The line chart shows that the time taken for the ping-pong ball to reach the end of the stretch of the river at the centre was 99.2 cm/s, whereas on the near side the time taken to reach the end of the stretch of river was 152.6 s and on the far side the time taken to reach the end of the stretch of river was 160 seconds. The bar chart clearly shows that the velocity at the centre of the river was greatest as was expected due to a mainly Lamina flow pattern. The only particles opposing the movement of the water able to produce Eddy currents were on the bed of the river.
The bar chart shows that the velocity at the centre of the river is 17.3 cm/s. The bar chart shows that the velocity at the left bank of the river is 15.8 cm/s and the velocity at the right bank of the river is 15.9 cm/s. The reason why the velocities were smaller and the time taken for the ping-pong ball to reach the end of the stretch of the river was longer at the two sides was because the friction at this part of the river was due to the particles at the banks as well as the bed of the river.
COMPARISON BETWEEN STRAIGHT SECTION AT MIDDLE COURSE OF RIVER RHYMNEY AND STRAIGHT SECTION AT LOWER COURSE OF RIVER RHYMNEY
The reason why these velocities are so small in comparison to the results obtained at B&Q is because on the day we visited B&Q there had been a period of heavy rainfall causing the volume of the river to increase and therefore the velocity of the river also increased. The other members of my class visited Draethen during a period when the weather had been fairly dry so the volume of the river was much smaller causing the velocity to decrease. This has caused us to obtain anomalous results as we should have discovered that the velocity of the river Rhymney in it’s lower course at Draethon was much faster than the velocity of the river at it’s Middle course in B&Q.
Conclusion
During this investigation I have discovered that on the straight section of the river whether in the Upper course (results taken at Draethon) or the Middle course of the river (results taken at B&Q) the velocity is always greatest at the centre of the river as there are less Frictional forces at the centre of the river able to produce Eddy currents and the flow of water is mainly Lamina. Eddy currents occur when the particles such as rocks and boulders within the river oppose the movement of the water causing the water to flow in all directions. At the centre of the river the only place where Eddy currents can occur is on the bed of the river, whereas on the left and right banks of the river the frictional forces opposing the movement of the water causing Eddy currents are due to the banks as well as the bed of the river.
I discovered that the overall velocity was fastest at B&Q in the Middle-course of the river than at the Lower course of the river at Draethon. This is an anomalous result as I should have discovered that the velocity of the river was fastest in its lower course at Draethen as at Draethen there was a very small wetted perimeter in comparison to the volume of the river. The banks of the river at Draethen were also smoother and bedload smoother causing the friction to decrease and the velocity to increase. At B&Q the river had a larger wetted perimeter, which increased the friction and decreased the velocity. The reason why we obtained this anomalous result was because on the day that we obtained readings from the middle course of the river Rhymney at B&Q in Ystrad there had been a period of heavy rainfall causing the volume of the river to increase and as a result the velocity of the river also increased. When the other members of my class visited Draethen there had been a relatively low amount of rainfall so the velocity of the river was found to be relatively slower.
The outer bend of the Meander was also found to have the greatest velocity as I hypothesised. This is because as a river reaches a Meander the majority of the water is directed towards the outer part of the bend causing the sheer force of the river to overcome the frictional forces from rocks and boulders and the eroding power of the river to greatly increase. Although Eddy currents due to opposing forces from boulders and rocks occur to a small extent the sheer force of the river has the ability to overcome these frictional forces. The inner part of the Meander bend where the deposition occurred had the smallest velocity as the deposition acted as a frictional force opposing the movement of the water forming Eddy currents therefore the water was flowing in all directions.
The effect of the manmade reinforcements at Ystrad in the rivers Middle course was found to greatly decrease the velocity at the banks of the river as it was an extra obstacle in the rivers desired flow pattern opposing the movement of the water forming Eddy currents.
Evaluation
Overall I feel that the investigation was successful. I felt that the procedure I used in order to obtain my results was simple to follow and allowed me to obtain the expected results.
The investigation could have been made more accurate by taking more repeat readings in the sections of the river investigated. We also could have timed the ping-pong balls more efficiently by stopping the stopwatch as soon as the person had caught the ping-pong ball. The person in the river holding the stopwatch in one hand and catching the ball in the other hand so that the stopwatch is stopped at the exact time that the ball is caught could have done this.
We could have avoided our anomaly by visiting the straight section of the middle course of the river at B&Q in Ystrad on the same day that the other members of our class visited the straight section of the river in its lower course. This would have ensured that the amount of rainfall was kept constant and would have allowed me to obtain the result I expected to obtain. The river in the lower course should have a greater velocity than the river in the Middle course.
We could increase our investigative work by visiting other sections of the river Rhymney to obtain readings and also visit a different river such as the River Taff and compare the two rivers.
