Roda Abokor 29106 centre number: 10500 Swanlea School

Name: Roda AbokorCandidate number: 29109Centre number: 10500

Investigation into whether width, depth and velocity increase downstream along the River Roding(A case study on a river in Epping Forest)

Contents Page

Introductionpage 2-8MethodologyData Presentation and AnalysisConclusionEvaluationBibliographyAppendix

Introduction:The aim of the geographical study was to study whether width, depth and velocity increase from source to mouth. The river our study was based on is the Middle Roding Drainage Basin in Epping Forest, in the South East of the UK and it is also a tributary of the river Thames. We chose the middle Roding Drainage Basin because it is easily accessible to our school; it is close to our school therefore we did not have to travel far. It was also safe and practical in terms of accessing sites along the course of the river that we could measure. The number of results we could measure were limited due to time therefore we selected three sites to study. The three sites represent the upper, middle and lower course and the measurements that were taken will be studied so conclusions can be made about the changes to characteristics of a river with distance downstream. I came up with a hypothesis based on my own geographical knowledge and geographical theories that we have studied e.g. The Bradshaw Model.I came up with the following hypothesis:1. The width of the river channel increases downstream in the Middle Roding drainage basin.2. The depth of the river channel increases downstream in the Middle Roding drainage basin.3. The velocity of the river channel increases downstream in the Middle Roding drainage basin.We were confident that our findings would prove these hypotheses to be accurate, however we also decided on the following null hypotheses.1. The width of the river channel does not increase downstream in the Middle Roding drainage basin.2. The depth of the river channel does not increase downstream in the Middle Roding drainage basin.3. The velocity of the river channel does not increase downstream in the Middle Roding drainage basin.I have made reference to the geographical theories of M.J. Bradshaw, a geographer who studied how the river's characteristics vary between the upper course and lower course. The model shows that the discharge, width, depth and velocity increases downstream. Bradshaw claimed that this theory could be applied to all rivers. I am carrying this investigation so I can prove or refute my hypotheses and test the accuracy of the Bradshaw Model.

Figure 1: The Bradshaw ModelThis figure shows the width, depth and velocity increase from the source to mouth according to Bradshaws prediction.

River variablesDefinitionChange from Source to Mouth (Increase/Decrease) explanation

Velocity The speed at which water flows. It is measured in m/s.

Increase from source to mouth

The velocity will change downstream along the river. This is affected by factors such as the gradient, the volume of water, the shape of the river channel and the amount of friction created by the bed, rocks and plants. The river is more efficient as you go downstream along the river due to erosion and there is less friction so water flow rapidly with river losing less energy to friction. Therefore the river is more laminar and less turbulent. Also, the increased volume of water entering river from tributaries will result in increased momentum and velocity.

Width The width of the river channel is the distance from the left bank to the right bank (meter).

Increase from source to mouthThe width of river increase from the source to the mouth due to lateral erosion. Theres an increase in lateral erosion because there is an increase in water velocity, discharge and load resulting in more abrasion due to traction and saltation as well as hydraulic action. Also, menders are found in the middle course which widens the river channel.

Depth The depth of the water is the distance from water surface to river bed in meter.

Increase from source to mouthThe depth of river increase from the source to the mouth due to vertical erosion. The river will have greater erosive power because of the increase in water velocity, discharge and load resulting in more abrasion due to traction and saltation as well as hydraulic action.

Cross sectional Area You can calculate the cross sectional area by multiplying the width of the river by depth of the river.Increase from source to mouthThe combination of lateral erosion and vertical erosion results in increase of the depth and the width of river meaning an increase in cross sectional Area.

Figure 2: Table to show my hypothesisHypotheses and Theory in Detail

Velocity:Velocity is a measure of how fast the water flows over a specified distance (Velocity = distance/time) and generally increases with increasing distance downstream, as more water is added to the rivers via tributaries. This means that less of the water is in contact with the bed of the river and the banks so there is less energy used to overcome friction. Hence rivers flow progressively faster on their journey downstream. Gradient can have an impact on velocity but rivers tend to be very shallow and narrow in their upper steep courses, which increases the friction acting on the water and slows it down despite the steep gradient. Velocity is also highly variable from location to location on a river, and velocity is highly influenced by channel shape or form. Wider shallow channels have larger wetted perimeters (so more friction) and hence flow slower than narrower deeper channels. Velocity profiles also differ between symmetric and asymmetric channels. Velocity becomes more efficient in the lower course because of the following reasons:

Shape of the channel - the lower course of the river is deeper, wider and has higher discharge. There is less water in contact with the wetted perimeter, so friction from the bed and the banks is minimized. The greater the cross-sectional area in comparison to the wetted perimeter, the more freely the stream will be flowing because less of the water is close to the frictional bed. Therefore as the hydraulic radius increases so will velocity; If a river has a high hydraulic radius, it means less water is contact with bed, banks and surface, making it more efficient.

Channel roughness - pebbles, stones and boulders on the beds and banks increase the roughness of the channel. The upper course is rough or uneven with boulders on the river bed as well as rocks that protrude out from the bank. This means the water has to overcome such obstacles and therefore there will be more friction and the velocity of the river is reduced. The wetted perimeter is higher, increasing friction which leads to slower river flow reducing velocity. Width and Depth (Cross Sectional Area) The river becomes more efficient as we move downstream because frictional effect of the bed is limited. The hydraulic radius is higher in the lower course and the channel loses less energy through friction with its channel. The more efficient the river is the more energy the water will have to increase the rate of erosion; there is more lateral erosion downstream therefore the width of the channel increases. In addition water from tributaries contribute to the high discharge in the lower course which carry more loads and these results in abrasion against the river bed due traction and saltation. This increase in vertical erosion leads to an increase in the depth of the river.

The Schumm Model is another useful geographical theory in supporting our hypotheses that width, depth and velocity will increase as we move downstream.

Context and Location of Study:I have used Geographical maps in order to locate my study accurately. This includes a range of applications for example Google maps at various scales and Google street view.The river that we studied for our investigation was the River Roding. The River Roding is located in South East England that rises near Dunmow, flows through Essex and forms Barking Creek as it reaches the River Thames in London. The river is located at the following geographical co-ordinates: 5131.837N 004.54E. We were studying the middle course of the river, accessible from the Field Study Centre at Loughton Beach in Epping Forest. Figure 4: Location of Area of Study within the UKArea studied located in the south east of the UK

The area we studied was in Epping Forest, located in Essex, north east of London

Figure 5: Location of Area of Study within Greater London and EssexThe study was conducted from our base at the Field Study Centre in Epping Forest, near to the town of Loughton

Figure 6: Location of Area of Study within Epping ForestThere is small rural settlement nearby; an area of farmland.

This satellite image shows land use in the area around the site. There is dense vegetation of coniferous and deciduous trees in the forest.

Figure 7: Satellite Image of Area of Study within Epping Forest

This map shows an area of the middle course of the River Roding. The lines on the map are contour lines and these show the relief of the land. The lines are far apart showing that the land is sloping gently and the gradient is not steep. The land is 100m above sea level.

Figure 8: Map of Area of Study showing terrain

Street view shows the woodland vegetation of the area. Human land use can be seen in terms of the footpaths, buildings and recreation facilities.

Figure 9: Street View showing location of area of study

Pilot Study and Risk Assessment:We carried out a detailed risk assessment, identifying all the possible risks, before we went to Epping Forest to do our investigation. We completed the risk assessment to ensure we had solutions and strategies in place to our possible risks. We needed to make sure that all possible safety precautions were taken as working in a river can be dangerous. (My risk assessment can be found in the appendix.)We could have also completed a pilot study if we had stayed in Epping Forest for more than a day. A pilot study is a small scale experiment and it helps to identify the risks and limitations. Our investigation was based at a Field Study Centre and they had already completed a pilot study and provided us with one, therefore it was not necessary to do a separate pilot study.Sampling:It was not possible to measure every points of the river due to limited time and practical reasons. Therefore we decided to use sampling and we had to base our evidence on only measuring three sites along the river. By measuring three sites we could reach some conclusions about the whole river and how it changes downstream.There are many different types of sampling. The type of sampling that we used was called systematic sampling. Systematic sampling is when sites are located at certain points along the river at regular intervals. We used systematic sampling instead of random sampling because it is difficult to obtain a truly representative data from random sampling and using a systematic sampling meant that we could be sure that we were measuring three sites that would show how the river changed from source to mouth. Additionally we decided not to select stratified sampling because although particular areas would be sampled, by choosing the sites our results would be subjective and could be biased.

Methodology

Methodology for Measuring River Width:Hypothesis: The width of the river channel increases downstream in the Middle Roding drainage basin.Equipment:Tape measureData recording sheetsPrimary research methods:We measured each sites of the river using a tape measure. My partner stood on the left bank of the river and held the start of the tape measure on the surface of the water. I pulled the tape measure across the surface of the water toward the right bank of the river. The start and finishing points for the measuring are the points at which the dry bank meets the water. The distance on the tape measure was read and this was recorded on our data sheet. This method was repeated at each of the three sites.One of the members of the group holds the tape measure on the left side of the bank just above the surface of the water

Another person pulls the extendable tape measure along the surface of the water.

One of them measures the width and the other records the result in data recording sheet.

Figure 11: Photograph showing students measuring river width

Explanation of why data was collected: It was important to collect data that showed the width of the river at each sites in order for me to prove my hypothesis that the width of the river increases as we move downstream. Collecting these results of the width in the three sites will enable us to see if the width increases as we move from site A to C. In addition, we can use the result of the width and the depth to calculate the river cross section.Figure 12: Photograph showing students measuring river width

Justification of data collection method: We used the extendable tape measure because it is flexible and it is long enough to reach the other side of the river bank. We measured from the left bank to the right bank to ensure we measured the full width of the river. We wanted to measure the water width so we measure on the surface of the water. We followed this method throughout the 3 sites because this method is a simple way to get accurate data.Limitations and Problems: Human error is a major problem the measurement might not have been read accurately The weather condition was very poor; this might have affected the measurement. The tape measure may not have been held accurately on the right and left side of the bank. Also vegetation and natural environment made it difficult to measure it accurately. The water current made it difficult to hold the tape measure across the surface of the water which could have affected the accuracy of the data. Due to the flooding of the access routes, we could not get a result for the third sitesHow Problems were overcome: We were careful to ensure that the tape measure was held accurately on the left and right bank. We wore gloves to ensure that our hand were safe from stinging nettles. To make sure that the tape measure was held tightly, we used two or three group members. The third site was flooded so we had to rely on secondary data We chose one person from our group to just focus on data recording to ensure data was recorded accurately.Methodology for Measuring River Depth:Methodology for Measuring River Depth:Link hypothesis: The depth of the river channel increases downstream in the Middle Roding drainage basin.Equipment:Tape measureMetre RulerData recording sheetsMethod:We measured the river depth at each of the sites we visited. We first stretched the tape measure from one bank to the other; this was used as a guide to ensure that we take the measurements in a straight line. It is also a convenient way of measuring the intervals between readings. We held the rigid meter ruler vertically (with its edge facing upstream) in the water to measure the depth of the water, until it just touches the bed of the river. We measured the depth of the river, starting from the left bank to the right bank every 10cm (total of ten depth measurements). We recorded these measurements on a data sheet. This was repeated at each site.

A metre ruler held vertically to measure the depth of the river from the river bed to surface of the river, every 10cm.

Figure 13: Photograph of students collecting depth measurements.

Metre ruler placed vertically to measure the depth from bed to water surface at each tenth.The River Cross section measurement Metre ruler placed vertically to measure the depth from bed to water surface at each tenth

Figure 14: Diagram to show methodology for measuring river depth

Explanation of why data was collected:It was important to measure the depth of the river at each of the three sites to be able to prove or refute my hypothesis that river depth would increase as we moved downstream. Collecting these measurements about the river depth at each of the three sites would show us whether river depth increased as we moved from site A to site C. In addition, collecting the results of the river depth and widths would enable us, to calculate the cross sectional area.Cross sectional area= channel width *channel depthJustification of data collection method:We used a metre ruler to measure the depth of the river at each tenth of the width because this will give us an accurate data. We measured the depth of the river every 10cm because the bed of the river is uneven, so if we had just taken one depth measurement it would have been unreliable. In , taking ten measurements we would enable us to work out the average depth and we will also be able to create a cross section. We used this method as it was simple and easy to collect accurate data.Limitations and Problems:There were some limitations of using this method: The distance and the depth measurements may not have been read accurately due to human errors. It is possible that we might have made few errors in our mental calculation in dividing the width by ten. It was difficult to hold the tape measure accurately at the left hand and right hand bank due to human error and vegetation /stinging nettles. The tape measure did not stay taut due to water current; this affected the accuracy of the measurement. It was difficult to hold the meter ruler across the river due to the water currents. This could have affected the measurement. The user may push the ruler into the sediment when taking the depth the measurement.

The weather conditions were very poor which could have affected the accuracy of data reading and recording. Also, we could not measure the third site due to the flooding of the access routes.How Problems were overcome: We used one member of the group to focus on recording the data accurately. We used a calculator to double check our mental mathematics, this minimized the possible human error. We used two members of our group to make sure that the tape measure was held tightly at the left and right bank. We wore gloves to protect our hands from stinging nettles. We held the ruler with its edge facing upstream, thus reducing the surface area exposed to the water current. It is necessary to reduce the exposed surface area as the water may create a bow-wave and result in inaccurate readings. By positioning the ruler with its narrowest edge facing into the flow it is most resistant to flexing and least able to create a bow wave. We used secondary data for site 3. When taking the depth measurement, we took care not to use unnecessary force when placing the ruler in the water.Methodology for Measuring River Velocity:Link hypothesis: The velocity of the river increases downstream in the Middle Roding drainage basin.Equipment:StopwatchCorkMetre RulerData recording sheetsMethod:We measured the river velocity at each of the sites we visited. We placed the metre ruler horizontally on the surface of the water and used this as a set distance. One member of the group then dropped a cork into the river just behind the metre ruler. As soon as the cork reached the start of the metre ruler, the stopwatch was started. Using the stopwatch, we timed how long it takes the float to travel the length of the metre ruler. This procedure was repeated three times to calculate an average. This was repeated at all three sites.Calculating Velocity: We calculated the average time for the cork to travel the set distance at each site.

Explanation of why data was collected:It was important to measure the velocity of the river at each of the three sites to be able to prove or refute my hypothesis that river velocity would increase as we move from the source to the mouth. Collecting these measurements about the river velocity at each of the three sites would show us whether river velocity increased as we moved from site A to site C. In addition, collecting the results of the river velocity, depth, and widths would enable us, to calculate the river discharge.Discharge = velocity x cross sectional areaE.g. Velocity=5m/s cross sectional area=3m5*3=15 cumecs

Figure15: Diagram to show methodology for measuring river velocity

Limitations and Problems: The cork often got caught on vegetation and bed loads, this caused anomalous result. The float method only shows the velocity at the surface. At the surface wind can affect the results. Possible human error - it was difficult to record the exact time the cork reaches the start/ finish line. The cork might have been thrown or pushed, giving unrepresentative result. In turbulent flow, we found it difficult to see the float.How Problems were overcome: We chose a cork as the float object as it is durable, visible and it is not affected by the wind. The cork was placed in the water before the ruler meter in order to give time to accelerate and make sure it would be travelling at full velocity We repeated measurement three times and took an average; this can reduce the margin of error. We placed the cork upstream and we marked the start and finish lines which helped to minimise the problem. We carefully released the cork into the water without implying any of our force.

Data Presentation and AnalysisFigure 18: Line graph showing the change in water width with distance downstream

Analysis of Figure 18:The graph shows the water width increased with distance downstream. There is a positive correlation between the distance downstream and width of the water however the trend is not constant. The width increases gradually from site A to site B with an increase of only 0.3m over a distance of 700m. From site B to site C, there was an increase of 0.98m over a distance of 700m. The most significant increase in width was between site C and D; there was an increase of 6.82m over the same distance of 700m. From the site (A), nearest to the source (300m) to site furthest downstream (2400m) the water width increased from 0.85m to 8.95m Overall, there was an increase of 8.1m in width over the distance of 2100m.

The result I have collected show clear evidence to prove my hypotheses was right. My hypothesis was: The width of the river channel increases downstream in the Middle Roding drainage basin. We can refute our null hypothesis which was: The width of the river channel does not increase downstream in the Middle Roding drainage basin.Our results also agree with the geographical theories of The Bradshaw Model and The Schumm Model; both the models show that width will increase as we travel downstream. There is an increase in the width downstream due to lateral erosion by the river processes of abrasion, attrition, hydraulic action and collision which widen the channel. The discharge of water in the channel increases due to the tributaries joining the river therefore there is an increased capacity for erosion.

The result for Site D looks like an anomaly because it shows there is such significant increase in width over 700m and not gradual increase that is seen between Site A and C. The reason that this result is an anomaly is because this measurement was secondary data provided by the FSC and they may have collected their data at a different time of the year to us. Therefore there may have been more water in the channel due to weather conditions and seasonal variations which caused more erosion widening the channel.

Site A (300m)Site B (1000m)Site C (1700)Site D (secondary research, 2400m)

Average float time1.4061.231.0963.853

Figure 19: Bar Chart showing the change in average float time with distance downstream

Analysis of Figure 19: The graph above shows that the average float time has increased significantly between Site A and Site D (from 1.046s to 3.853s). This result refutes our hypothesis that velocity increases with distance downstream and also it does not support the theories of the Bradshaw and Schumm Models. However site D might be an anomaly and if we exclude this result, it is clear from the graph that there is a negative correlation between average float time and distance downstream between site A and C. Our data shows that the average float time gradually decreasing between Site A and Site C and this would actually prove our hypothesis and refute our null hypothesis.My understanding of geographical theories and the fact that the average float time did decreased overall between Site A and Site C tell me that the result from site D may be an anomaly. The reason for the anomaly result is because it was difficult to get accurate float time readings as many students were standing in the river channel to take measurements. This may have blocked, diverted or slowed the river flow which has led to unrepresentative data. In addition, we collected our data in the autumn when leaves had fallen from the deciduous trees in the forest and the fallen leave may have blocked the float. Despite of the anomaly result, I believe that my data is sufficient to prove my hypothesis that velocity increased with distance downstream. The reason the velocity increases downstream is because the river is deeper, wider and has higher discharge in its lower course due to the increase water from tributaries. There is less water in contact with the wetted perimeter, so friction from the bed and the banks is minimized. The greater the cross-sectional area in comparison to the wetted perimeter, the more freely the stream will be flowing because less of the water is close to the frictional bed. There also another factor that affects the velocity of water and that is the channel roughness - pebbles, stones and boulders on the beds and banks increase the roughness of the channel. The channel roughness is higher in the upper course and this means the water has to overcome such obstacles and therefore there will be more friction and the velocity of the river is reduced.

Figure 20: Graph to show how river depth increases from left bank to right bank at site A

Figure 21: River cross section at Site A shown by the Inverted graph

Analysis of Figure 20 and 21:

The inverted graph clearly shows how the depth of water changes across the river channel. The inverted graph shows that the river depth increased as you move toward the right bank; the water was significantly deep at the right bank and shallow at the left bank. The reason for this is that site A was on a bend meaning the water will flow faster on the outside of a river bend causing a faster rate of erosion, making the channel deeper and eventually forming a river cliff. The water flows slowly on the inside of the bend and deposits sediments. This part of the channel is shallower and the process of deposition eventually forms a slip-off slope.

Figure 22: Graph to show changes in river depth from left hand bank to right hand bank at Site B

The graph above shows that the river depth remained more or less consistent across the width of the channel showing less variation. The graph shows the river depth is greater at the right hand bank just like Site A and this may have also been due to the faster flow on the outside of the bend causing the channel to be eroded. It also is clear from this graph that the river was slightly deeper in the centre of the channel where the depth reaches its maximum of 0.21m.

Figure 23: Graph to show changes in river depth from left hand bank to right hand bank at Site C

Analysis of Figure 22:The graph above shows that the river depth remained steady across the width of the channel with only small differences. Again, the graph shows that the river depth was greater at the right hand bank and this may have also been due to increased erosion at this point due to faster flow on the outside of the bend. The graph also shows that the river was slightly deeper in the centre of the channel.Figure 24: Graph showing changes in river depth from left hand bank to right hand bank at Site D

The graph above shows that the river depth remained steady across the width of the channel with only small differences. Again, the graph shows that the river depth was greater at the right hand bank and this may have also been due to increased erosion at this point due to faster flow on the outside of the bend. The graph also shows that the river was slightly deeper in the centre of the channel.

Analysis of Figure 25: The graph above shows that the overall average depth increased between Sites A and D and this data supports our hypothesis that river depth would increases with distance downstream. It also supports the Bradshaw model and Schumm Model. The average depth increases from site A to site B with an increase of 0.018m over a distance 700m. From site B to site C, the average depth drops from 0.174m to 0.1276m; the average depth measurement at Site C (1700m downstream) is an anomaly as it shows a decrease in the average depth between Site B and Site C. This refutes our hypothesis and geographical theory. This anomaly may have occurred due to human error; it is likely that there were sediments deposited at the bottom of the channel making the river depth shallower.

Conclusion

In conclusion, the data I have collected are sufficient enough to prove my hypotheses were right. I will go through each of my hypotheses and state whether they were proved or refuted by my data.1.The depth of the river channel increases downstream in the Middle Roding drainage basin.The graphs showing the river depth at each site (Figures 20-24) proved our hypothesis- that river depth would increase with distance downstream. It is clear from the graphs that there is a positive correlation between distance downstream and average river depth. Our data shows that the average river depth gradually increased between Site 1 and Site 4. Site 3, however, was an anomaly as it did not prove our hypothesis and showed an unexpected decrease in depth. This will be discussed in my evaluation. This means that, overall, we are able to prove our hypothesis that river depth increases downstream and refute our null hypothesis that river depth would not increase with distance downstream. These findings supported my own understanding of geographical processes and also support the geographical theories of the Bradshaw and Schumm Models. Depth increases for various reasons, partly because of the increased efficiency of the river meaning that more erosion takes place, enlarging the river channel. This means that the channel has more capacity to carry water. The load carried by the river also increases as we move downstream and this load plays a vital role in eroding and enlarging the channel. It is also true that more water joins the river from tributaries joining the main river and from groundwater flow, throughflow and surface run off.

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