Physical Fieldwork - Epping Forest Flashcards
What is velocity?
The speed of an object in a given direction
What is bedload size?
The magnitude of particles in a river that are transported along the bed
What is channel width?
The lateral extent of the river meanders
What is channel depth?
The distance from the surface of the water to the surface of the river bed
What is ‘downstream’?
The direction towards the mouth of the river, in which the current flows
What was the aim of the investigation?
To explore how river characteristics change with distance downstream along Debden Brook
What was the justification of the aim?
Based on Bradshaw’s Model which predicts the change in river characteristics with distance downstream
Exploration of the truth of these hypotheses and the extent to which we expect each characteristic to change
Where is Debden Brook located?
It is in Essex, near Loughton in South East England and 9km away from Central London
Describe Debden Brook
It is 4km long and has its confluence with the River Roding with the source of the river being Furze Ground
The river covers 7897 acres and is part of the River Thames drainage basin
Why did we choose this location?`
It is close - reducing travel cost and time
Debden Brook is short - easily travel to 3 varying parts of the river in a short amount of time
Safe and accessible - it’s relatively narrow, not too deep and had a workable velocity
What were the subjects of the hypotheses?
Velocity
Channel size (width and depth)
Bedload size
Bedload shape
What was the velocity hypotheses and justification?
Velocity will increase with distance downstream
Increased channel width, depth and multiple tributaries means more water can travel downstream at a quicker rate
This means there is less contact with the river bed and less energy used to overcome friction
What was the channel width hypotheses and justification?
Channel width will increase with distance down stream
Due to lateral erosion which forces particles laterally into the river bank, widening it
What was the channel depth hypotheses and justification?
Depth will increase with distance downstream
Because of vertical erosion which forces particles vertically into the river bed, lowering it
What was the bedload shape hypotheses and justification?
Particles will become more spherical in shape with distance downstream
The constant erosion (attrition, abrasion, saltation and traction) of the particles will make them more round in shape
What was the bedload size hypotheses and justification?
Bedload size will decrease with distance downstream
The repeated erosion will wear away the particles, decreasing their size
What is the teacher risk assessment of drowning?
Concern: teacher
Risk: low
Consequence: death or injury
Prevention: ensure river is shallow, students can swim or are supervised and wearing appropriate footwear
What are the factors to consider when preparing a risk assessment?
Hazard / event
Concern of who?
Risk level
Consequence
Action to be taken to reduce risk
Action to be taken in event of occurrence
What is the student risk assessment for drowning?
Concern: student
Risk: low
Consequence: injury or death
Prevention: listen to instructions (eg: when to get in or out) and wearing appropriate footwear for walking in a river
In case of the event: alert a teacher who will call 999
What is the risk assessment for a crash for travelling to the location?
Event: crash
Concern: teacher
Risk: low
Consequence: injury or death
Prevention: choosing a reputable coach company
In case of event: call 999 and find a safe location to stand and wait for help
What is the risk assessment of Weil’s disease?
Concern: student
Risk: low
Consequence: sickness
Prevention: avoid drinking river water, cover wounds with blue tape and wear gloves
In case of event: go to the hospital
What is the risk assessment for slips, trips and cuts?
Concern: student
Risk: medium
Consequence: injury (cuts)
Prevention: walking slowly, wearing willies to reduce likelihood of cuts and watching where you walk
In case of event: use a first-aid kit to clean up and then apply a plaster
What is the risk assessment for crossing the road?
Event: being hit by a car
Concern: teacher
Risk: medium
Consequence: injury or death
Prevention: follow the FSC road crossing protocol
In case of event: call 999
What is the risk assessment for the weather?
Concern: student
Risk: medium
Consequence: wet clothes, fever (too cold or too hot)
Prevention: wear sensible clothing and bring spare clothing
What is methodology?
How data is collected (ie: data collection)
How was the depth of Debden Brook measured?
Tape measure held taut to measure the width of the river
Depth taken at 1/4, 1/2 and 3/4 across the width of the river
Depth was measured with a 30 cm rule perpendicular to the surface and noted down in metres
Why was the depth of the river measured this way?
To measure the cross-sectional area
Which allowed us too see whether the depth of the river changed with distance downstream
What were the benefits of measuring the river depth this way?
Simple method to use
Allows a depth measurement at 3 points (easily spot anomalies and can draw a cross-sectional diagram)
Allows for a comparison of different sites downstream
What were the drawbacks of measuring river depth this way?
Human error in measurements could skew results
3-point cross-section is too limited of a data range
Shallow river was difficult to measure
How was the width of the river measured?
Tape measure used to measure from river bank to the other river bank
Tape measure was held taut to improve the accuracy and precision of reading
Why was the river width measured this way?
To see whether the width of the river changed downstream using accurate results
What are the benefits of measuring channel width this way?
Allows for clear comparison of different measurements in different sites
Allows accurate data to be collected to make conclusions
What are the drawbacks of measuring channel width this way?
Human error could skew results
How was the velocity of Debden Brook measured?
Place the metre rule on the river bank and drop a cork by the start of the ruler
When the cork passes the start of the ruler, start the stopwatch
Stop the stopwatch when the cork reaches the end of the ruler
Calculate the velocity by dividing the distance (1 m) by the time taken
Repeat 2 times and work out an average
Why was the velocity measured this way?
To see if the velocity of the river changes downstream
What are the benefits of measuring the velocity this way?
An effective way of seeing whether the velocity increases or decreases
A simple but effective way to calculate velocity
Average allows anomalies to be ignored
What are the drawbacks of measuring the velocity this way?
Human measurement error due to reaction time
How was sediment size measured in Debden Brook?
Scoop out some bedload into a plastic pot
Take out any dangers (such as glass or plastic)
Pick out 5 samples randomly
Measure the longest part of each sample with a 30 cm ruler
Why was sediment size measured this way?
To allow us to see if the sediment size of the river changed downstream
What are the benefits of measuring sediment size this way?
It is simple and effective
What are the drawbacks of measuring sediment size this way?
Bias towards samples (if not picked randomly) can skew results
How was sediment shape measured in Debden Brook?
Using the 5 samples used to measure sediment size, researchers should use their own judgement to compare the roundness, smoothness and sphericity with that of those on the diagram given
Why was sediment shape measured this way?
To see how the rate of erosion and the shape of sediment changes downstream
What are the benefits of measuring sediment shape this way?
Quantified so it is easily comparable
Clear scale to compare all stones against (standard comparison)
What are the drawbacks of measuring sediment shape like this?
Very subjective which could lead to misleading results
How was channel depth and width presented?
Using cross-profiles showing the cross-sectional area
How was data on the velocity of Debden Brook presented?
Using proportional arrows for velocity
How was sediment size presented?
Using a bar chart to show sediment size
How was sediment roundness presented?
Using a 100% bar graph to show bedload shape
How was the relationship between sediment size and roundness shown?
Using a scatter graph
Why was a cross-profile used to show the channel width and depth of Debden Brook?
To show visually and clearly the area that we are investigating
To easily see how channel depth and width changes with distance downstream
To easily compare with the 2 other sites
Why were proportional arrows used to show the velocity of Debden Brook?
Proportional arrows can be easily compared to clearly see the difference in river velocity in the upper course, middle course and lower course
Why were bar charts used to present the change in sediment size?
It is a widely-understood method of presenting data
It is most suitable for the non-continuous data we have
Why was a 100% bar graph used to show bedload shape / roundness?
It is easily comparable which is useful when judging the relative roundness of bedload in the upper, middle and lower course of Debden Brook
Why was a scatter graph chosen to highlight the relationship between sediment size and sediment roundness?
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What are the benefits of presenting channel width and depth as cross-profiles?
They are very clear - not cluttered
Easily comparable
What are the benefits of presenting velocity as proportional arrows?
Good visual representation of data
Shows spatial difference which is helpful when considering where velocity increases the most
The scale allows for easy comparison
Arrows show movement clearly
What are the benefits of using bar charts to show sediment size?
It summarises a large dataset in visual form which is easier to analyse
Clarifies trends better than tables do
Can estimate / pinpoint key values at a glance
Bar charts are easily understood due to their widespread use in business and the media - conclusions can be verified and checked by others easily
What are the benefits of using a 100% bar graph to show bedload shape?
`It is easy to compare the roundness of the sediment and which, on average, appeared more in the different stages of the river
Works well visually
What are the benefits of using a scatter graph to highlight the relationship between sediment size and sediment roundness?
A correlation can easily be identified as positive, negative, strong and weak
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What are the drawbacks of using a cross-profile to show the change is channel size?
Only shows a snapshot at a given time when, in reality, the place depicted can change
Cannot be very accurate due to the limited amount of measurements taken
Not easy to quantify the changes in channel depth and width downstream
What are the drawbacks of using proportional arrows to show the change in velocity?
The scale needs to be correct so the symbols fit - difficult to draw / present
Too many arrows can be difficult to interpret
Size of the arrow may obscure the location making it difficult to read
What are the drawbacks of using bar charts to present a change
Re-ordering bars can change the interpretation due to assumptions made at a glance?
Can easily compare adjacent data but not data that are not neighbours
Bar graphs are not good at displaying continuous data
Can easily be manipulated to give a false impression of a data set
Using too many bars can clutter the chart and make it difficult to read
What are the drawbacks of using a 100% bar graph to show bedload roundness?
Readers do not know the sample size and therefore do not know if the results were taken from a large enough pool to be accurate
Can be easily skewed based on the small sample used
What are the drawbacks of using a scatter graph to show the relationship between sediment size and roundness?
?
What is the analysis of the cross-profile showing the cross-sectional area?
Width and depth of the river channel increase as you travel downstream
Shortest width was 1.23 m and the longest was 2.95 m
At site 1 (the uppercourse) the deepest point is in the middle which is expected as vertical erosion is most prominent there
We expected a shallow depth which we did as the deepest point was only 6 cm
What is the analysis for proportional arrows for velocity?
Velocity increases downstream
The mean velocity in the upper course of Debden Brook 0.07 m/s and it increased significantly in the lower course to 0.26 m/s
There was an anomaly as the mean velocity in the middle course was higher than that of the lower course at 0.31 m/s
This is because we went further down the river for the last site as other people created a make-shift dam so our results are not accurate
Also, speed doesn’t necessarily increase with channel size (other factors such as vegetation and disruption from river bed)
What was the analysis for the bar chart which showed the size of sediment?
Sediment size does decrease downstream as expected
Upper course had a median sediment size of 5.48 cm on its long axis compared to the lower course median of 2.26 cm (more than half the size)
There are no clear anomalies
But there is a large range if sediment sizes in the upper course (4.58 cm) considering the placement of the stones (some were towards the bottom and thus were vertically eroded more)
What was the analysis for the 100% bar graph that shows the shape of bedload?
It becomes rounder - agrees with hypotheses
All sediment in the lower course was at maximum roundness (5) but there were anomalies in the upper course as there was a piece of sediment already at maximum roundness (5) and others at 2
Perhaps the subjective method for quantifying this measurement caused the large discrepancies
What are the conclusions from the inquiry?
Channel size does increase downstream as shown by Bradshaw’s model and our data
Velocity does not increase downstream which goes against Bradshaw’s model, result most likely disrupted by location chosen
Bedload size increases and gets rounder downstream as expected, shown by our data
However, these conclusions may not be justified or accurate because:
- there was not enough data taken - there may be truth to out anomalies and extreme values could have skewed our results
- we need to use a bigger river where the trends will be more apparent in spite of anomalies
What relationship did the Spearman’s rank between the sediment size and shape show?
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What were the strengths of our inquiry?
Each course was accessible so we could collect data
The river wasn’t too deep so it was safe
Methods were easily practised in the river without being time-consuming (efficient)
What were the weaknesses of our inquiry?
Lots of people in the river at one time could have skewed results
Was very hot so water evaporated - our results were not representative of the river normally
Vegetation often prevented access to some parts of the river preventing us from collecting more data
Was a mall river, in larger ones, difference in data in the three courses would’ve been more apparent - our conclusions aren’t really justified as the difference is too small
What were the opportunities as a result of our inquiry
We are now able to carry out more tests like this to evaluate the truth in theory and hypotheses
We can critically analyse secondary data used to draw conclusions
What were the threats to our inquiry?
Rain could dramatically change results
Evaporation could occur due to the heat which can alter results
