River Practical Skills (Edexcel IGCSE Geography)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
River Practical Skills
River Fieldwork Enquiry
To undertake a river fieldwork enquiry there are a range of practical skills and methods that will be used
These can be applied to any river fieldwork
The fieldwork enquiry should be linked to geographical theory
In the river fieldwork enquiry the Bradshaw model is usually used
Aims and Hypothesis
The aims and hypothesis come from questions asked about the river such as:
Does discharge increase along the length of River Y?
Does the average velocity increase along the length of River Y?
How and why does the cross profile change along the long profile of River Y?
Examples of an aim would be:
An investigation into how a river's cross-profile changes downstream
An investigation into changes in discharge with distance downstream
Examples of a hypothesis would be:
The width and depth of River Y will increase with distance downstream
The discharge of River Y increases with the distance downstream
After the aims and hypothesis of the fieldwork have been established the next steps include:
Selecting the sites - this will involve sampling
Deciding on the equipment to be used
Considering any health and safety issues - completing a risk assessment
Data collection method
Worked Example
(i) Suggest one possible aim of a river channel investigation
(2 Marks)
Answer: This should be an aim, not a hypothesis so should outline what the enquiry/investigation is attempting to achieve
To investigate the changes in velocity (1) with increasing distance from the source (1)
To investigate the changes in channel cross-profile (1) with increasing distance from the source (1)
An investigation into changes in river discharge (1) after confluences within the river (1)
(ii) Identify three reasons why a river channel investigation may not achieve the aim given in (i) (3 Marks)
Answer:
Data inaccurate (1)
Insufficient data collected (1)
Inaccurate data analysis (1)
Human errors in data recording (1)
Aim not practical (1)
Unsuitable sites selected (1)
Site Selection and Sampling
To collect data it is not practical to measure all parts of the river
To select the river sites sampling should be used to reduce bias
There may be situations where access to the river is limited meaning an opportunistic approach to sampling may need to be taken. However, this should be as close as possible to the site selected using sampling
The most commonly used sampling strategies for a river enquiry are:
Systematic - a sampling of sites at regular intervals mean that all parts of the river are covered
Random - the use of random sampling means that all sites have an equal chance of being selected which eliminates bias
Stratified - by sampling sites immediately downstream of a confluence significant changes in discharge can be identified
Site location can be recorded using GPS to give an accurate location using latitude and longitude
Worked Example
Suggest which sampling method would be appropriate to use in a river channel investigation
(3 Marks)
Answer:
Systematic because measuring at regular intervals (1) ensures that no parts of the river are missed (1) and it reduces bias (1)
Random because using a random number generator (1) means all sites have an equal chance of being selected (1) which means that there is no bias (1)
Equipment
To complete the river measurements a range of equipment is needed
The equipment includes the following:
25+ meter tape to measure the river width and for marking out distance downstream for velocity measurements
1-metre rule for measuring the depth
Clipboard for holding recording sheets
Pencil for writing in data
Camera to take photographs of sites and river features
Float or flowmeter for measuring velocity
Stopwatch if not using a flowmeter
Worked Example
Identify a suitable piece of equipment to measure river velocity
(1 Mark)
| A Anemometer |
| B Quadrat |
| C Clinometer |
| D Stopwatch |
Answer:
D (1) - Stopwatch which is used to time how long it takes a float to cover a specified distance
Risk Assessment
Any fieldwork will involve consideration of health and safety using a risk assessment
Risks associated specifically with river fieldwork may include:
Weather conditions
Slippery rocks
Polluted water
Working in an unfamiliar place
Misuse of equipment
Worked Example
A group of students has investigated the changes in a river channel shape.
State one risk that the students might identify in their risk assessment
(1 Mark)
Answer: Any one of the following would be acceptable
Slip or fall (1)
Infection from dirty water (1)
Flash flooding (1)
Weather conditions (heavy rain/sun) (1)
Suggest one way the risk stated could be managed
(1 Mark)
Answer: This should follow from the answer above
Sturdy/suitable footwear e.g. walking boots (1)
Wash hands/use antibacterial hand wash/cover cuts and wounds (1)
Do not enter the river after heavy rainfall (1)
Check the weather forecast before going out to collect fieldwork data (1)
Using Equipment in the Field
Data Collection Methods
The data collection methods will depend on the aims/hypothesis of the fieldwork
The starting point with most river fieldwork is to measure the width and depth
Data collection should include both quantitative and qualitative methods
The collection of quantitative data can be completed in several ways in a river study
Width
The measurement of width is taken where the water surface comes into contact with the river banks.
To take an accurate measurement:
Measure from the point where the dry bank meets the water on one side to the point where the dry bank meets the water on the opposite side
Ensure that the tape is held taut and does not touch the water this could affect the reliability of the data
Depth
The measurement of depth should be completed at regular intervals across the width
This ensures a full picture of the changes in depth across the whole channel width are recorded
It also allows a mean depth to be calculated to use in the calculation of river discharge
To take an accurate depth measurement:
Work out the distance apart each depth measurement needs to be
Place a meter rule into the water at the correct point
Ensure the meter rule is placed sideways on with the flat side facing the banks - this reduces any impact on the water height ensuring more accurate measurements
Record the distance from the bed to the surface of the water
Repeat this across the width of the river
Velocity
The velocity is the speed at which the river flows
This can vary across the channel width as well as along the course of the river so velocity should be recorded in three positions - towards the left bank, centre and towards the right bank
Using a flow meter velocity can be easily measured by:
Taking readings at three equal distances across the river width
Placing the flow meter into the water at least 3cm below the surface
Three readings should be taken at each of the three places across the channel to allow the calculation of a mean
To take an accurate measurement using a float:
Measure a set distance upstream - for example, 10 meters
Drop a float at the start of the 10 meters
Time how long it takes for the float to travel the distance using a stopwatch
Repeat at each position three times to allow the calculation of a mean
Discharge
The discharge of the river is calculated rather than measured
The first step is to calculate the cross-sectional area:
Cross-sectional area (m2) = width (m) x mean depth (m)
The second step is to calculate the velocity:
If a flow meter the mean velocity should be calculated by adding the velocity measurements and dividing by the number of measurements
If a float has been used and a distance of 10m then the meantime should be divided by 10 to calculate the time taken to travel 1m
Discharge (m3/s) = cross-sectional area (m2) x velocity (m/s)
Worked Example
Calculating Discharge
Step One - Depth
Calculate the mean depth
All units of measurement should be the same
The mean depth should be calculated in meters not centimetres
Depth measurements for Site One
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | Mean |
|---|---|---|---|---|---|---|---|---|---|
Depth in m | 0.05 | 0.12 | 0.17 | 0.23 | 0.30 | 0.35 | 0.28 | 0.18 | 0.21 |
To calculate the mean depth add the 8 measurements together and divide by 8
This gives a measurement of mean depth = 0.21m
Step Two - Cross-sectional area
Cross-sectional area (m2) = width (m) x mean depth (m)
If the width is 4m x mean depth 0.21m the cross-sectional area = 0.84m2
Step Three - Velocity
Time Measurements for Site One
Time measurement | Left | Centre | Right |
|---|---|---|---|
1st | 35 | 28 | 37 |
2nd | 42 | 30 | 39 |
3rd | 36 | 27 | 45 |
Mean | 37.7 | 28.3 | 40.3 |
To work out the mean time taken for the float to travel 10 metres for site one the following calculations need to be completed:
37.7 + 28.3 + 40.3 = 106.3
106.3 is then divided by 3 (number of positions) to give a mean time for site one of 35.43 seconds
Divide this by 10 to get the velocity in m/s
35.43/10 = 3.543 seconds
The surface velocity for site one is 3.543 m/s
Step Four - Discharge
Discharge = Cross-sectional Area 0.84m2 x Velocity 3.543 m/s
Discharge = 2.98 m3/s (cumecs)
Photographs and Field Sketches
Photographs and field sketches are qualitative data
Just as with any data collection and presentation they have strengths and weaknesses
In a river enquiry photographs and field sketches can be used to show landforms and particular features such as bed load
Photographs are also ideal for illustrating the data collection methods used
Worked Example
During a geographical enquiry exploring changes in a river, channel students completed annotated field sketches as part of their data collection.
Suggest two advantages of this technique
(4 Marks)
Answer:
Students can get a quick view of the areas they are working recording key features (1) to support recall later (1)
Students can highlight features (1) that they want to focus on as part of their study (1)
Examiner Tips and Tricks
Annotations and labels are not the same. A label is a simple descriptive point. For example, 'meander'. Whereas an annotation is a label with a more detailed description or an explanatory point. For example, 'slip off slope where the material has been deposited due to slower flow'
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