River Practical Skills (Edexcel IGCSE Geography)

Spec point — 4GE1-S9.128

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

The Bradshaw Model

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

  • 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 means 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 - rivers

Spec point — 4GE1-S9.128

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

  • Quantitative data may include:

    • channel measurements
    • measurements of sediment

  • Qualitative data may include:

    • field sketches
    • photographs

• 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.

Measurement of River Width

• 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 is recorded
• It also allows a mean depth to be calculated for use in the calculation of river discharge

*Depth Measurements *

• 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 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

Positions in River Channel for Velocity Measurements

• 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
  • 10 ÷ 35.43 = 0.282 m/s
  • The surface velocity for site one is 0.282 m/s

Step Four - Discharge

• Discharge = Cross-sectional Area 0.84m²x 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 on by 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)

Exam Hint 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'