Physical Fieldwork: Data Collection

Physical fieldwork is a core requirement of the Edexcel B GCSE Geography specification. You must carry out at least one investigation in a physical environment — typically a river or coastal study. This lesson focuses on the practical skills of data collection in physical geography fieldwork: the equipment you need, the measurements you take, and the techniques you use to ensure your data is accurate and reliable.

Whether you studied a river or a coastline, you need to be able to describe and explain your data collection methods in detail. The exam will test your understanding of why each measurement is taken, how the equipment works, and what could go wrong.

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River Fieldwork: Key Measurements

River studies are one of the most common types of physical fieldwork for GCSE Geography. You typically investigate how the river changes downstream, testing predictions from the Bradshaw model.

Measuring River Width

What it measures: The distance across the river channel from one bank to the other at the water's surface.

Equipment: Tape measure (or measuring tape stretched across the channel), ranging poles.

Method:

1. Stretch a tape measure across the river at right angles to the flow
2. Secure each end on the bank using ranging poles or by having a person hold each end
3. Read the distance in metres at the water's edge on each bank
4. Record the measurement to the nearest 0.1 metre

Key considerations:

• Ensure the tape is taut and level — sagging will overestimate width
• Measure at right angles to the flow, not diagonally
• Take measurements at the same relative position at each site (e.g. the widest point, or a straight section away from meanders)

Measuring River Depth

What it measures: The vertical distance from the water's surface to the riverbed at multiple points across the channel.

Equipment: Metre ruler or depth pole (ranging pole with measurements marked), tape measure across the channel.

Method:

1. With the tape measure already stretched across the river, take depth readings at regular intervals across the channel (e.g. every 0.5 metres or every 1 metre)
2. Place the ruler vertically into the water until it touches the riverbed
3. Read the depth at the water's surface level to the nearest centimetre
4. Record each depth measurement along with its distance from the left bank

Key considerations:

• Keep the ruler vertical — tilting it will overestimate depth
• On rocky riverbeds, take the reading from the top of the substrate, not from crevices between rocks
• Multiple depth readings can be used to calculate the cross-sectional area of the channel

Calculating Cross-Sectional Area

The cross-sectional area tells you the size of the river channel at a particular point. It is calculated from width and depth measurements:

Cross-sectional area (m²) = width (m) x average depth (m)

A more accurate method is to divide the cross-section into segments and calculate the area of each:

Distance from left bank (m)	Depth (m)
0.0	0.00
0.5	0.12
1.0	0.25
1.5	0.31
2.0	0.28
2.5	0.15
3.0	0.00

Each segment area = interval width x average depth of the two sides. Sum all segments for the total cross-sectional area.

Exam Tip: You may be asked to calculate cross-sectional area from a data table in the exam. Practice the calculation: multiply the width of each segment by the mean depth of its two edges, then add the segments together. This is more accurate than simply multiplying total width by mean depth.

Measuring River Velocity

What it measures: The speed of water flow, usually in metres per second (m/s).

Equipment: Flow meter (digital or impeller type), or a float (e.g. an orange or dog biscuit) and stopwatch, tape measure.

Method A — Flow Meter:

1. Place the flow meter in the river with the impeller facing upstream
2. Hold it at 0.6 x depth below the surface (this gives the average velocity for the water column)
3. Allow the reading to stabilise and record the velocity in m/s
4. Take 3–5 readings at each point across the channel and calculate the mean

Method B — Float Method:

1. Measure a straight section of river (e.g. 10 metres) using a tape measure along the bank
2. One person releases the float upstream at the start point
3. Another person times how long the float takes to travel the measured distance
4. Calculate velocity: velocity (m/s) = distance (m) / time (s)
5. Repeat 3 times and calculate the mean
6. Multiply by 0.85 (a correction factor, because the float measures surface velocity which is faster than the average velocity of the whole water column)

Method	Accuracy	Equipment Cost	Ease of Use
Flow meter	High — measures at correct depth	Expensive (£100+)	Moderate — needs calibration
Float method	Low–Medium — only measures surface velocity	Very cheap (an orange costs pennies)	Easy — simple equipment

Exam Tip: If using the float method, always mention the 0.85 correction factor. Examiners want to see that you understand that surface velocity is faster than mean velocity because friction with the bed and banks slows deeper water.

Measuring Discharge

Discharge is the volume of water passing a point in the river per second, measured in cumecs (cubic metres per second, m³/s).

Discharge (m³/s) = cross-sectional area (m²) x mean velocity (m/s)

This is a calculated value, not a direct measurement. You need both cross-sectional area and velocity data to calculate it.

Measuring Sediment Size

What it measures: The size of stones and pebbles on the riverbed.

Equipment: Ruler or callipers, pebble sizing chart (Powers' scale of roundness), recording sheet.