This causation covers Why Each Bradshaw Variable Changes: The Cause Chain within Physical Geography Fieldwork for GCSE Geography. Revise Physical Geography Fieldwork in Fieldwork for GCSE Geography with 13 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 3 of 16 in this topic. Use this causation to connect the idea to the wider topic before moving on to questions and flashcards.

⛓️ Why Each Bradshaw Variable Changes: The Cause Chain

Understanding the reason for each change is essential for exam questions that ask you to "explain" or "suggest why". Here is the chain of causes that drives the model:

More tributaries join as you move downstream — every time a smaller stream (tributary) joins the main channel, it adds water to the flow. This means discharge (the volume of water passing a point per second, measured in cumecs — m³/s) consistently increases downstream.

Greater discharge produces a larger channel — the increased volume of water has more energy, which drives both lateral erosion (widening the channel) and vertical erosion (deepening it). Over time, the river carves a bigger cross-section.

A larger, smoother channel has less friction — in the upper course, the river flows over a rough, rocky bed with steep banks. In the lower course, the channel is wider and the bed is lined with finer, smoother sediment. The hydraulic radius (the ratio of water volume to channel contact) increases, meaning less energy is lost to friction per unit of water.

Less friction means greater velocity — this surprises many students, who assume rivers must slow down as they get bigger. In fact, because efficiency increases faster than size, downstream rivers are typically faster than their upper-course counterparts despite having a gentler gradient.

More energy means more erosion and transport of sediment — the increased velocity and discharge give the lower course more energy to transport and rework sediment, including the pebbles and particles carried from upstream.

Transport breaks down pebbles over distance — as pebbles travel hundreds of kilometres from upland sources, attrition progressively reduces their size and increases their roundness. By the lower course, the coarse angular boulders of the upper course have been worn down to small, smooth, rounded pebbles.

Practice questions for Physical Geography Fieldwork

A student drops an orange into a river and times how long it takes to travel 10 metres. Which variable are they measuring?

A. Channel depth
B. River velocity
C. Cross-sectional area
D. Bedload size

1 markfoundation

Describe how you would use the float method to measure river velocity at one site. Include how you would improve the reliability of your results.

3 marksstandard

Why Each Bradshaw Variable Changes: The Cause Chain

⛓️ Why Each Bradshaw Variable Changes: The Cause Chain

Practice questions for Physical Geography Fieldwork

Quick recall flashcards

13 questions on Physical Geography Fieldwork — practise free