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River Run
Cambridge IGCSE Geography 0460 EXAM YEARS 2027-2029 The Bradshaw Model
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The Bradshaw Model: how rivers change downstream
This free game is part of our Cambridge IGCSE Geography (0460) course for exams in EXAM YEARS 2027-2029.
What is the Bradshaw Model?
The Bradshaw Model shows how the characteristics of a river change as you travel from its source to its mouth. It is one of the most important models in IGCSE Geography river studies and a favourite for fieldwork questions.
In River Run, you fly a survey drone to three sites: the upper course, middle course and lower course. At each one you predict what has changed, take measurements, and build up the Bradshaw Model yourself.
What increases and what decreases downstream?
- Increase: width, depth, discharge, channel efficiency, velocity (usually) and the cross-sectional area of the channel.
- Decrease: gradient (the slope gets gentler), load particle size and channel roughness. Load also becomes more rounded and better sorted.
Velocity is the one that surprises students. Even though the gradient gets gentler, velocity usually increases because the wider, deeper channel is more efficient, with less friction from the bed and banks.
Calculating discharge
Discharge = cross-sectional area × velocity, where cross-sectional area = width × depth. Discharge is measured in cumecs (cubic metres per second, m³/s).
Velocity can be measured in fieldwork with a float: velocity = distance ÷ time. For example, a float that travels 10 m in 6.7 seconds has a velocity of about 1.5 m/s. A common mistake is to add the measurements instead of multiplying them. Always multiply all three.
Load: attrition and abrasion
As rocks are carried downstream, attrition (rocks knocking into each other) and abrasion (rocks scraping the bed and banks) make them smaller and rounder. In fieldwork, the Powers Scale of Roundness is used to record how rounded the stones are.
Evaluating the model
The Bradshaw Model is a useful simplification, but real rivers do not always follow it. Dams, channelisation, tributaries, bands of hard rock and waterfalls can all break the pattern. In the exam, good evaluation explains why a real river might not match the model.
Frequently asked questions
What does the Bradshaw Model show?
How river characteristics change from source to mouth. Width, depth, discharge and velocity increase, while gradient and load particle size decrease.
Why does velocity increase downstream?
The channel becomes wider, deeper and smoother, so it is more efficient and less energy is lost to friction, even though the gradient is gentler.
How do you calculate river discharge?
Multiply width × depth to get the cross-sectional area, then multiply by velocity. The answer is in cumecs (m³/s).
Why does the load get smaller downstream?
Attrition and abrasion break the rocks down and round them off as they are transported.
Is River Run free?
Yes. The game is free to play in your browser, with no sign-up. It covers river processes and the Bradshaw Model in the Cambridge IGCSE Geography course.