Geography • Physical GeographyHard
In fluvial geomorphology, analyze the dynamics of stream load transport, channel hydraulics, and depositional processes: Assertion (A): The capacity of a river to transport sediment load varies exponentially with changes in its flow velocity, typically proportional to the sixth power of velocity according to Airy's Law. Reason (R): A slight reduction in stream velocity due to a drop in gradient leads to a drastic decrease in competence, causing the immediate deposition of the coarsest bed load materials first. Which of the following is correct?
A. Both Assertion (A) and Reason (R) are correct, and Reason (R) is the correct explanation of Assertion (A)✓ Correct Answer
B. Both Assertion (A) and Reason (R) are correct, but Reason (R) is not the correct explanation of Assertion (A)
C. Assertion (A) is correct, but Reason (R) is incorrect
D. Assertion (A) is incorrect, but Reason (R) is correct
💡 Solution & Explanation
According to the sixth-power law of sediment transport formulated by Hopkins and Airy, the mass of the largest particle a stream can transport varies with the sixth power of its velocity, meaning even minor decreases in flow speed drastically diminish competence and trigger the rapid deposition of heavy bedload materials. This principle explains why gravel and boulders drop out first where mountain streams enter plains, forming alluvial fans. Both statements accurately link hydraulic mechanics with sediment sorting.
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