Question

Which of the following statement is wrong?

(a) Ripples do not occur if the size of the bed particles is coarser than 0.6 mm

(b) Dunes are much larger in length and height than ripples

(c) Crests of both ripples and dunes extend across the entire width of the stream

(d) Ripples are less rounded than Dunes

This question was posed to me in semester exam.

Question is taken from Sediment Load topic in portion Sediment Transport and Irrigation Channels Design of Irrigation Engineering

Answer 1

Correct answer is (c) Crests of both ripples and dunes extend across the entire width of the stream

To elaborate: Both formations of ripples and dunes tend to occur in the form of short-crested waves. Sub-critical flow conditions exist in both these regimes at this stage i.e. Froude’s number is less than unity. Crests of both do not extend across the entire width of the stream.