Question

For accurate flow measurement in open channels, an arrangement for aeration under the nappe is necessary when the weir used is

• A. Contracted rectangular
• B. Suppressed rectangular
• C. Submerged contracted rectangular
• D. Triangular

Answer 1

The correct option is B

Suppressed rectangular

In a contracted weir (one who’s notch does not span the full channel) the nappe is automatically aerated and springs free of the weir crest. In a suppressed weir (where the sides of the channel act as the ends of the weir notch), the nappe may, or may not, be aerated. So, here the arrangement for aeration under the nappe is necessary.