ANS:B - 1.5%

The discharge Q over a rectangular weir can be calculated using the weir equation: Q=C×L×H^3/2 Where:

• Q is the discharge,
• C is the discharge coefficient,
• L is the width of the weir crest,
• H is the head of water over the crest of the weir.

Let's consider the effect of a 1% error in measuring the head of water (H). If H is the correct head and ′H′ is the measured head with a 1% error, then: H′=H+0.01H=1.01H Now, let's find the change in discharge due to the error in head measurement: Q'-Q/Q ​ =C×L×(1.01H)^3/2−C×L×H^3/2​ / C×L×H3/2 =(1.01)3/2−1 / 1 ​ ≈1.0151−1/1 ≈0.0151This is approximately 1.51%. So, the closest option is 1.5%.