To determine the discharge at a section in a stream from its rating curve, the required data are i) slope of water surface at the section ii) stage at the section iii) current meter readings at the section The correct answer is A. (i) and (ii) B. (ii) and (iii) C. only (ii) D. only (iii)

The correct answer is A. (i) and (ii).

A rating curve is a graph that shows the relationship between the stage (depth of water) and discharge (volume of water flowing past a point per unit time) at a particular location in a stream. To determine the discharge at a section in a stream from its rating curve, we need to know the stage at the section and the slope of the water surface at the section. The slope of the water surface is needed to calculate the velocity of the water, which is then used to calculate the discharge.

Option (i) is correct because the stage is needed to determine the slope of the water surface. Option (ii) is correct because the slope of the water surface is needed to calculate the velocity of the water. Option (iii) is incorrect because the current meter readings are not needed to determine the discharge from the rating curve.