The correct answer is A. velocity of flow of water.
A current meter is a device used to measure the velocity of water flow. It is typically used in rivers, streams, and other bodies of water to measure the speed of the current. This information can be used for a variety of purposes, such as determining the flow rate of the water, the amount of sediment being transported, and the potential for flooding.
There are a variety of different types of current meters, each with its own advantages and disadvantages. The most common type is the impeller current meter, which uses a rotating impeller to measure the velocity of the water. Other types of current meters include the electromagnetic current meter, the acoustic Doppler current profiler, and the hot-wire anemometer.
Current meters are an important tool for a variety of scientific and engineering applications. They are used in hydrology, oceanography, meteorology, and other fields. They are also used in a variety of practical applications, such as river management, flood control, and water quality monitoring.
The other options are incorrect because they are not the primary purpose of a current meter. Option B, depth of flow of water, is measured by a depth gauge. Option C, discharge, is the volume of water flowing past a given point per unit of time. It is calculated by multiplying the velocity of the water by the cross-sectional area of the flow. Option D, none of the above, is also incorrect.