CHAPTER 10 - CURRENT METERS

11. Method of Measurement

Depth sounding, either with a meter and rod assembly or with a special sounding line and weight, should first be made at each of the permanent measuring points. These depths should be properly recorded. Next, the mean velocity at each of the measuring points should be determined with the current meter by one of the methods listed in the following section. Velocity measurements should be properly recorded.

Errors of velocity measurement will arise if the current meter:

• Is placed closer to the boundary than 1-2 rotor diameters
• Is used to measure velocities less than 0.5 ft/s or out of the range of calibration. Overdriving the rotor can damage bearings
• Is not held steady in one position during the time measurement
• Is used in significant waves, such as those caused by wind
• Is used in flow which is not parallel to the axis of the propeller meter or is oblique to the plane of the cup-type meter
• Is impeded by weeds or debris