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Determination of the velocity
Velocity of a river/stream/canal varies both vertically and laterally in a given cross
section, it is being minimum at the centre. There are several
methods to determine the velocity as under :
1) Surface floats
2) Sub-surface floats
3) Twin floats
4) Velocity rod or floats
5) Current meter
6) Pilot tube
Surface float and current meter methods are widely used.
Surface float method
Light materials which float on water are floated at a known distance and time
taken to traverse the distance by the float is noted. The velocity of the float is
calculated :
V = Distance travelled by float
Time taken
Fig. 3.1. Surface Float method for measurement of flow of water
The floats are either 'cone' or made up of tight hollow wooden blocks and are
painted. Small flags can be used for identification. Two wire ropes are stretched
across the width of the channel. The first station is on the downstream and
