River Discharge: How to Calculate the Discharge Flow of River

(Last Updated On: 01/09/2017)
For various purposes, the Measurement of River Discharge is required in Dam Engineering. It requires a lot of Skill, Accuracy, and also Education.
river discharge method
  • So, To Measure the River Discharge, we require

01) Area of Flow
02) Average Velocity of Flow.
 
With this Data, we can calculate

River Discharge

River Discharge = Area of Flow X Average Velocity of Flow.
 

So, To Calculate Area of Flow of River Discharge, we can use following Methods

 
  • Simple Segment Method to Calculate River Discharge

In this Method, the whole Width of River is divided into a number of Segment at Length, say L1, L2, L3 (Length of Segments) and at Depth say d1,d2,d3 (mean Depth of Segment).
Now, the Area of Flow is Sum of all Area of Segments.(L1d1+L2d2+L3d3………………)
 
  • Simpson’s Rule for River Discharge

In this Method, the whole Width of River is divided into an even number of equal Segments, so that there is an odd number of Depths taken at the end of each Segment.
 
  • Average Velocity of Flow

To Measure Average Velocity of Flow following are three important Methods we can use.
A) Floats
 
  • Floats

With the help of Single Float, the Surface Velocity, at any section of River can be easily obtained. Hence For this, we have to count the time taken by the Float to Travel known Distance.
The Velocity is Calculate by dividing the distance traveled by the Float by the time taken to travel that distance.
This Surface Velocity is then converted into an Average Velocity. To obtain Average Velocity directly, a Double Float or Rod Float is used.
 
  • Double Float

It consists of two Floats connected by a Wire or String. One Float is a Small Wooden Float, which Floats on Surface of River.
Another is a Hallow Metallic Sphere which is heavier than Water is suspended from the former by a Wire or String, connecting the two Floats, in such that, the Lower Metallic Float is at Depth of 6/10 of the Total Depth of Flow, as the Average Velocity of Flow exists at a Depth of 6/10 to the Total Depth.
The Velocity of Flow then Calculates by Dividing the distance traveled by the Float by the time taken to travel that distance. This Method Directly gives the Value of Average Velocity.
 
  • Rod Float

It consists of a Wooden Rod or a Metallic Rod Weighted at the bottom, so as to keep it Vertical or Inclined while traveling.
The Length of the Rod is so adjusted that it should not touch the Weeds at bottom of the River and its top should be above the Water Surface.
A Telescope Rod may also be used to suit different Depths. A section free from Weeds must be chosen to avoid possibilities of the Weeds at the bottom of River to Interface with Rod Float.
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