Velocity Gradient for Flow Over Weir in Open Channel

The velocity gradient considered for flow over weir is 800 to 1000 / sec.

How do we get this value?

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• Flowmetering
• River Engineering
• Dams
• Surface Flow Analysis
• River Engineering
• Flow Meters

6 Answers

1. My question is what is the optimum value of this gradient and why ?

2. Gradient velocity is a function of Flow over weir and Power which shall be calculated based in pressure  drop in the weir. Regards.

   1 Comment

   1. My question is - what is optimum value of gradient & why ?

3. Hi, you need to know the geomterical of the weir as well (upstream and downstream slope, height, length).

   You can also use hydraulic jumps formula to simplify calculation for an approach. The parameter you can acquire is the water depth and weir height which resulting those gradient flow regimes.

4. Hi. SP.Gdevng. pl expand.. what is the 1st parameter per second.. Is it flow in liters or velcity on metres per sec.. then area of weir section to be gien.pl.. w wshs .. Prof Ajit Seshadri Vels University. Chennai. INDIA .. 

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   1. Good morning Professor Seshadri !

      The the value mentioned is a range of gradient i.e 800/sec to 1000 per sec.

      The question is: Why is velocity gradient usually considered as 800-1000 /sec for flow over rectangular sharp crested weir in a rectangular open channel, having free flow of water.

      How do we arrive at this value ?

      Is this value related with having a laminar flow in a raw water channel ?

      Do we have any ref of empirical relationships which support the reasoning to consider velicitygradient in the range of 800/sec to 1000 /sec. 

5. https://nptel.ac.in/courses/105106114/pdfs/Unit14/14_3b.pdf

   1 Comment

   1. Thank You John !

      Will go thru the pdf...

6. HI-Sandeep,Velocity gradiant is measure of relative velocity of two particles of fluid and distance between.To overcome the shearforce velocity gradiant is mandatory.The value we will get is V/Distance.The verticle fall of water the wier is at least minimum value to ensure sufficient turbulance.Assume that mixing time 2-4 sec after the weir then velocity gradiant is expected 800-1000/s

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   1. Thank You Mohammed for your response.

      I am aware of the meaning of velocity gradient. The question is why 800-1000/sec is suggested as  normal ?what is the impact if tV.G is considered as 500 or 1500 ?