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When it comes to approach conditions for flumes, there can be some question as to what exactly is required.  In this case:  does the approaching flow need to be laminar?

Laminar flow is where the water flows in parallel layers with no disruption between layers.  Envision those arcing water features that you see in hotels and office buildings.  That is laminar flow.  

laminar flow of water

In the field, laminar flow is not going to be present in any channel.  The walls and floors of concrete channels are rough and stream bottoms aren't smooth. Laminar flow is only common in the field when the channel is small and the water is moving slowly.

What you do want to see is that the approaching flow is not turbulent, is well distributed across the channel, and is subcritical. 

 

Image:  NTDTV