A Parshall flume needs a minimum aproaching canal lenght that is straight and free of obstacles.
What is that lenght??
How do i calculate it?
Data: Flow range= 2000-4000 m3/hora
Parshall throat width= 3 feet
You can find that length in Stevens Water Resources Data Book or possibly in Kings Handbook of Hydraulics. You may also be able to get that information from your flume supplier.