In Situ Determination of C Value

When all the other variables in the formula are known, solve for C.

This is called calibration.

Hazen-Williams Equation - calculating Friction Head Loss in Water ...

While I could be wrong it sounds like the original poster may be wanting to know how/see what kind of flow coefficient is actually being achieved by their pipeline in the field (not necessarily just someone else's perception/promotion of what a particular pipe would do).

One organization that I know has done a great deal of flow testing of actual pipelines in the field, with cooperation and participation of many utility customers (and incidentally also comparing some different types of ACTUAL/working pipes/pipelines in some systems), is the Ductile Iron Pipe Research Association - see summary discussions of some of such testing on their website at dipra.org.

While I suspect approximations might be had by more simple field means, I suspect DIPRA could provide upon request of a utility etc. more detailed report and/or description of instrumentation and protocols for most accurate field testing.

dhanya, are you looking for a method of calculation (theoretical) or are you looking for a means of measurement (empirical), I.E. a flow meter?

Thanks for the reply,,,,, am lookin for an empirical method.....

I recommend you do a search on flow meters. You will find all kinds for liquid and/or gas. Sonic, turbine, differential pressure etc.