Water flow in trough / channel

[icw]

Need to allow water to flow in an open stainless steel U shaped trough tilted at an angle of 1:5 at a flow rate of 8 litres per second.

Question: What are the profile dimensions of this trough which is 2 metres long? or better still, what is the calculation?

 

[butelja]

Calculate the hydraulic diameter, which is D_h = 4*A/P. A is cross sectional area of the fluid in the trough. P is the wetted perimeter, which is the portion of the perimeter of the fluid that is touching the trough. Once this is done, you can calculate the Reynold's number and use friction factors from a Moody chart. Equate you trough slope to the hydraulic gradient, and find the flow rate by itteration. However, for such a short trough, there may be significant entrance and exit effects that I'm not sure how to handle.

 

[icw]

Thanks butelja, I work with pipe frictions a fair bit of my time but drew a blank on an open trough calc. Simple when you know how!!

Thanks again
icw