Perforated Riser in Hydraflow Hydrographs

[salbright38QJG]

This is my first time trying to design an existing perforated riser in Hydraflow. The input allows for the number of holes and the invert, but how do you account for multiple rows of holes? There's not a place for the vertical spacing is there? 

[matt_anderson_pe]

@salbright38QJG 

You answered your own question. Help shows:

Culvert D is reserved for a perforated riser and is treated differently from other culvert/orifice devices. Perforated risers consist of a riser pipe with several holes of the same size and at a uniform distance (S) apart. These structures are typically used in a multi-stage configuration with culvert A as the outlet pipe and in conjunction with a riser weir. The inputs for perforated risers are the same as for culvert/orifice structures, except Length, Slope and n-value are substituted for Height.

In this case, your Invert, Rise/Span and Height will define the uniform spacing of the riser.

Matthew Anderson, PE 

[salbright38QJG]

@matt_anderson_pe , If I'm only putting in the number of holes and overall height, how does it know how many per row? I'm not putting in the spacing between holes anywhere. Also, is the number of holes input intended to be the total number, or number per row? Either way it seems like it's missing a spacing component to it. The diagram shows an 'S' dimension for the distance between center of two adjacent holes, but there's not a spot for the on the Outlets input tab.

[fcernst]

It's kind of a confusing implementation.. to understand you have to go back and look at the approximation (McEnroe 1988) it uses..

It only uses the entire available cross-sectional area of all the holes...

[matt_anderson_pe]

That's correct - it's not performing 72 individual orifice calculations.