Applies To
	Product(s):	Bentley SewerGEMS, Bentley CivilStorm, Bentley StormCAD
	Version(s):	08.11.03.84+
	Environment:	N/A
	Area:
	Original Author:	Mark Pachlhofer and Jesse Dringoli, Bentley Technical Support Group

Problem

Can StormCAD use the HDS-5 calculations that CulvertMaster uses to compute culvert hydraulics?

Background

Starting with StormCAD version 08.11.03.84 (Select Series 3) and up you can designate the pipe entrance should act as a culvert, by selecting “True” for the “Is culvert?” the conduit properties. Standard HDS-5 culvert coefficients and calculations are used.

The other approach typically used in older versions would be with a catchbasin. Since all the flow that approaches a culvert entrance enter the pipe, you would choose a generic type inlet/catch basin, with 100% capture efficiency. To check your headwater depth, you would use another program such as Culvertmaster. This way, you`ll know if the headwater is acceptable. Without using the "Is Culvert?" option StormCAD does not calculate inlet control at the inlet location: once the flow is inside the subsurface structure, StormCAD will perform the backwater calculations and compute outlet control.

As for the attributes of the generic type inlet, setting the bottom of the culvert as the invert elevation (at the end that is exposed to daylight) and the top/crown of the culvert as the rim elevation is recommended. You can use an approximation for the ground elevation

Solution

If you set the property located under the Physical(Culvert) section of the model to "Is Culvert?" = 'True' you can choose to use the conduit headwall/endwall definition for the culvert, which is provided by specifying the culvert headwall in the culvert inlet coefficients manager and choosing the label for it. See screen shot below:

You can also choose to  define the headwall/endwall using the start/stop node, which should be headwall elements that already has the information found in the Culvert Inlet Coefficients incorporated into it.  

Headwall solution

Starting with the SELECTseries 4 release of StormCAD, you can also use a dedicated headwall/endwall node element (in place of the cross section in the above example) to model the ends of the culvert. Culvert hydraulics are still modeled by way of the HDS-5 coefficients, but the headwall element has added connectivity abilities that allow you to, for example, start a pipe with a headwall element with a catchment directly connected. For more information see this headwalls technote.