how to define pipe crossing

Hello Ammar,

We may need more information on the setup of this. One thing to consider is using a conduit control structure, if the crossing pipe partially blocks flow in the conduit. If that isn't what you are looking, we will need additional information on this.

Regards,

Scott

Thanks Scott,

Actually, the pipe is crossing from the midway(center) of the culvert as shown in the cross-section attached to my last question. if it would cross from the bottom I could use "weir" as a conduit control structure. what can I do in this scenario since it has a clearance of waterway from top and bottom of crossing pipe? please elaborate further.

Thanks, Yashodhan for your reply.

let me brief you about the existing & proposed situation.

Existing Situation:

In the existing situation, a tributary is falling into the main drain as shown below. There are no restrictions

Proposed Situation:

In this case, the sewer is crossing from the tributary. To accommodate the reduction in the crossectional area of a tributary (due to sewer crossing), we have enhanced the width of a tributary. refer attached image.

The likelihood of submergence of sewer pipe during rainfall event is there . we would like to analyze the impact of crossing sewer on hydraulic behavior.

kindly, provide guidance on how to model this scenario in sewergem.

This seems similar to what I have shown in SewerGEMS. The conduit is simply passing through the culvert but is not influencing the hydraulics of the culvert. The only impact that could be is during larger return periods there could be high flows which could lead to conduit submergence leading to infiltration during those events. 

You can calculate the HGL in the culvert during your higher return events and compare it with the invert location of the conduit to know how much of the conduit is going to be submerged. You can input infiltration rate along the length or surface area of the submerged conduit to account for infiltration flow due to submergence.

However, typically there is space above the culvert for road laying / supporting the bridge deck within which the utilities such as storm drains, sewers, power lines etc. are accommodated. These are hydraulically separate and can be modeled as I have shown above.

Is there not enough thickness available between the deck and the pavement top? Can you divert the sewer where there is enough depth available?

Thanks 

Yahsodhan, this proposal has been made after taking all the necessary consideration. the only solution is to cross the conduit within the culvert.

The above image portrays the same condition I want to analyze. "obstruction(conduit crossing) in between the waterway of a tributary".

what sort of impact this conduit crossing shall create upstream of the tributary.

kindly, let me know is there any possibility of analyzing this kind of crossing. 

If you are concerned with a reduction in culvert capacity due to the pipe crossing through it, you could use a start or stop control structure in the conduit element that represents the culvert, as previously suggested by Scott. To model both the orifice (under the crossing pipe) and weir (over the crossing pipe), you could use the Composite Outlet Structure dialog to set up an outlet with both, compute the rating curve, then copy and paste the rating table from the Data tab, to a "user defined" conduit control structure type.

Before doing this though, you could perform a quick sensitivity analysis, reducing the pipe diameter by a large amount to see the impact it has on the system. If a significant impact is not seen even with a large reduction, then this may tell you that you do not need to worry about the impact of the crossing pipe or have to try to model it with a conduit control structure.

It works. Thanks Jesse for suggestion. 

It works. Thanks Jesse for suggestion.