Does Autodesk Drainage Analysis support inlets with bypass links?

[qchalmersKACEH]

I am testing the new Drainage Analysis tool for C3D 2026 to see if it can provide the same capabilities as Autodesk Storm & Sanitary Analysis. Our current workflow requires the calculation of gutter flow spread to meet the requirements of Table 5-1 of the WSDOT Hydraulics Manual. In Civil3D there are structure properties for inlets but I am unable to figure out how to create a bypass link between structures. The help pages on Drainage Analysis do not include any mentions of inlets or bypass links. Am I looking for a feature that doesn't exist?

I've also looked into Autodesk Hydraflow but it doesn't appear to support bypass links either.

With the official announcement that SSA has been discontinued what software are we supposed to use for flow spread calculations?

[matt_anderson_pe]

Analyze Gravity Networks should work.

[qchalmersKACEH]

Are you saying Analyze Gravity Networks can use bypass links to route flow that does not enter an inlet to the next inlet? How do I add a bypass link?

[matt_anderson_pe]

There isn't a routing - but any flow bypassing an inlet gets passed to next inlet by specifying the target.

Bypass Target

Specifies whether excess flow from the line goes to another line (such as the next structure in the pipe network) or offsite. You can click in the field to display a drop-down list with choices to specify the structure to which the flow is sent to, or you can specify Offsite if the flow is sent to another pipe network or location.

[qchalmersKACEH]

How does the flow to a bypass target enter that structure? Is it evaluated against the inlet properties of that structure or the whole bypass flow just injected directly into the structure?

It appears from another forum thread that these bypass targets are not correctly saved when exporting the model and the bug has never been fixed by autodesk:

https://forums.autodesk.com/t5/civil-3d-forum/hydraflow-storm-sewers-forgets-bypass-targets/td-p/102...

[matt_anderson_pe]

Bypass target simply pushes water to that inlet.

Hydraflow and Analyze Gravity aren't linked so a bug in Hydraflow Storm Sewers wouldn't be linked with AGN.  

[qchalmersKACEH]

Jesus how many different Hydraulic Analysis tools does Autodesk have? So far the ones I have heard of are SSA, Drainage Analysis, Analyze Gravity Networks, Hydroflow and Infodrainage.

This answers my question however, we are looking for software that integrates with C3D and can correctly calculate bypass flows from multiple inlets in sequence. Sounds like Drainage Analysis will not.

[Charlie.Ogden]

The Technical Preview of Drainage Analysis for Civil 3D does not yet direct the bypass flow to the target inlet. However, it is listed on the Civil Infrastructure Public Roadmap here. 

The Analyze Gravity Network command that Matt mentioned is a tool integrated within Civil 3D that currently does what you are asking for. It uses the Rational Method for flows and the inlet calculations from HEC-22. The bypass flow is added to other flows reaching the bypass target inlet, but the inlet properties are still used to determine what that inlet can capture. 

The tools like Hydraflow and SSA are separate stand alone applications acquired by Autodesk. Analyze Gravity Network and Drainage Analysis are tools built by Autodesk to better integrate the functionality right inside of Civil 3D.  The latter leverages the same calculation services that can be accessed by InfoDrainage.

[qchalmersKACEH]

Hi Charlie, thank you for the response, this is very helpful. My company has been using SSA for inlet bypass and lane flow spread calculations and were disappointed to hear Autodesk has discontinued the program. We are currently experiencing this bug with SSA and are in a panic to find a different program as Drainage Analysis doesn't support bypass yet (as you mentioned) and Analyze Gravity Network doesn't support SBUH. I have a 1,300 home residential project and the jurisdiction recommends SBUH over rational method so that is what we have been using for the first 3 of 10 phases (and intend to continue using).

If you know of a software that Autodesk supports with these capabilities please let us know.

[Charlie.Ogden]

In SSA on the Profile Plot, can you use "Copy Profile Plot..." and past the image into Word or something similar, then print from there?  I have not upgraded to Windows 11 on this machine yet to try it myself, so I will check with our QA to see, but I suspect the bug has more to do with print spooling than copying anyway. The team was looking at the bug, but hopefully copy and paste helps you in the meantime.

[qchalmersKACEH]

Hi Charlie,

We just tested this and it does work. We will be using this workaround for now while we are waiting on Autodesk to confirm a long term fix. I have already filed a support ticket through my company's Autodesk provider (Topcon) and they have reached out to Autodesk on my behalf for a timeline on a permanent fix.

[qchalmersKACEH]

I received confirmation that Autodesk will not be patching this SSA bug and my company is required to switch to a different software solution. SSA has been included in our Autodesk product package at no additional cost for years. The only product Autodesk currently offers with inlet bypass analysis is Infodrainage which is fairly expensive. For this reason my company will likely switch to a different software, Geostorm.

@Charlie.Ogdenif Autodesk had inlet bypass analysis in their new 2026 Drainage Analysis tool we would be happy to try it. What is the timeline on this feature being implemented?

[matt_anderson_pe]

Technically, InfoWorks ICM can perform the same gutter spread calculations, is easy to set up, and is much more expensive than InfoDrainage.  [Just dont use the SWMM engine in ICM - no inlets]

Other third-party tools based on SWMM include EPA-SWMM.  GeoStorm uses SWMM, PCSWMM uses SWMM, TUFLOW uses SWMM.  Each has benefits and from what I recall - PC and TUFLOW are cheaper than InfoDrainage.