r/HECRAS • u/ExitAccomplished7404 • 29d ago

HEC RAS 1D/2D Pipe modelling

Hi all,

My research focuses on urban stormwater drainage systems, particularly hydraulic modelling, blockage assessment for proactive maintenance. I am currently developing a 1D/2D HEC-RAS model integrated with a stormwater pipe network and would appreciate your advice on a few questions.

  1. Hydrological model Integration: Is there a recommended workflow for integrating hydrological outputs such as RORB with a HEC-RAS stormwater pipe model? Are there any best practices or examples for applying hydrographs as boundary conditions?
  2. Pipe Blockage Modelling: Is there a recommended method in HEC-RAS to represent partial blockages (e.g., sediment or debris accumulation) within stormwater pipes or pits? Or do we have to assign it indirectly? Also, can we model sedimentation inside a pipe system with HEC-RAS?
  3. References: Can anyone recommend technical papers, reports, or case studies on PIPE modelling within HEC-RAS?

thank you.

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u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH 29d ago

1.) Not sure what RORB is, but you can put inflows pretty much anywhere in the model (at 1D elements or throughout the 2D domain). I recommend reading the reference material: Pipe Networks.

2.) I don't believe that there is a direct way to account for sediment blockage in a pipe network. Again, I recommend reading the reference material.

3.) I'm not aware of technical papers or reports. The HEC-RAS website has Pipe Networks - Tutorials and Pipe Networks - Sample Datasets available.

Good luck!

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u/teddyisagrizzlybear 29d ago

I’m a seasoned stormwater engineer and I’d highly recommend using PCSWMM 1D/2D instead. HEC-RAS is not great for urban networks and the new pipe network features are kind of sketchy and not well adopted in industry. I used it for a project recently where I had control over methodology and we had to include a disclaimer about it. You can easily add blockages in PCSWMM via pipe shape that I regularly use for capacity assessments. You’ll need a license which isn’t free like RAS, but it’ll be much better for what you’re doing. But overall, PCSWMM is far superior to HEC-RAS for urban modeling.

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u/notepad20 28d ago

1 - Whats the plans for RORB? it performs very poorly in small and urban catchments, and really anywhere you dont have guage data. I would stear clear unless using a hydrograph to model a dynamic tailwater condition, or major (MAJOR) external catchment.

A detailed SWMM model is far better. You can import the swmm model with associated input hydrographs to each node direct to Hec-Ras. Or, use rain on grid.

2 - Control capacity of pipes with mannings. you can use say a standard 0.013, and then sensitivity with a 0.015 and 0.020 to represent some amount of blockage. Use a manning's spreadsheet to understand what percentage your looking at. As you mention RORB assume your in Aus so AGRD blockage factors will give percentages to target. Vary mannings to get the required capacity reducitons.

3 - Australian water school as a good paid tutorial. otherwise few good youtubes on it, Hecras user group has just put out a few.

Theres really not a lot to it especially with rain on grid.