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OpenFlows FLOOD v.s.HEC-RAS


From 2D/1D simulations for Wadi and surface water modeling (including road embankments, culverts...etc), how does the two compare in terms of capabilities and features? We do have HEC-RAS but not the other (yet)?


  • From a 1D/2D water cycle perspective, I can synthetize how the processes are modeled:

    You can use OpenFlows FLOOD as a single tool to implement an integrated modeling solution capable of imposing spatially and temporally varying rainfall (using direct rain-on-grid). We can impose the rainfall from a constant value, from one or more timeseries (hydrographs) or from a meteorological model. Once the rainfall hits the surface, rainfall water is converted in 2D overland flow (based in topography), and FLOOD can estimate losses by infiltration and evapotranspiration (both variable in space and time). The infiltration / flow through porous media (saturated and unsaturated) to the ground can also be modeled (in 3D) with variable layer thickness. There is also interaction with the (1D) drainage network through rivers and canals.

    Water moves through all the mediums (atmosphere, porous media, soil surface, and river network) based on mass and momentum conservation equations.  The interactions between the different processes (like water exchange between aquifer and river) are calculated dynamically by the model, using the hydraulic gradients. MOHID Land can model the whole system described above, however the 1D surface drainage network can also be modeled using SewerGEMS (SWMM engine), with the advantage of this solver including a wide panoply of hydraulic structures (including culverts, etc.), among other features and capabilities.

    If stormwater drainage network exist, OpenFlows FLOOD can also integrate this subsurface network, dynamically interacting with both 2D surface runoff and (1D) surface drainage network system. Bidirectional interaction between surface runoff and stormwater drainage network is done through manholes or inlets / storm drains.

    FLOOD can also be used for modeling coastal flooding, including storm surges and tsunamis.

    Finally, on top of all this, FLOOD can be used for modeling water quality (nutrient cycles) and water contamination (microbiology or other contaminants) and sediments transport.

    Now, compiling some of the main differences that we believe you can find in terms of features comparing to HEC-RAS, I would enumerate the following:

    • You can check online all equations and numerical methods, source code, etc. from the 2D flood model (MOHID), because this is a collaborative, free, opensource model. HEC-RAS is free, but not open-source – which means that an advanced user is not able to check source code, or to modify it. It’s a black box.
    • FLOOD 2D model solver (MOHID) was analyzed for an intercomparison / benchmark study from UK Environment Agency. This methodology has been assumed as the major world reference in terms of benchmarking 2D flood modelling. Our results were good. I’m not aware of HEC-RAS 2D performance and benchmarking. Probably those results exist, but I’m not aware.
    • FLOOD can be used as a single tool for integrated2D flood model, while HEC-RAS doesn’t have direct rain-on-grid, infiltration or evapotranspiration (you would need an additional tool called HEC-HMS for other hydrological parameters and processes).
    • GIS: OpenFlows FLOOD is a full GIS-enabled GUI. You can handle GIS data inside (e.g. Bing Maps; shapefiles, RASTER files, etc.), including results visualization. HEC-RAS visualization needs to be handled in separate tools, including RAS Mapper (although is connected to HEC-RAS), which is not fully GIS-enabled.
    • Direct 4D visualization of OpenFlows FLOOD output results in Bentley’s LumenRT, integrating life-like digital nature into simulated infrastructure designs, and create high-impact visuals for stakeholders;
    • Integration with Bentley’s OpenCities Planner, a cloud-based service that enables visualization of 2D, 3D, and GIS data in a city-scale digital twin where you can design, visualize, and communicate projects from large-scale city developments to detailed architectural design;
    • Complete solution for flood modelling (urban, river, coastal) (as far as I know HEC-RAS doesn’t reproduce coastal flooding, and I think you’re not capable of simulate urban flooding because HEC-RAS doesn’t have stormwater drainage modeling capability;
    • OpenFlows FLOOD model applications can be easily ingested by Action Server for implementing a flood forecasting / early warning system. HEC-RAS also have HEC-RTS (Real Time Simulation), but I don’t know I this migration is done, and in the website they mention that they are “unable to provide phone or email technical support to non-USACE customers”.

      I hope I had helped.

    Answer Verified By: A  

  • Hello,

    The responses to this thread and additional information are now documented in the following wiki article;

    Difference between OpenFlows FLOOD and HEC-RAS

    Hope this helps.


    Yashodhan Joshi

    Bentley Technical Support