Integrating SewerGEMS or CivilStorm with OpenFlows Flood for 2D simulations

Product(s): OpenFlows FLOOD, SewerGEMS, CivilStorm
Version(s): (for OpenFlows FLOOD); CONNECT Edition, V8i (for SewerGEMS & CivilStorm)
Area: Modeling

This article is an introduction to OpenFlows FLOOD’s integration with SewerGEMS and CivilStorm, for 2D simulations of surface overflows from 1D hydraulic models.


OpenFlows FLOOD is the latest product offering by Bentley Systems which integrates a coupled version of the MOHID Land and EPA-SWMM solver. This enables you to dynamically simulate the interaction between the storm water drainage system and the surface runoff. OpenFlows FLOOD is a GIS-based platform to analyze and simulate flooding in urban, riverine and coastal environments.

MOHID Land is a numerical engine composed of four compartments or mediums (atmosphere, porous media, soil surface and river network) and water moves through the mediums based on mass and momentum conservation equations. MOHID Land can be used to simulate flood events along with the simulation of erosion and biogeochemical processes necessary to simulate suspended sediment and nutrient loads evolution.

OpenFlows FLOOD also enables the comprehensive simulation of coastal flooding through the inclusion of the MOHID Water engine, enabling the realistic estimation of sea level rise as a result of storm surges or tsunamis.

MOHID Water is a three-dimensional numerical engine used to simulate surface water bodies (oceans, estuaries, reservoirs), and has been applied to several coastal and estuarine areas demonstrating its ability to simulate complex features of the flows.


The release of OpenFlows FLOOD with the inclusion of a 2D model for surface flow has some of the following benefits when compared with a 1D approach:

• Fewer modeling assumptions and less user judgment yield results that are more representative of actual conditions.

• Enhanced communication with stakeholders with engaging graphics, videos of flow paths, and georeferenced results.

• Accurate representation for complex conditions, including wide floodplains, sinuous channels, multiple channels, bends and confluences, bridge/roadway crossings, roadway overtopping, skewed roadway, tidal waterways, and bridge scour, among other conditions.

In addition to these aspects, Bentley Systems also integrated in OpenFlows FLOOD a numerical engine for coastal circulation (MOHID Water), which allows to estimate coastal floods, including storm surges and tsunamis.

Finally, with full integration between OpenFlows FLOOD, SewerGEMS / CivilStorm, ContextCapture and LumenRT, we can visualize urban flood results in an immersive and visually striking 3D reality modeling interface.

Modeling Environment

OpenFlows FLOOD modeling environment consists of three fundamental aspects:

• The 2D domain which is a horizontal grid that defines the surface. This grid can have a fixed or a variable spatial step.

• The 3D domain which defines the porous media. This is essentially the same 2D horizontal grid of the surface with a vertical grid to accommodate variable layer thickness.

• The 1D domain which defines the river reaches / storm-sewer network which connects to the surface.

Network modeling, analysis and simulation in SewerGEMS or CivilStorm falls within the 1D domain.

The solution in OpenFlows FLOOD would integrate the 1D (piped network) modeling in SewerGEMS or CivilStorm with the 1D (river reaches) and 2D (surface) domains of OpenFlows FLOOD and optionally, a 3D module to simulate the flow in saturated and non-saturated soil (infiltration and exfiltration). The models are linked dynamically allowing to compute and simulate overland flows due to flooding of piped systems, convert rainfall to surface overflow, flooding analysis and integrated catchment modeling.

Sea levels can also be simulated in OpenFlows FLOOD (using MOHID Water engine), to be used as downstream boundary conditions to the integrated modeling approach followed above.

Model Setup

Before bringing in the SewerGEMS or CivilStorm model the OpenFlows FLOOD environment must be setup. To develop a model in OpenFlows FLOOD the following files will be required (at a minimum)

• A digital elevation model (DEM) of the project area (e.g. GDAL Raster formats such as ARC, ADF; ESRI shapefiles; automatic importing of NASA DTM worldwide database; or XYZ file in native format)

• The stormwater network prepared in SewerGEMS or CivilStorm (Explicit – EPA SWMM Solver).

The DEM loaded in OpenFlows FLOOD (and using Bing maps as a background layer) would look like this:

OpenFlows FLOOD requires a computational grid to calculate the overland flows. All the data processing / preparation and analysis is done based on this.

Based on the DEM and the selected grid mesh, a gridded Digital Terrain Model (DTM) needs to be generated to use as a surface which shall be used in runoff calculations. Along with the topography you must specify the surface properties (roughness) which will be used in computing the overland flow.

The linking of a SewerGEMS or CivilStorm model connects the 1D model with the 2D environment of OpenFlows FLOOD. To simulate overland flow, OpenFlows FLOOD will run an integrated 1D / 2D model which requires the stormwater model file (.inp) from SewerGEMS / CivilStorm. This can be obtained by exporting the SewerGEMS / CivilStorm model to SWMM v5 (File > Export > SWMM v5).

The .inp file can then be imported into OpenFlows FLOOD to connect it to the 2D environment. In OpenFlows FLOOD we can select “Connect Stormwater model to MOHID” under the “Urban Floods” Toolbox;

Selecting this option opens a dialog box in which you have to specify the DTM (surface) where this stormwater network must be loaded, the path of the .inp file and the projection of the system.

The added storm-water network would look like this on the map:

The overland flow or flooding at manholes is dynamically calculated at each time-step giving us 2D maps which show the extent of flooding.

See Also

2D Modeling of Urban Flooding

Bentley Press Release

Coming Soon

Quick Start Guide for Integrated Urban Flood Simulation using OpenFlows FLOOD + SewerGEMS / CivilStorm.

Walkthrough Guide for the implementation of a model application on a surface flow from a surcharging sewer in an urban area.

Tech Talk / Webinar on OpenFlows FLOOD: Integrated Flood modeling for understanding and mitigating flood risks in urban, riverine and coastal systems.

OpenFlows FLOOD Capabilities Video

Context Capture + OpenFlows FLOOD + LumenRT Solution