“Understanding and mitigating flooding is becoming a critical issue around the globe”, explains Sales and Marketing Director Paul Banfield. “Analysis and prediction of potential flood extent, depth and velocity is a complex problem, particularly in urban areas where drainage networks can reduce flooding in some areas, while increasing it in others.
“One-dimensional (1D) simulation can provide extremely good information about floodplain flows and depths, and is a fast and efficient method for determining maximum extents of flooding but has to rely on assumptions about direction of flow. It is also limited when detailed information about overland flow velocities is required, particularly when flow paths are heavily influenced by the obstructions caused by urban infrastructure and buildings.
“Two-dimensional (2D) simulation is better suited to modeling flows through complex geometries such as urban streets and buildings, road intersections and other transport infrastructure, and open ground where either source or direction of flow is problematic to assume. In urban areas the situation is exacerbated further by the presence of sewer networks, in which flows can both enter and exit the system during flood events. Modeling such complex flow scenarios both accurately and efficiently requires a model with both 1D and 2D engines.”
Wallingford Software’s flood modeling solution combines both one-dimensional and two-dimensional simulation within InfoWorks. InfoWorks 2D provides all the functionality necessary to completely model the interaction of surface and underground systems, including tools usually associated with GIS packages such as the creation of 2D meshes and fully animated flood maps. The integrated 1D and 2D models benefit from the standard InfoWorks functionality including data import, validation, version control, audit trail and display of results. By using 1D simulation to identify where flooding happens, and then using the combined 1D and 2D simulation to investigate the direction and depth of flood flows in these smaller areas, users can achieve a cost-effective balance between model-building time and simulation accuracy.
“Some existing solutions assume that a 2D model of the whole study area has to be built”, says Paul Banfield. “With InfoWorks 2D, smaller detailed 2D models can be created within a single 1D model dramatically reducing the model size - minimizing the time spent building and simulating these models.”
With InfoWorks 2D, modelers have the ability to undertake flood studies in one package, improving their productivity and increasing quality control at a very reasonable cost. Early adopters of the solution will be able to establish themselves as experts within this fast-growing market arena. InfoWorks 2D will be available with InfoWorks CS v8.5, InfoWorks SD v8.5 and InfoWorks RS v9.0.
Wallingford Software’s Director of Product Management, David Fortune, said: “This new solution marks a profound change and radical improvement to the way that flood modeling is approached. With the new 2D capability tightly integrated within the market-leading InfoWorks products, modelers will be able to achieve highly-detailed and accurate simulations of flood events, particularly in areas such as urban landscapes that have previously been challenging to model.”
2D fluid flow engine
2D finite volume methods are used to solve the shallow water flow equations, using the Rienmann solver with a TVD shock capturing model that makes it particularly suitable for rapidly varying flood flows such as those through steep streets and road junctions and those associated with bank overtopping or breaching. The 2D and 1D simulation engines run simultaneously allowing the exchange of water in between the models at each timestep.
For InfoWorks CS and SD, the exchange of water between 1D and 2D takes place at the manholes. Standard model building tools within InfoWorks automate the connection of nominated manholes in the 1D model to the appropriate cells in the 2D model. For InfoWorks RS, the flow exchange will occur at modeled spill elements.
Unlike the majority of commercial modeing solutions, which rely entirely on an underlying quadrilateral grid, the InfoWorks 2D module is based on a surface mesh, giving maximum flexibility to the modeler and ensuring that the system topography is modeled as accurately as possible. This flexibility in the mesh increases the type of flows that can be modeled.
A number of different mesh types can be used and combined in one model, including triangular unstructured mesh which is the solution of choice for analysis of complex flood flows such as those found in urban areas, quadrangular unstructured mesh which is suited to channelled flows, and multiblock rectangular mesh for simpler flow patterns.
One of the keys to the efficiency and ease of use of the 2D engine is the automatic generation of unstructured triangular meshes from within InfoWorks. Meshes generated by third party meshing tools can be imported, but it is not necessary as InfoWorks 2D is a complete solution. The inbuilt mesh generator includes functionality to control the resolution by both maximum triangle area and/or minimum triangle angles. The specification of the mesh can be varied for different areas of the model, allowing high resolution to be maintained around key features while using a lower resolution for flatter, featureless, less important regions.
The mesh generator can also include voids (buildings), break lines and walls to add further definition to the hydraulically important features and use a range of polygons to specify individual roughness zones. This is crucial to accurately simulate flow around buildings, on roadways and across areas of open ground such as parks. The data required to generate the model mesh can be imported from background layers, external files or 1D network features.
The 2D engine produces water levels at the centre of each mesh cell and velocities across each of the cell faces. These results are fully integrated with 1D engine results. The combined results can be viewed as graphs, tables or animated, thematic flood maps. The flood maps can be exported to GIS if required.
InfoWorks 2D supports the use of OpenMI, the European standard that enables simulation models of environmental and socio-economic processes to be linked by exchanging simulation results timestep by timestep. OpenMI is appropriate for use in situations where integration of InfoWorks 2D with pre-existing models is required.