Configure the simulation window

This section explains how to prepare a new 2D model simulation. It also describes how you can link a 1D network to your 2D model.

There are an extensive range of model settings and options available for affecting your 2D model. However, many of these can be left on their default settings. Further details on how all 2D model settings will affect your simulations area provided in the technical reference section of the user guide.

The following describes the minimum settings that must be defined to enable a 2D model to be run:

1. Create a new 2D simulation
   Create a new 2D simulation file (xml file) within your project. This can be done by navigating to the Simulation tab and clicking the New 2D Simulation button. Alternatively, right-click the Simulations section of the Project panel and select New 2D Simulation from the menu.
   
   You will be prompted to provide a filename and location for the new 2D model file. The 2D model definition window will then be displayed with General tab initially selected, as shown below. The specified filename is entered here as the default name for your model. This tab also enables you to set the duration of your simulation and specify some general options to alter how your model will run (see General tab section in the 2D simulation details of the user guide)
   
   In addition, the new simulation name will appear in the Simulations section of the Project panel.
   An initial domain is automatically specified (given the name Domain 1, though this can be edited). This represents one computational area of your model. You can define multiple domains, e.g. separate left bank and right bank models, or include multiple active areas in a single domain. These different options will provide different efficiency levels depending on the shape of your active areas.
2. Add general simulation details
   On the General tab you need to specify the run duration for your simulation. This can be set with a simulation length, start and end dates or set to run until the peak flow of your inflow hydrograph.
   
   Note:

   The simulation time step is set on a per domain basis. The value is specified on the Domain Details sub-tab (of the Domain tab)

3. Add simulation domain details
   Add domain details to your simulation by selecting the Domains tab. The Domains tab contains several sub-tabs for entering data for each defined domain. The settings that can be used to define a domain are:
   • Topography – your ground grid file (this is essential) plus the option of specifying any additional shapefiles defined to represent topographic updates. You can use the Add button to browse to a file or simply drag files from your Layers or Project views in the main interface and drop then into the 2D model definition window. If you enter multiple topographic files in a 2D model then Flood Modeller will read this list from top to bottom, with each subsequent layer overwriting the previous one (where overlaps occur). So, a 2D model should be defined with the baseline ground grid at the top of the list and topographic features that overwrite this in subsequent rows.
     
     Note:

     If you enter multiple topographic files in a 2D model then Flood Modeller will read this list from top to bottom, with each subsequent layer overwriting the previous one (where overlaps occur). So, a 2D model should be defined with the baseline ground grid at the top of the list and topographic features that overwrite this in subsequent rows.

   • Computational area – automatically set from the extents of your ground grid, but you can edit these parameters to reduce the model extent. You also have the option of loading these parameters from a shapefile (which can be drawn in Flood Modeller and dragged onto the Load button from the Layers or Project views). It is recommended you at least consider reviewing the grid size to select a value that provides the required balance between run time and model resolution.
     The computational area can be rotated so that computation grid cells are aligned to the primary flow direction, which can lead to an improved model performance.
     Note

     Take care rotating grids as this can lead to problems when calculating flood depth grids from model results (as these must be converted back to an x-y orientation and rounding errors can creep into this conversion).
     
     When using rotated grids, certain approximations are made to translate the input data to grids with rotated square cells. The quality of this translation depends on the discretisation of the domain and may affect simulations of channel flows, especially when the number of cells across channels is low. Therefore, a finer resolution (i.e. a smaller cell size) will reduce such effects.
   • Active area – If specified drag your active area shapefile from the Layers panel (or Project panel) onto the provided space in the 2D model definition window (alternatively a browse button is also provided for adding an active area).
   • Surface roughness (Manning’s n) can also be set on the Grid Data sub-tab. A default global value is provided. You can edit this value and/or drag/import one or multiple shapefiles or raster grids to define areas of different roughness within your model extent, e.g. UK Mastermap shapefile data (requires associated .fric text file to cross reference land use types with roughness values). For any model area outside that defined by additional roughness files the global default value will be applied.
     
   • The type of 2D simulation to be used can be set on the Options sub-tab or by double-clicking on a domain in the Domains table.
     
     The Options sub-tab also allows you to adjust the associated calculation engine parameters for each domain. However, in most cases, these can be left on their default values (refer to the 2D model technical reference for definitions of all settings available).
     Note:

     A 2D FAST model uses simulation length setting in a different way to the other solvers. Refer to the Technical Reference section Pre-processing for further information on setting up a duration for a 2D FAST simulation.

   • Boundary inputs to your 2D model can be set either on the Boundary Conditions sub-tab or by setting up a link to a 1D model.
     On the Boundary Conditions sub-tab a table is provided for you to add boundary inputs. New boundaries are defined using the Add button. This displays a new window in which you are required to specify the following:
     • A shapefile drawn within your model extent, usually a polyline, defining the location of the inputs.
     • The input parameter, e.g. flow, is selected from a dropdown list of options.
     • The input data format associated to your boundary. This can be a single fixed value, a time series (in a separate csv text file or typed into the table provided in the interface as shown below) or a 1D hydrological event file (ied text file).
     
     
     Alternatively, a link to a 1D model is defined within the Linked Models tab of the 2D model definition window. You can drag your 1D model file and link line shapefile from your Layers or Project views into the spaces provided, as shown below (browse buttons are also provided to select these data files).
     
   • The model outputs that will be produced by default from your 2D model are flow and velocity vector time series and waterlevel and depth time series grids. These will be in a combination of sup/2dm/dat file formats in which the sup file contain metadata (summary of variables output), the 2dm file contains the model grid and the dat files contain the time series values (one file per variable). In addition to these data, the maximum extent timesteps from each parameter, i.e. timestep 9999 (plus 9999.1 and 9999.2 for some parameters), will be converted to separate ASCII raster grids.
     The Outputs sub-tab (on the Domain tab) enables you to customise outputs for each domain within your model. You can select different grid and vector output parameters, with different output formats (grids or point time series). Available formats are:
     • Time series grids - 2dm/dat SMS or XMDF format
     • Maximum extent grids – ASCII raster or GeoTIFF grid format
     • Point time series – CSV format
     You can also specify additional custom outputs for a simulation. These can be mass balance files (text format), check files (raster grids, .asc), flood hazard outputs and flow totals crossing a specified line. It should be noted that Flood Modeller post-processing tools can also generate flood hazard and flow totals crossing a line data from your standard flow, velocity and depth outputs.
     
4. Settings on the Options sub-tab in most scenarios should be left on their default values. Refer to Options tab for definitions of all settings available.
5. Click the Save button at regular intervals and at the end of specifying your model to store your model settings. If your 2D model is not fully specified, i.e. producing a valid 2D xml model file, then you should see a warning message detailing the required settings that are missing.
6. After you close the 2D simulation window you can return to make further edits by double-clicking on the appropriate filename in the Simulation section of the Project panel (or right-click on the filename and select Open from the displayed menu).
   Note:

   The 2D model simulation file generated by Flood Modeller is an xml format file. This can therefore also be accessed using suitable text editing software. You can then review the file structure and make additional edits if required. However, this is not recommended and any changes should be performed with care. You can refer to the XML format pages within Technical References Section of the user guide for details on the structure and format of the 2D xml simulation file.

You are now ready to Run the simulation and review the outputs.