2D Simulations - Boundary Conditions Sub-tab

A 2D Solver model requires input data to apply water into (or out of) the modelled region. This may be one or more of the following: link from a 1D model; hydrology/rainfall source or flow/elevation data at an external or internal boundary. The following parameters can all be defined as boundary data:

Hydrological inputs (e.g. rainfall) are covered in the next section.

The Flood Modeller 2D Solver allows the user to locate boundary datasets within your model by associating data to a shapefile feature, which can be a point, line or polygon. In this case if you are associating shapefile features to Flood Modeller node names in a separate text file (see below for details), then your shapefile must have an attribute field entitled ‘node’ containing the cross referencing to the node names in your text file. At runtime different data types associated to a feature will be treated differently:

Different options are also provided to define the actual data assigned to each boundary:

The 1D Solver hydrological boundary will contain hydrological parameters rather than time series data. When you start your simulation 2D Solver will use these parameters to calculate a time series input to be applied over the areas of your model defined by the associated shape file.

Setting Boundary Inputs in the 2D Simulation window

For each domain in your model you can specify one or more flow, depth or water level boundaries. These data can be specified as single values or as time series. They are located within your domain by associating your boundary data to a shapefile feature. This section details how these data are specified within the 2D Simulation window.

All boundary data are specified on the Boundary Conditions tab (a sub -tab within the Domains tab). When first accessed this looks like the example below, displaying one blank table:

Defining a new boundary input

To add a new boundary to your model, click the Add button on the Boundary Conditions tab. A window will open. This window is shown below:


This window provides a series of options to define your new boundary input:

  1. Boundary condition – here  you can select your boundary parameter. It is selected from a dropdown list of variations of flow and water depth (or level) available for inputs:

    Boundary conditions data types are all variations of flow, water depth or water level. The data types that can be utilised as 2D Solver boundary inputs are summarised as follows:
      • Water elevation – water level data, elevations above a datum specified in metres or feet (depending on your system setup, i.e. SI or US units).
      • Inflow – flows to represent sources coming from underground, e.g. sewer overflows (at manholes) or overflows from flooded underground structures (tunnels, basements, etc). These types of flow inputs will be treated slightly differently in the 2D Solver calculation engine and so may yield different results. Units are the same as total flow.
      • Inflow per unit width – vertical flow converted into a per unit width value. 2D Solver will multiply values by the width of your boundary to determine actual flows entering each cell of your model domain
      • Elevation – water level data the same as water elevation boundary type. It is the modeller’s discretion which of these options is used as the choice will not affect model results.
      • Depth – water level data converted to actual depth (by subtraction of underlying ground level). Values must be specified in metres or feet.
      • Normal Depth – calculates the normal depth-flow relationship at a boundary and is usually used as an outflow boundary. The location can be specified by a shapefile (point or polyline) and user-defined slope, or if a shapefile is not specified, it may apply anywhere around the domain boundary. The latter (free location) case is useful when the outflow location is not known a priori, but results should be interpreted with care if there exist multiple outflow locations since the relationship is calculated for the entire domain boundary; in the free location case, the slope is not entered, but calculated as the water surface slope. In either case, the boundary is only activated when water reaches the boundary and the relationship is only calculated using those boundary cells, which are wet.
  2. Boundary location – Here you need to specify a boundary shapefile, either by typing a filename (with full path) into the space provided or by using the adjacent button to browse to your shapefile.

  3. Boundary data – the default setting assumes that your boundary input will be constant flow in cumecs. If this is the case you can type a single constant value for your boundary input. This value will then be applied continuously throughout your subsequent simulation.  

    The other options for assigning data to your boundary are as per the radio buttons on the "Add/Edit Boundary Condition" form shown earlier: :

When a boundary is defined with a boundary data option set to ‘User entered time series’ then the time series table will be enabled on the Add/Edit Boundary Condition form. To enter a value in here, simply click a cell and type in your coordinate value. Then press the Enter or Tab key to commit a value. When an X and Y coordinate pair are completed in the table, a new blank row will automatically be created ready for your next entry.

This table also provides a menu accessed by right-clicking on the table.

This provides the following functions:

  • When a boundary is defined with a boundary data option set to ‘User entered time series’ or 'Time series file (csv/ied)'  then a menu "Units of time are:" is enabled for your data series. This is set by selecting from the provided options in a drop down list located above the chart (this chart is not greyed out only when the time series table is also enabled).
    1. When your new boundary settings are defined click the OK button (or click Cancel to discard the boundary). The new boundary will be added to the Domain boundaries table on the Boundary Conditions Tab in the 2D Simulation window.

      When the new boundary is highlighted in the boundaries table, it is possible to edit this boundary by either double-clicking on the line or clicking on the Edit/View button at the bottom of the screen. Then you can modify the boundary by editing the values on the Add/Edit Boundary Condition form and clicking OK and subsequently confirming that you would like to Save the changes on the window that opens.


    Domains Tab Introduction

    2D Simulations Introduction