How to use the 1D Flood Calculator

Basic Operation

The functionality “1D Flood Calculator” allows you to generate a grid or shapefile to represent a flood extent from a 1D model. The required input data are a raster grid of ground levels and a water levels dataset. The latter can be a TIN with associated 1D model results or it can be a simple Static Flood Extent from Grid that represents a flood level. The flood extent is calculated by determining the difference in elevation between the ground and water data sources.

You can select to output their flood extent data to a raster grid format or a shapefile format. Raster grid options are binary .flt grid or ASCII .asc grid. The shapefile output option generates polygons that outline the calculated flood extent, i.e. separate polygons around each 'cluster' of wet grid squares. It should be noted that with this latter option no depth information from the source data is retained in the output file.

The Flood Calculator window can be accessed by Selecting 1D Flood Map icon from the Results tab.

To use the tool you should already have your desired input data, i.e. ground grid and water level data (on a TIN file), loaded in the viewport of Flood Modeller.

The interface offers the following types of flood map calculation:

  1. Calculation of a Flood Extent from TIN. This option creates a map of the flood extents based on the results from 1D model;
  2. Calculation of a multi-time step grid output (2dm/dat format as produced by 2D models also). This option produces a file that can be viewed as an animation that shows the build-up and then recession of flood water during a simulation.
  3. Calculation of a Static Flood Extent from Grid. Using this option, it is possible to create a flood extent map without using the TIN. The user has to specify the water level for which the static flood extent is to be calculated;
  4. Calculation of a grid of water levels. This option creates a grid of water levels without using any ground grid (this is a variation of option 1).

You specify the required calculation using the radio buttons on top of the 1D Flood Calculator window (shown in above figure). Depending on the type of the flood map calculations, certain options on the window will be enabled or disabled. More details about each type of flood map calculation and the options available are provided below.

1D Flood Calculator Controls

Within Flood Calculator a number of options exist allowing you to tailor the flood map calculation to your specific needs. These options are:

Calculations can take time if large datasets are selected. The calculation progress is shown on the status bar below the viewport of the main interface. Flood Calculator runs separately from Flood Modeller thus other functions can be accessed while the depth grid(s) are being generated.

Batching Multiple Calculations

If multiple flood extents from different time steps, different results sets or different ground grids are required then calculations can be grouped into a single batch run.

To define a batch run, after specifying the parameters for one task of flood calculations and clicking on the Add button, simply define the parameters for the second task and click the Add button again. More information about the input data for the task is mentioned below. The list of individual tasks to be performed in the batch runs is stored in the table on the right-hand side of the screen (the batch run table).

After all desired tasks have been defined click the Run button to start the batch run. A progress bar and status messages are displayed below the viewport in Flood Modeller to inform you of progress through the series of requested calculations.

The tasks list can be saved to enable it to be reloaded and reused later. After defining all required tasks click on the Save button (located at the bottom of the 1D Flood Calculator window). You are prompted to specify a filename for the batch data, which will then be saved with extension .cbt. The Load button can then be used later to reload the list of defined tasks back into the batch table.

Working with a Static Flood Extent from Grid

The simplest form of a flood extent is generated by overlaying a fixed water level across the entire ground grid. Areas where the ground is below this water level will then show up wet. The 1D Flood Calculator provides the option to introduce a Static Flood Extent to represent a fixed water level instead of using a combination of a TIN and 1D model results. The selected ground grid data will then be subtracted from this plane to yield a flood extent.

The advantage of this method is that it enables a basic flood extent to be created quickly, without performing any modelling. However, the results produced should only be used as a crude initial assessment for the following reasons:

To access the horizontal plane feature in Flood Calculator click on the 'Static Flood Extent from Grid' option located above the list of tasks. The list of available model time step results (in the lower left corner of the window) is replaced by an input box for you to set a horizontal plane water level. When the Input Water Level box appears, it already contains a value which is an average value between the highest and the lowest values in the ground grid highlighted in the Select Ground Grid box. You can overwrite the value by clicking on the Input Water Level box and typing a new value.

After selecting the ‘Static Flood Extent From Grid’ option and specifying an Input Water Level, you can then either add to the task list by pressing the Add button or run the flood calculation immediately by clicking the Run button. In either case you will be prompted to select an output format, output filename and location. By using the Add button and adding the task into the list of tasks, it is also possible to include Static Flood Extent from Grid calculations in a batch run.