How to calculate Annual average damages

The Damage Calculator tool can interpolate damages from multiple simulation results to determine an annual average damage (AAD) figure (for each property and an overall total).

See the section entitled How to calculate property damages from a flood depth grid for details on the general operation of the Damage Calculator tool. This section describes only the additional procedures required to incorporate annual average damage (AAD) outputs into your analysis.

1. To calculate AAD you will need to have flood depth grids (in ASCII format – with extension “.asc”) calculated from multiple simulations each representing a different return period / AEP flood event for your model extent. If you have these loaded in your Flood Modeller project they can be automatically loaded into the Damage Calculator tool when you access it from the Flood Modeller toolbox (Post-processing tools section). In addition, you can also specify a property data file to be pre-loaded if it is in point shapefile format and you have it loaded in your Flood Modeller project.

   

2. The Damage Calculator tool looks at each grid filename and attempts to evaluate the associated return period / AEP for each depth grid. These values are used to calculate the AAD values so it is recommended you check the RP or AEP columns in the Events table and amend values that the tool has got wrong.

3. The specification of your damage analysis is done in the same way as described in 'How to calculate property damages from a flood depth grid '.

4. After specifying the analysis, it can then be run. Note that the simulation will take a little longer to complete as you have multiple grids specified. You will see the progress bar pop-up window work through reading each specified grid concurrently.

   The results tables obtained from this analysis will contain additional columns compared to a basic single grid run as the depths and associated damages incurred due to each specified flood extent will be listed in separate columns. Furthermore, the results with AAD ticked on will include an additional column that displays the AAD values for each property identified within the flood extent. In addition, the total ADD for the analysis will be provided at the foot of the results table, under the AAD column. Note the results are grouped such that all flood depth columns are together, then all flood damage columns followed by all AAD columns.

   

5. AAD values will also be exported to the summary csv files and if you export to a new point shapefile, automatically loaded into the Flood Modeller map view.

6. After loading the damage data shapefile in Flood Modeller you can modify the settings to highlight the largest AAD values. This enables you to check for any anomalies at these key locations and thus verify your model results.

   The standard display when a point shapefile is loaded into the map view is shown below. Each feature (point) in the shapefile is displayed with the same size and colour.

   

   Right-click on the shapefile in the Layers panel to display the layer properties (in a new window). Select the Symbology tab and Visual Style sub-tab as shown below:

   

   The display in the map view will now clearly show the locations of properties with maximum AAD values. Use the map tools (i.e. zoom, pan and info tool) to investigate the causes of these high values further.