How to apply property level protection thresholds to my damage calculations

The Damage Calculator tool calculates damages per property for one or multiple flood extents. Properties are specified by a point shapefile (or csv format text file) and the flood extents are defined as ASCII format depth grids.The tool also includes an option to apply user specified property level protection, e.g. individual property flood gates providing resistance to flood waters. This will modify the depth damage curves used to calculate property damages to reduce the impact of flooding up to a specified threshold, at which point the damage curve reverts to its original values.

This section describes how to apply property level protection to your depth damage calculations:

1. Open the Damage Calculator tool, load your flood depth grids and property datasets and specify your damage analysis as normal. This process is described in this guide in the section entitled 'How to calculate property damages from a flood depth grid'.

2. Define a property level protection dataset. This consists of two csv format text files that once created need to be placed in the same folder as your depth damage data to enable Damage Calculator to recognise them. One text file describes depth verses damage reduction factor relationships for one or multiple property level protection options. The other text file provides a name for each property level protection option you define and a cross reference ID to relate to the associated data in the data series file.

   An example pair of property level protection csv files are included within the example damage data included with in zip file packaged with Flood Modeller.

   You can use the example files as a start point and then either add new depth varying data series or edit the existing values. Note that Damage Calculator will use linear interpolation to calculate the required adjustment factor for depths lying between those specified in the table.

   The data files used in your analysis must have the names; PLPMeasures.csv and PLPFactor.csv. The format of each file is as follows:

PLPMeasures.csv

An example of this dataset is provided by Flood Modeller. This file defines one or multiple property level protection measures. The description of the measure is listed here and the associated adjustment factors (in the PLPfactors file) are referenced. If you have these data in your data folder you have the option of calculating the effect of property level protection on damages.

Required columns are:

• numPLPMeasure – numeric entry providing an index for each measure defined. This is used to cross reference to property level protection factors listed in the “PLPFactors.csv” file.

• strPLPMeasure – text entry providing a (descriptive) name for each specified property level protection measure listed. The entries in this field will be listed in the Property Level Protection tab of the Damage Calculator interface, enabling you to select a measure to include in your analysis.

• Comments – text entry for user to optional provide additional descriptions of each specified measure. Field is required in csv file but entries can be left blank.

PLPFactor.csv

An example of this dataset provided by Flood Modeller. This file defines adjustment factors to be applied to depth damage data for one or multiple property level protection measures. The same factors will be applied to all property types if you choose to analyse the effect on damages of a particular property protection measure (if you have these data in your data folder).

Required columns are:

• numPLPMeasure - numeric entry specifying the measure index each data entry is part of, as listed in “PLPMeasures.csv”.

• numDepth – numeric entry. Assumed to be in same units as the depth grids used in your Damage Calculator analyses, i.e. no conversions performed in tool (for MCM, depths specified in metres).

• numFactor – numeric entry. This is the factor to be applied at the associated depth to adjust the damage to account for the selected property protection measure. The impact of this factor can be seen in the Damage Calculator tool prior to starting a calculation. After switching on property level protection (by ticking check box on Calculation Information tab), two curves will be shown for each highlighted property type on the Depth / Damage Curves tab. One will be the original depth damage dataset and one will be the adjusted curve to account for the selected property level protection measure (selected in the Property Level Protection tab).

Note that these relationships do not incorporate any variations with property type. Thus, to include these in your analysis you may have to perform multiple runs of the damage calculator tool and merge and/or filter the outputs to get a definitive result, e.g. create multiple versions of your property dataset that each containing different groups of properties (e.g. filtered by type).

3. On the Settings tab of the Damage Calculator tool you will have already set the path to your depth damage data folder. Therefore, once you have specified your property level protection csv files and added them to this folder, the tool should be able to just pick them up and use them.

   Note: You may have to close Damage Calculator and then restart it for it to refresh and recognise your property level protection data. This is signified by the property level protection checkbox on the Calculation Information tab becoming enabled (so you can tick it).

4. On the Calculation Information tab, tick the box entitled “Calculate damages with property level protection”. A new tab will appear on the Damage Calculator interface entitled “Property Level Protection”. This contains details of all available sets of adjustment factors in both chart and tabular form. Select the dataset you wish to use in your analysis by highlighting it in the left-hand list.

   

   The Damage Calculator interface enables you to visualise the effect of the selected factors as the revised damage data will be plotted with the original damage data on the Depth/Damage Curves tab and also shown in the adjacent table, as shown below:

   

5. Your damage analysis should now be ready to start. Go to the Calculation Information tab and click the Run button.

   Results are produced in the same format as the standard damage analysis, i.e. in tabular form on a new “Results” tab that appears once analysis has completed. However, the table contains extra columns as damages are calculated both with and without property level protection applied. Furthermore, the output log will contain additional lines to say property level protection was applied in the analysis and references to which property level protection database was used and which curve set within that database was selected.