Introduction

This is a user guide for the Flood Modeller Damage Calculator tool. The tool is designed to estimate direct property damages (residential and commercial) caused by flooding. Furthermore, the tool is set-up to recognise that factors influencing the amount of flood damages change over time. This may be because of flows changing due to climate change or assets that manage flood risk failing. The tool uses epochs (scenarios) to recognise this. An epoch allows the user to define a different set of flood depths at a point in time. If multiple epochs are specified in the tool, it can perform annual averaged damage (AAD) and present value damage (PVD) calculations that combine damage analyses from multiple events in multiple epochs.

In addition, Damage Calculator can determine the effects of property level protection and perform risk to life calculations. Furthermore, in tandem with the property flood damages, it can also calculate additional property related damages, which are; vehicle damages, emergency services costs, evacuation costs, mental health costs and indirect non-residential property damages (AAD and PVD values are also calculated for these additional metrics).

The tool offers two format options for flood data inputs:

• Flood depth grids in ascii raster format (.asc) where each grid represents a different return period (AEP) within one or multiple epochs (scenarios).
• Flood depths as additional attributes in the specified property dataset (see below), which can be in shapefile (.shp) or text (comma separated, .csv) format.

Note: The tool allows you to re-use a dataset multiple times, i.e. to represent different AEP values in different scenarios.

Furthermore, your grid or attribute data can represent a water level instead of a depth. In this case you will also need to specify a (ground level) threshold field in your property dataset to enable the tool to calculate a flood depth for each property.

Your flood depth data must be combined with a specified property dataset (providing property locations and metadata, optionally including flood depth data) and depth-damage curves to calculate the damage for each property affected directly by flooding. These data are then summed to obtain total damage figures for each flood event with the option to also calculate AAD and PVD values and to perform risk to life calculations.

The tool has been developed in collaboration with the Flood Hazard Research Centre (FHRC), who are part of the University of Middlesex, UK (https://www.mdx.ac.uk/our-research/centres/flood-hazard). The approaches in the tool follow FHRC’s 2013 publication: Flood and Coastal Erosion Risk Management: A Manual for Economic Appraisal more usually referred as the Multi-Coloured Manual (MCM). To support MCM approaches, FHRC publish an annual Handbook for Economic Appraisal (usually referred to as Multi-Coloured Handbook (MCH) and updates of property depth damage data referred to in the MCM. With the appropriate licence these data can be downloaded from the website; https://www.mcm-online.co.uk/ in a format that can be used directly in Damage Calculator. If you have depth damage data from another source, it can still be used in this tool. However, you will first need to convert your data to the MCM format, which is a series of comma separated text files (.csv). This format is described in the user guide at How to setup my Damage Calculator depth damage curve data. The depth damage data is used in combination with property data which can be supplied to the tool in either point shapefile or csv text format. Note that in both formats each property is represented by a single point. Damage Calculator analyses each point to evaluate where it lies within your flood extent depth grid data (e.g. derived from 1D or 2D modelling) and thus what flood depth will be associated to each property for the calculation of damages (note that this is not necessary if your depth data is part of your property dataset).

The methods and underlying datasets used follow the approaches described in MCM. This allows the user to comply with the UK Environment Agency’s FCERM Appraisal Guidance that guides how the business case for flood risk management projects are developed in England.

The guide consists of the following sections:

• How to calculate property damages from a flood depth grid

• How to review Damage Calculator results

• How to calculate present value damages

• How to calculate annual average damages

• How to apply property level protection thresholds to damage calculations

• How to create a property damage shapefile

• How to setup Damage Calculator depth damage curve data

• How to create an empty grid to represent a lower limit of flooding

• Custom settings provided for a Damage Calculator analysis

• How to include other contributions to overall damage costs

• Risk to life calculations

• Data requirements

• References