# How to Quantify the Economic Damages of Flooding with a 2D Model

October 15, 2020

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## Using InfoWorks ICM’s Riskmaster

Global floods will affect 147 million people a year and cost \$700 Billion by 2030 – according to data from The World Resources Institute.

As costly flood damages can cause severe disruption to communities, as well as strain city resources for repair and mitigation, it is critical for infrastructure managers and city officials to have accurate information and models to help them prepare for flooding.

To do this, many cities maintain hydraulic and hydrologic models of their connected wet infrastructure to provide a basis for simulation and analysis of flood risks.

However, many engineers may be unaware that a 2D model can also quantify the economic risk of flooding – should it occur at a level that is damaging to surrounding buildings and critical facilities.

### Developing a Risk-Based 2D Modeling Method

Risk-based 2D modeling goes beyond simply calculating the depth of flooding to provide a cost-relationship between flooding, and the surrounding buildings that the flooding may impact. Provided below are the 3 steps that can be used to create a 2D model that considers economic costs resulting from flood damages.

### Creating a Damage Function

First, an economically focused flood model uses “damage functions.” These functions establish a relationship between the depth of flow and the total plan area of a building, type of building, and the amount of cost per square foot dependent on the type of facility that is at risk. A damage function will also store the duration of flooding so that all aspects of potential flood risk are considered when quantifying cost.

#### A damage function analyzes the relationship between flooding depth, flood duration and building characteristics to calculate the potential cost of damage.

Engineers can use damage functions to assess and manage the hydraulic infrastructure that protects assets from flood events.

### Distributing Economic Risk with Damage Receptors

Next, the key locations that are undergoing a damage assessment in the model are identified as “damage receptors”. These damage receptors are assigned to polygons (which represent buildings) in the model and each can be analyzed with their own damage function.

This allows each polygon / building to be attributed with its own cost quantification and generates a unique result for each building.

### Considering Event Probability and Annual Damage

Potential cost can then be added up for each damage receptor to provide a total damage value for each return period.

### Using Expected Annual Damages for Better Planning

Taking this approach to 2D modeling provides engineers and city infrastructure managers the chance to better understand flood damages based on:

1. The average of flood damages calculated over a number of events and scenarios

2. The total damages at individual buildings for each event multiplied by the event probability

3. The expected damage for all events and return periods

This flood-risk methodology analyzes a hydraulic system based on the evaluation of the consequences derived from the service of the hydraulic infrastructure rather than solely system performance. The result is the ability to consider the expected damage per return period event, allowing for an understanding of the critical return period and duration events for either network wide impacts or building specific aspects.

Ultimately, this type of economically focused 2D modeling provides a comprehensive view of the performance of the hydraulic system and the consequences derived from flood events. Now, engineers and cities can plan more effectively and with confident flood disaster resilience in mind.