Use Flood Impact Analysis

The Flood Impact Analysis solution delivers a set of capabilities that help you prepare flood depth and elevation data, define flood impact areas, visualize the flood in 3D and share the information with the public or other organizations.

In this topic, you’ll learn how to use the solution by assuming the role of a user and performing the workflows below.

Getting to know Flood Impact Analysis

You will assume the role of a mapping technician responsible for analyzing the potential flood impact for your community. The Flood Impact Analysis ArcGIS Pro project includes a series of tasks to help guide your through these workflows. The first set of tasks will help you get to know Flood Impact Analysis

Get to know Flood Impact Analysis by completing the following steps:

  1. Start the ArcGIS Pro application and open the Flood Impact Analysis project.
  2. On the View tab, in the Windows group, click Catalog, and click Catalog Pane.
  3. In the Catalog pane, expand the Tasks folder, and double-click on the Getting to know Flood Impact Analysis task and go through each sub task.

Understanding the Flood Impact Analysis solution

Flood Impact Analysis supports a series of workflows that streamline the process of developing flooding scenarios to help plan for a flood event. These workflows include preparing the data for analysis, defining the flood impact area and the impact on infrastructure, facilities and buildings, sharing the flood impact information, visualizing the flood impact in 3D, and sharing the impact in 3D.

This task will introduce you to the capabilities, data requirements to analyze flood impact and visualization in 3D.

Download sample data

Sample data is provided to help you learn how to use the Flood Impact Analysis solution. A link is provided to download sample data for Baltimore. Using the sample data the first time will help you learn how to use the tasks and how to organize your data.

Start using Flood Impact Analysis

The Flood Impact Analysis project includes a task workflow which provides a structured sequence using tasks and steps. Follow the steps in this task to learn how to use the Flood Impact Analysis solution.

How to use Flood Impact Analysis

You will assume the role of a mapping technician responsible for creating the flood impact analysis and sharing the results with emergency management, public works and planning agencies. The Flood Impact Analysis ArcGIS Pro project includes a series of tasks to help guide your through the workflows below.

To conduct the flood impact analysis, complete the following steps:

  1. Start the ArcGIS Pro application and open the Flood Impact Analysis project.
  2. On the View tab, in the Windows group, click Catalog, and click Catalog Pane.
  3. In the Catalog pane, expand the Tasks folder, and double-click on the How to use Flood Impact Analysis task.
  4. In the Task Pane, click on the How to use Flood Impact Analysis task group to expand the collection of tasks.
  5. Follow the steps in each task.

Prepare flood depth and elevation data

Accurate analysis and visualization of the flood impact analysis will depend on several factors such as: Availability of flood depth data in the form of raster, ground elevation data such as Digital Terrain Model (DTM) or LiDAR, and features describing the assets to be analyzed such as roads, bridges and buildings. The data preparation workflow includes a series of tasks to help prepare the data for analysis. A description for each task in this group is listed below.

Prepare flood depth rasters

Flood depth data is necessary to determine flood impact to the community at each flood stage. Flood depth grids or raster files contain a flood depth value within each cell in the raster. Flood depth at a given point can help determine the impact to buildings, roads, or bridges.

The risk value for each raster is read from the riskTypeTable for the chosen risk type. You can find the riskTypeTable in the FloodImpactAnalysis.gdb. You can use the existing risk types, modify them or you can add another entry.

To remove negative values, extract flooded areas and create the flood depth geodatabase, follow the steps in the Prepare flood depth rasters task.

Prepare water surface elevation raster

Water surface elevation (WSE) includes a value within each raster grid cell. However, the value describes the elevation of the water surface within each grid cell and is a measurement from a fixed zero elevation such as provided in the NAVD88 vertical datum. Water surface elevation (WSE) data can be used to calculate bridge heights above flood stages and to visualize the flood stages as 3D surfaces.

To create water surface elevation raster, extract flooded areas and crate the water surface elevation input geodatabase, follow the steps in the Prepare water surface elevation raster task.

Define flood impact

Effective flood response planning begins with a better understanding of the potential flood impact. This task is designed to step through a standardized process to create and analyze the impact of each flood scenario on your community. A flood scenario can be defined in the risk type table as a percent chance of flooding, historical average such as 100 year, or number of feet above normal. A description for each task in this group is listed below.

Create flood impact areas

The flood impact area defines the geographic extent for each flood depth scenario. The flood depth data prepared in the Prepare flood depth and elevation data task group will be used to create the flood impact area. These flood impact areas will be the foundation for analyzing impact to buildings, roads, or bridges in each of the subsequent tasks.

To create flood impact areas and add them to the map, follow the steps in the Create flood impact areas task.

Analyze roads

This task allows you analyze impacted roads by calculating depth of flooding for each road segment for any number of flood levels. The flooded roads can be an impediment to successful evacuations for first responders and community members when it is unknown which roads will be impacted. You can also symbolize the impacted roads for each flood impact area. The result will be a new feature class representing road segments with a depth attribute for each flood scenario.

To analyze impacted roads and symbolize the impact, follows the steps in the Analyze roads task.

Analyze low water crossings

This task allows you to calculate depth of flooding for each low-level crossing for each flood scenario. The result can be used to identify watch points for observers to report flood depth during the flooding event. The parameters for this step are similar to the road flood depth except for the buffer distance. If this distance is specified to be greater than zero, the analysis will run against the buffered input features. This parameter helps find points within the buffer distance that have been misplaced. You can then symbolize the low-level crossings by flood depth.

To identify low water crossings and symbolize the impact, follow the steps in the Analyze low water crossings task.

Analyze bridges

Use this task to calculate the bridge height above flood water surface for each flood scenario. Some bridges may have one side that is lower than the other. The bridge geometry is needed to calculate the height above the water surface instead of a single point along the bridge. Therefore, the bridge needs to be a 3D polygon feature instead of a 2D feature. This task will extract bridge surfaces from a lidar point cloud as 3D polygons, so they can be used in the next task to determine the height above flood level.

Note:

This task requires lidar point data stored in a LAS dataset . The bridge surfaces must have a separate class code in the LAS dataset.

Note:

This task requires that you have a water surface elevation (WSE) geodatabase as described in the Prepare flood depth and elevation data task.

Tip:

The result of this task is a new point feature with the minimum height above water surface for each water level in the WSE geodatabase. You can label the point with the minimum height attribute value to show how much clearance there will be below the bridge or how deep the water will be over the bridge if the height above water has a negative value.

To analyze impacted bridges and symbolize the impact, follows the steps in the Analyze bridges task.

Analyze buildings

Understanding building exposure to flooding can help response personnel prioritize evacuations and stage equipment where it can be used effectively. It can also help mitigation planners understand buildings that are good candidates for purchase and removal. Use this task to calculate flood exposure on building polygons or 3D building multipatch feature layers. The tool will use your water depth geodatabase and the specified risk type to calculate the flood depth exposure to each building within the flood impact area. You can then symbolize the features according to the calculated flood exposure attribute such as the flood depth. Using a graduated color ramp will allow you to illustrate the severity of the building exposure.

To analyze impacted buildings and symbolize the impact, follows the steps in the Analyze buildings task.

Share flood impact information (optional)

Once the analysis is completed, share the results with community stakeholders who can use the information to begin flood response or mitigation planning. Use this task to choose which flood impact layers to share, such as the flood impact area, impacted roads, bridges, and buildings for each flood scenario. Share the results for each flood scenario.

Note:

These tasks require ArcGIS Online or ArcGIS Enterprise 10.5 or later.

To allow others to see the results of the analysis, follow the steps in the Share flood impact information task.

Visualize flood scenarios in 3D (optional)

The best way to communicate the impact of a flood scenario is to show how it will impact homes, streets, bridges and neighborhoods. Visualizing the flood scenario in a 3D scene is a compelling way to communicate the potential flood impact in your community.

Note:

These tasks require ArcGIS Online or ArcGIS Enterprise 10.5 or later.

Show flood impact map in 3D

This task allows you to convert the map containing the results of the flood impact analysis to a 3D scene using 3D symbology and scene elevation. A digital terrain model (DTM) raster can be added to the 3D scene to provide a realistic scene for illustrating the impact of the flood.

Create 3D flood levels from raster

This task allows you to create 3D flood levels from raster input data. The result is a 3D version of the 2D raster data. For example, you may want to show a flood impact area at five feet against a building to illustrate the depth of flood on the building.

Source 3D basemap data (optional)

Visualization of 3D flood levels is more powerful when shown together with other 3D layers such as 3D buildings, 3D trees and detailed elevation. Use your organization's 3D basemap to complement your flood impact map. If your organization does not have a 3D basemap then use 3D Basemaps to create your own 3D buildings, trees and elevation surface.

Create depth elevation raster

A depth elevation raster can improve the visualization of flood impact in 3D scenes particularly, in flood scenarios with very shallow flooding. Use the create depth elevation raster task to create the depth elevation raster. You can repeat this task for every water surface elevation (WSE) raster.

To convert the map to a 3D scene and add the depth elevation raster, follow the tasks in the Visualize flood scenarios in 3D task group.

Publish 3D flood impact scene (optional)

Once the task visualize 3D flood scenarios is completed then you can publish a 3D web scene for your flood impact scenarios. The 3D web scene can be shared with stakeholders who are responsible for flood response planning and flood mitigation planning.

Note:

These tasks require ArcGIS Online or ArcGIS Enterprise 10.5 or later.

Publish 3D flood impact scene

Use this task to set the coordinate system and publish the new 3D scene to ArcGIS Online or your organization.

Share depth elevation raster

Use this task to share the depth elevation raster that was created previously to help improve the visualization of the 3D scene.

To share the flood impact in 3D, follow the tasks in the Share 3D flood impact scene task group.

After you have shared the 3D scene and depth elevation raster, you can view the results of the Flood Impact Analysis in a Scene Viewer in ArcGIS Online or ArcGIS Enterprise. Share the scene with your colleagues to help them understand the impact of local flooding on your community.