Hazus | Import a Depth Grid for a Flood Scenario


[ upbeat music ] [ sound effects ]
boom, whoosh, drip, splash, sparkle [ upbeat music fades in ] Welcome to the “Import a Depth Grid for a
Flood Scenario” video tutorial. In this video, we will provide an overview
of depth grids and walk through how to import a depth grid into Hazus to create a flood
scenario. A depth grid is a raster GIS dataset that
depicts variable flood depths throughout the extent of a flood event, and it greatly increases
the accuracy of your analyses because of the specificity of the water depths. Depth Grids are generated from a multitude
of source data, such as DFIRM, SLOSH, and event high water mark data. They can be obtained from FEMA’s Map Service Center via the link in the video description, from a colleague, from an HPR of a previously-created scenario, generated from other products, or from other outside sources. The depth grids from the FEMA Map Service
Center are ready for direct import into your scenario and often include the 500-year, 100-year, 50-year, 25-year, and 10-year flood events for your study region. If a depth grid for your study region is not
available to download, you can generate your own outside of Hazus. More information on this process can be found
in the “How to Build a Depth Grid” tutorial video. [ upbeat music ] We have our scenario open to a pre-made study region of Salt Lake County and are ready to import a depth grid for a riverine flood analysis. A reliable method for setting up a flood scenario
using imported depth grid data is to simply work your way down the Hazard menu. First, define the type of flood analysis you
will run in your study region. Open the “Hazard” menu and select “Flood Hazard Type…” Here you are given four options for the type
of flood scenario you can build: 1. Riverine only, 2. Coastal only, 3. Riverine and Coastal, and 4. Coastal Surge, which is a combined wind and flood analysis. For this example, we will select “Riverine
only” and click “Ok”. If you wanted to create a coastal analysis
scenario and import a depth grid for it, select the “Coastal only” option and follow the process
outlined in this video, as the steps are the
same. [ upbeat music ] Next, you can import the hazard data for your
flood scenario. Return to the “Hazard” menu and click “User
Data” to launch the User Data dialog box. Select the “Depth Grid” tab. Hazus is currently able to import depth grids
in the following formats: GRID, IMAGINE or IMG file, Tagged Image File or TIF, HEC-RAS
FLT, and file Geodatabase formats. Hazus uses the WGS84 projection, but if your
depth grid is not in WGS84, Hazus automatically re-projects the file on import. To start the import process, click “Browse”
and navigate to the folder that contains the depth grid you want to import. For this example, we have downloaded depth
grids from FEMA’s MSC for Salt Lake County to import into our scenario. For your own analyses, remember the name and location of the folder where you have stored your depth grids. From the selection dialog, you can choose
your depth grid, and even select multiple depth grids for your study region to support
running different types of analyses. For example, we could include both the 100-year and 500-year return period depth grids for this scenario if we wanted to run analyses
for both of these events. However, we will simply import the 500-year
depth grid. Before importing the depth grid into the scenario, you must provide Hazus with the measurement parameters and the return-period this depth
grid represents. Click “Set Parameters”. This depth grid is measured in feet and represents a 500-year event, so we will select “Feet” from the Units dropdown, and enter “500” into
the “Return Period” text box. Click “OK” and you will return to the User
Data dialog box. Click “OK” and the depth grid will be integrated
into your study region. A map of your study region will appear when
complete. Do not be alarmed if you do not see the depth
grid, it will appear when you create the scenario. Now, we will create our riverine flood scenario
using the imported depth grid. To begin, open the “Hazard” menu, open the
“Scenario” submenu, and click “New”. Note that if have imported multiple depth
grids and want to run multiple scenarios, you will have to repeat the following steps
for each scenario, and each scenario name must be unique. A Create New Scenario dialog box will appear
asking you to name your study region and provide a description. We will call our scenario “DepthGrid500”. It is important to note that spaces or special
characters are not allowed. Click “OK” and you will be brought to the
Map View where your imported depth grid appears and the New Scenario dialog box will allow
you to select the depth grid to use in this scenario you are creating. Click the “Add to Selection” button, and then
click and drag on the map to draw a rectangle around a portion of the depth grid you would
like to include in your scenario. When selected, the outline of the depth grid
will turn light blue. Click “Save selection” and then “OK” to confirm
your selection. As you can see in our example, the depth grid
turns dark blue. Next we will open the “Delineate Floodplain
tool in order to define the hydraulic analysis inputs of the scenario in order to reference
your selected depth grid. To do this, return to the “Hazard” menu, open
the “Riverine” submenu, and click “Delineate Floodplain”. The Riverine Hydraulic Analysis dialog box
will open. First you will need to define the type of
analysis using the top drop down. You are given three options: Full Suite of
Return Periods, which will run the analysis across all return periods from 10- to 500-year
flood events; Single Return Period, which will reference a single depth grid; and Single
Discharge, which is not for depth-grid-based scenarios, but for stream-discharge-type analyses. We will select “Single Return Period” since
we only have one depth grid and click “OK”. A prompt will appear asking if you would like
to continue. Click “Yes” and Hazus will process the analysis. This may take several moments. When the analysis is complete, the completed
depth grid and boundary polygon will appear on the map. A message will appear to let you know that
the scenario was created successfully. The orange outline you see is the inundation
boundary. The varying shades of blue represent flood
depth, with darker shades signifying deeper
water. Congratulations! In this video, you learned about depth grids and how to import a depth grid into Hazus to create a flood scenario. Look for more Hazus video tutorials on the
FEMA YouTube channel. [ upbeat music fades out ]

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