Recommended GIS Skills

Introduction

This tutorial introduces you to some of the geospatial skills that will be useful for pre-processing inputs for HEC-FDA 2.0. For this tutorial, we'll use a commonly used geospatial information systems (GIS) software tool called ESRI ArcGIS Pro. The version of ArcGIS Pro used in this tutorial is 3.0. (Note:  USACE users can download ArcGIS Pro (Version 3.0) from the UACE App Portal (click here to download the software), as of 1/12/2013.) The instructions included in this tutorial assume readers have a basic understanding of ArcGIS Pro, including how to open a new project and import simple geospatial data into the map window.

The tutorial is organized as follows: First the user is shown how to generate an impact area utilizing an existing raster or by creating a custom polygon shapefile. Then it shows how to use the impact area to select structures for a structure inventory. Once the user has a structure inventory, reaches can be delineated. Finally, some further refinements to the structure inventory are discussed.

Impact Area

HEC-FDA 2.0 requires an impact area to delineate the boundaries of the study's area of interest, such as the one below. For more information regarding impact areas in HEC-FDA Version 2.0, review Impact Areas.

The impact area will take the form of a polygon shapefile that can be imported into HEC-FDA 2.0. This may sometimes be provided, but often this will need to be generated by the user. 

There are two primary ways to generate a polygon shapefile impact area in ArcGIS Pro:

1. Use a water surface elevation (WSE) or depth grid raster dataset of the largest/rarest annual exceedance probability (AEP) event modeled for the FDA study, typically the 0.2% or 500-year event, or 
2. Generate a custom polygon shapefile and draw the boundaries of the impact area.

The first approach is preferable since it minimizes human error. However, this tutorial provides instructions for using either approach for generating an impact area polygon shapefile for the example study area. (For more information regarding the example study area used in this tutorial, review Example Study Data).

Utilizing Raster

A hydraulic model of the existing conditions is required to run FDA 2.0, so a WSE or depth grid raster of the largest AEP event modeled should be available by request to the H&H engineer assigned to the project.

Step 1. Add the raster to the map window by selecting Add Data under the Map tab as shown in the image below, and click Data. Navigate to the folder where the raster is saved and select and import the appropriate file (e.g., Depth .002 AEP (ft)). The example data used is from Muncie, Indiana, and the 0.2% AEP event is shown.

Step 2. Under the Analysis tab, select Tools and type "raster domain" in the geoprocessing search bar. Select the Raster Domain tool as shown below.

Step 3. In the Raster Domain geoprocessing tool, select the raster from the Input Raster dropdown box. Select "Polygon" from the Output Feature Class Type dropdown box, as shown in the image below. Keep the default values for the remaining options and select Run.

This generates a polygon shapefile of the outline of the raster as shown below. While the raster contains unique values for flood depth in each cell, the polygon shapefile that was generated here only contains one value for the length of the outline and the area of the entire shape.

As you can see, there is a swiss-cheese effect that can occur due to the extent of the estimated flooding that the raster represents. In order to smooth this out and create one continuous shape for the impact area, you'll need to add a buffer to the edges of the polygon.

Step 4. Under the Analysis tab, select Tools and type "buffer" in the geoprocessing search bar. Select the Buffer tool as shown below.

Step 5. From the Input Features dropdown box, select the polygon shapefile created in Step 3. Click the folder next to the Output Feature Class box and select a location to save the impact area shapefile. Name the shapefile (e.g., "StudyArea") and add ".shp" to the end to denote a shapefile feature class. Choose the buffer distance that shape will extend beyond its current boundary, such as 250 feet. Keep the default values for the remaining options as shown in the figure below and select Run.

This generates a new polygon shapefile with smoother edges and a continuous shape as shown below. The impact area polygon shapefile is complete and may be used to determine the boundaries of the study area within which structures may be selected for the analysis. Later, we'll split this impact area into sub-sections, or reaches.

Custom Impact Area Polygon

Alternatively, if a WSE or depth grid raster is unavailable, a custom polygon shapefile may be drawn. The user will need to have an idea of where the boundaries of the area of interest are delineated. This is the less ideal method of generating an impact area polygon shapefile because there is a greater chance of human error.

Step 1. Under the View tab, select the Catalog Pane as shown below.

Step 2. Right-click the project folder and select New >> Shapefile as shown in the below image.

Step 3. Name the shapefile, for example "CustomStudyArea." Select your preferred coordinate system and click Run.

This will generate a blank shapefile in the Contents pane. 

Step 4. Under the Edit tab, select Create and click on the blank shapefile you just created as shown below.

Step 5. Click on the first Polygon icon as shown in the image below to activate the drawing mode.

Step 6. Draw the boundary of the study area. Click once to set a vertex, move your cursor to a new point and click again to set another vertex, creating a straight line between the vertices as shown in the top image below. Do this along the outer-most edges of the study area of interest until you've created a continuous shape as shown in the bottom image below, double-clicking at the final vertex to close the drawing mode.

This generates a new polygon shapefile with smoother edges and a continuous shape. The impact area polygon shapefile is complete and may be used to determine the boundaries of the study area within which structures may be selected for the analysis.

Structure Inventory

Now that you have an impact area polygon shapefile, you might want to identify the structures that lie within the boundaries of the study area. For this tutorial, data downloaded from the National Structure Inventory (NSI) database (NSI 2022) was used. (For more information regarding the NSI review: National Structure Inventory.)

Step 1. Import the NSI 2022 structures for the state that your study area is within as shown below. 

Step 2. Under the Map tab, select Select By Location. Select the NSI dataset in the Input Features dropdown. Select "Within" from the Relationship dropdown. Select the impact area shapefile you generated as the Selecting Features. Keep the default values for the remaining options as shown in the figure below and select Run.

This will result in the structures within the impact area being highlighted.

Step 3. Right-click the NSI 2022 dataset and hover over Selection. Select Make Layer From Selected Features as shown below.

This will generate a new layer with only the structures that were highlighted within the boundaries of the impact area.

Step 4. From the Contents pane, toggle the other layers off, leaving only the new layer toggled on as shown in the top image below. In the Contents pane, right-click the new layer and hover over Data. Select Export Features as shown in the bottom image below.

Step 5. Choose the new layer from the Input Features dropdown box. Click the folder to the right of the Output Location box and select the folder to which you want to save the structure inventory. Name your structure inventory with ".shp" at the end to denote a shapefile feature class in the Output Name box and select Run.

This will generate a new structure inventory including only those structures within the impact area as shown below.

Now that you have a structure inventory and an impact area, you may want to subdivide the impact area to create separate reaches within the study area. As shown below, structures of the same type (i.e., residential vs non-residential) may be clustered together and so it might make sense to group them together inside a common reach for reporting purposes. There are potential engineering, social, economic, political and other considerations for delineating your reaches, so be sure to discuss with H&H and the other available team members for further input on how to define reaches.

Separate Reaches

Once you've determined where your reaches should be delineated, you can proceed with splitting the impact area.

Step 1. Under the Edit tab, select the Split tool as shown below. Click Split in the Modify Features pane.

Step 2. Determine what shape you want your reaches to take. Click the edge of the impact area to initiate the splitting at that point. Move your cursor to a new point and click to create a new vertex. This creates a straight line between the two vertices where the polygon will be split. Continue placing new vertices to draw the shape of the reach you are delineating. When you're finished, double-click at the final point on your reach to complete the split.

Step 3. Repeat Step 2 for each portion of the impact area that you wish to subdivide. In the attribute table, you'll notice that there is a row for each subdivision of the impact area that you've created, as shown in the image below.

Step 4. Click Add in the attribute table to add a new field, as shown above. Add two new fields for the Reach ID and Description and set the appropriate type (e.g., Text) from the Data Type column, as shown in the image below. Click save at the top and close the Fields window.

Step 5. In the Attribute Table, the two new fields you created will be on the far right. Enter unique reach IDs/names and descriptions for the separate reaches by clicking in the table to edit. 

Additional Actions for Structure Inventory

Now that the study area has been subdivided into separate reaches/impact areas, you'll want to add the reach name and description to the structure inventory. You'll also want to add new x-y coordinates if you've moved any dots for accurate structure placement.

Add Reach ID and X-Y Coordinates

Step 1. Right-click the structure inventory and hover over Joins and Relates. Select Add Spatial Join. Select the structure inventory from the Target Features dropdown box. Select the impact area from the Join Features dropdown box. Under Fields, scroll the bottom of the list and remove all fields from the impact area except those two you created. Click OK.

You've added two new fields to the structure inventory that include the reach ID and description that each structure belongs.

Step 2. Under the Analysis tab, select Tools and type "add xy." Select the Add XY Coordinates tool as shown below.

Step 3. Select the structure inventory for the dropdown box and select Run.

Now you've added two more columns for latitude and longitude coordinates, in addition to the reach ID and description as shown below on the far right of the Attribute Table.

Step 4. Finally, save the final structure inventory to your preferred folder location by right-clicking the structure inventory layer and hovering over Data. Click Export Features and select the structure inventory from the Input Features dropdown. Select your desired folder and name the shapefile with ".shp" at the end to denote a shapefile feature class. Click OK to save.

Converting Flat File Types to Spatial File Types

For structure inventories that are in .xlsx, .csv, or .txt format that need to be in a shapefile format, those file types can be imported into ArcGIS Pro using longitude-latitude coordinates. If the file does not have longitude-latitude coordinates, you will be unable to convert the file type using this method.

Step 1. Identify the column headers for the coordinates. In the figure below, columns AI and AJ contain POINT_X and POINT_Y.

Step 2. In ArcGIS Pro, click Add Data and select XY Point Data. 

Step 3. Click the folder next to the Input Table box and locate the file you want to import. Select the corresponding X and Y column headers in the X Field and Y Field. Click Run as shown below.

The flat file structure inventory has now been imported to a spatial shapefile in ArcGIS Pro.