Browse to Raster | Projections | Warp (Reproject) dialog.For example, the USA Albers Equal Area Conic USGS Version is routinely used by USACE within hydrologic modeling applications because this CRS preserves area, which is crucial for hydrologic modeling.ĭo NOT use an unprojected CRS, such as Geographic. Terrain data must by in a projected coordinate reference system (CRS) for hydrologic modeling. The watershed boundary is now added to the Layers tree.Select the File Source type ( 1), open the watershed boundary folder and browse to select the WBDHU10.shp file and click Add.Select Layer | Add Layer | Add Vector Layer.The merged raster is now added to the Layers treeĪdd watershed boundary data from previous steps (HUC-10 level shapefile is used in this example) to your project.Check Open output file after running algorithm option ( 6) and click Run.Select Save to file from the drop down menu in the Merged browse box ( 5), browse to the output file location and save the merged file with *.tif extension.
Under Advanced Parameters, assign the input "nodata" value to match the value specified in the input dataset's metadata (-999999 for the USGS terrain) ( 3) and specify the output "nodata" value (e.g. Navigate to Raster | Miscellaneous | Merge. This step is only necessary if you downloaded more than one terrain data set (two in this example). You can also add a basemap for reference by browsing to the XYZ Tiles and double-clicking on one of the available options. Browse to the terrain raster's location ( 2) and click Add ( 3). Select Layer | Add Layer | Add Raster Layer to add a raster layer with terrain data created in the previous step. Open QGIS and start a new project Project | New ( 1) or open an existing project Project | Open ( 2). In this example we merge, clip and project the DEM file in QGIS Version 3.16.3. The watershed used in this example is the 140 square mile East Branch Brandywine Creek watershed in Pennsylvania. We will use the watershed boundary to clip the extent of the terrain raster for smaller file sizes and faster processing. We will use it as an input to HEC-HMS to create a terrain dataset, which can then be loaded into a Basin Model for hydrologic analysis (see Creating and Linking Terrain Data into a Basin Model tutorial). A DEM is a representation of the bare ground topography (elevations) excluding trees, buildings, and any other surface objects. Refer to Downloading and Preparing Terrain Data for HEC-HMS Using ArcMap for directions. 
ARCMAP RASTER CALCULATOR NODATA SOFTWARE
In this tutorial we use free o pen-source GIS software QGIS to prepare terrain data in the form of Digital Elevation Model (DEM) raster from open-source elevation and watershed boundary data (see the tutorial on Downloading Elevation and Watershed Boundary Data).
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