The DRC requires gradients between rivers, canals, and fields to be defined. These are provide through a set of "DistanceTo" tables. These gradients are derrived from elevation data. Below is a description of the process for creating the digital elevation model (DEM) used for computing DistanceTo gradients.

Note, it is possible to perform all the necessary functions outside of an ArcGIS environment, however, the process is more involved and requires running a compiled executable via the Command Prompt. 

Acquire UCRAF Toolbox

Locate the UCRAF Toolbox in the 'UCRAF_ControlTool' repository. 

C:\...\UCRAF_ControlTool\ArcGIS\ArcToolbox

Open a new project in ArcGIS Pro and add the UCRAF Toolbox.

Go to Insert —>Toolbox —>Add Toolbox

Select the UCRAF.atbx file and hit 'OK'.

Elevation Tiles

Elevation tiles are available for the entire nation from the U.S. Geological Survey National Map. 

https://apps.nationalmap.gov/downloader/

For detailed instructions on downloading tiles from the National Map see here.

Basin Boundary

A boundary file (polygon shapefile) is needed to define the overall extents. It may be best to start with shapefile containing USGS-defined Hydrologic Unit Codes (HUCs) and select the hydrologic unit(s) associated with the specific area of interest and then export these polygons to represent the basin boundary. This HUC subset defines the extent of the DRC model and trims the data to this particular region. This file is used several times for preparing DRC inputs. 

Hydrographic Unit data are available for download over the entire nation from the U.S. Geological Survey National Map. 

https://apps.nationalmap.gov/downloader/

To create the basin boundary file, select the HUC polygon either by name(s), HUC number(s), or by location(s). Then right click on the layer in the Content Pane —>Select Data in the popup menu —>Select Export Features and specify a name and location for the output file. This should be saved a shapefile as it will be used later when populating the geodatabase. 

This HUC boundary file may need to be modified to include components of the irrigation system that fall outside this HUC boundary. Hydrologic boundaries represent natural flow divides. There could be relevant fields, canals, and pipelines that extend beyond the natural divide. There could also be areas that are not relevant encompassed by the HUC boundary. In that case, it may be possible to reduce the area before running the 'Populate Geodatabase' tool.

Mosaic Digital Elevation Tiles

The UCRAF Toolbox should now appear in the 'Catalog Pane'. Expand the toolbox and double click on the 'Create DEM' tool.

The 'Create DEM' tool should open. This tool mosaics a set of DEM tiles into a single contiguous DEM.  The user specifies the location where the tiles are stored (intermediate files will be created in this location and then removed at the end of the process) and loads the individual tiles along with a shapefile depicting the overall boundary. 

The 'DEM' parameter is where the output filename and file path is set. Ensure that this is is a GeoTIFF by giving it a .tif extension. 

Hit 'Run'. This tool may take a considerable amount of time to complete. Keep the command window that pops up open until the tool runs to completion.

This creates monolithic rectangular Digital Elevation Model (DEM) trimmed to model extents.