Task 1: Convert NHD waterbodies to polyline (for distance to water input)
Task 2: Use the Euclidean Distance command to calculate distance to water sources
Use "Extract by Mask":
Step 4: Convert to an ASCII raster using the "Raster to ASCII" command.
Your euclidean distance should look something like the above.
BRAT > Documentation > Implementation: Beaver Restoration Assessment Tool (BRAT) > Ungulate Capacity Model >