Use a text editor to create a breakline file manually. You can then import this text file to use as breakline data for building the surface. For more information, see To Import Breaklines From a File.
The following is an example of a breakline file:
# Autodesk User-Defined Breakline File P1542.258750 179.318779 0.000000 Flow_Line 1190.721102 350.527660 0.000000 860.816542 446.044194 0.000000 588.600214 619.055276 0.000000 608.430540 743.406990 0.000000 565.164367 925.429066 0.000000 S1529.639450 179.318779 100.250000 EOP 1188.918348 357.736453 101.420000 1021.998725 330.653391 103.530000 594.008485 610.044279 102.870000 761.574952 744.929530 104.780000 610.233298 754.220180 103.410000 570.572642 923.626865 100.980000 P1542.258750 179.318779 0.000000 Flow_Line 1190.721102 350.527660 0.000000 860.816542 446.044194 0.000000 588.600214 619.055276 0.000000 608.430540 743.406990 0.000000 565.164367 925.429066 0.000000