Here is an example and Figure 1 shows the format (from Iface.c in SWMM 5)
SWMM5 Interface File
This is from the 1st line of the SWMM 5 Model in the Title/Notes Section of the Data
900 - reporting time step in sec
1 - number of constituents as listed below:
FLOW CFS
1 - number of nodes as listed below:
10208
Node Year Mon Day Hr Min Sec FLOW
10208 2011 02 22 00 00 00 0.000000
10208 2011 02 22 00 15 00 0.000000
10208 2011 02 22 00 30 00 0.000000
10208 2011 02 22 00 45 00 0.000000
10208 2011 02 22 01 00 00 0.000000
Figure 1. Graph of the lines in the SWMM 5 Interface File