EXTRAN Boundary conditions

You need to assign the appropriate boundary condtion to each outfall. As stated in the EXTRAN.DOC file:

* I1 line :
* JFREE : Number/name of outfall junctions without tide gate (no back- flow restrictiona
* NBCF : Type of boundary condition from the sequence of data group lines J1 - J4. E.g., if NBCF = 2, use the boundary condition indicated by the second group of J1 - J4 lines.

The example posted should read:
* JFREE NBCF
I1 '30K2018S' 1 ** System Outfall
I2 '29L3183S' 2 ** Bypass 7
I2 '30L2171S' 3 ** Bypass 6
I2 '30L2172S' 4 ** Bypass 5
I2 'NONAME06' 5 ** Bypass 4
I2 'NONAME07' 6 ** Bypass 3
I2 '30K1152S' 7 ** Bypass 2
I2 'NONAME03' 8 ** Bypass 1
* BOUNDARY CONDITION
*NBCF=1
J1 2
J2 431.18
*NBCF=2
J1 2
J2 539.74
*NBCF=3
J1 2
J2 518.56
etc...

Michael A. Gregory, P.E.
GregoryMA@CDM.com

Hello All

Is there a limit to the number of outfalls in the system defined as free, and with backwater w/ tide gates? My system has seven SSO's, and the traditional outfall. When I specify a CWSEL for each, SWMM uses the highest elevation for all outfalls. Listed below is last part of my input file.

In the output, All of the listed nodes have an elevation of 539.74 in the first printed time step

I1 '30K2018S' 2 ** System Outfall
I2 '29L3183S' 2 ** Bypass 7
I2 '30L2171S' 2 ** Bypass 6
I2 '30L2172S' 2 ** Bypass 5
I2 'NONAME06' 2 ** Bypass 4
I2 'NONAME07' 2 ** Bypass 3
I2 '30K1152S' 2 ** Bypass 2
I2 'NONAME03' 2 ** Bypass 1
* BOUNDRY CONDITION
J1 2
J2 431.18
J1 2
J2 539.74
J1 2
J2 518.56
J1 2
J2 515.86
J1 2
J2 498.79
J1 2
J2 490.86
J1 2
J2 481.05
J1 2
J2 476.05

Thanks
Todd Williams
Parsons Engineering Science